/ Motoring

Petrol vs diesel – which fuel is cheapest in the long run?

It’s hard to ignore the incessant sky-rocketing prices at fuel stations – diesel has tipped over the £1.50 a litre mark on many forecourts. With petrol 7p cheaper a litre, is diesel now a no-go?

With no sign of a let up in fuel price– and the possibility of a 3p fuel tax increase in August to rub salt into the wound – is now the time to ditch your diesel and go for an efficient petrol-engine car instead?

Although the 7p difference between petrol and diesel may not sound like much, it equates to nearly £4 more every time you fill up. For example, a Ford Focus hatchback with 55-litre fuel tank will cost you around £80.19 to fill up with diesel, but £76.34 with petrol.

If you only fill your tank up twice a month, it looks like you’ll be losing out on over £90 a year with diesel.

The cost of filling up my car

Even the cost of filling up a small car has gone up by more than a third over the past few years. As the price indicator on the fuel pump ticked swiftly past £60 when I was filling up my Renault Modus last night, I winced and was sorely tempted to stop – how could a supermini cost that much to fill up?

Yet, I’m still better off than plenty of other motorists right now. Why? Because my Modus has a petrol engine. If it had a diesel, it’d have cost at least £3 more.

So should I be smug about my fuel choice, or does the old adage about diesel cars being cheaper in the long run still hold true?

Having plugged the relevant info on my car’s purchase price, mpg, annual mileage and fuel price per litre into our clever petrol vs diesel calculator, I don’t really have that much to be happy about.

Does diesel pay in the long run?

Even with the current painfully high diesel prices, in just under two and a half years I’d be able to recoup the extra cost of filling up a diesel car over a petrol one. I’d even be able to recoup the extra cost of buying a diesel model.

Why? Because despite all the extra costs that come with diesel models, they always do more miles per gallon than petrol ones. For example, the 1.6 petrol Ford Focus averages 47.1mpg, compared to the 1.6 diesel stretching to 67.3mpg.

I drive over 12,000 miles a year, so spend an awful lot on fuel, That means going for a diesel model may well actually save me money in the long run, despite current prices. I’m certainly tempted.

If you’re thinking of buying a new car, how much are the current eye-watering fuel prices affecting your choice of diesel or petrol car?


I am planning to change my car in the next year and will have to decide on whether to stick with diesel or switch to petrol. My first diesel car was bought in 2002 when the main dealer was offering new Golf diesels at the same price as petrol models and the offer was too good to miss. My present diesel Golf was another new car that the dealer offered a good discount on, presumably to make way for new stock.

I would prefer to stick to diesel, but I drive only 7000 miles a year. What I buy will depend on what is on offer. I am not in any hurry to change my car and I will keep an eye on what is available from local dealers, whether that is petrol or diesel.


You’ve missed one essential consideration…depreciation. If you add up cost of ownership over a period, you’ll find that depreciation on anything but the oldest cars makes all other factors, including fuel costs, pretty insignificant for most drivers. (Insurance could be an even bigger hit for the young).

Most diesel cars depreciate more slowly than their petrol equivalents, reflecting their tendency to be longer-lived and (b) fuel cost is an even greater consideration for anyone buying an older car.

There are other things to take into account too, such as cost of servicing.

When replacing my car, I put together a simple spreadsheet to calculate cost of ownership of all the cars I’m considering. It includes factors such as cost of money (interest on a loan and/or loss of interest on capital), depreciation, road fund licence, insurance, servicing and fuel. The results are often surprising.

Keith Merry says:
16 March 2012

Can anyone please tell me why diesel in the UK is more expensive than petrol… Other countries that I have visited it has always been that diesel is cheaper than petrol..Are we being ripped off again?

Colin Samson says:
19 March 2012

The excuse for higher UK diesel prices is to do with lack of UK diesel refinery capacity. The UK cannot refine enough diesel for domestic supply, so has to import some refined diesel; this is more expensive. It seems that we are the victims of the recent success in UK sales of diesel cars; more refineries are needed but the fuel companies don’t want to spend the money required to build more . . . just yet.

D M L says:
17 June 2013

I am sorry to say I am old enough to remember when diesel was a lot cheaper than petrol in the uk but as more diesel cars became available, guess what, up went the price of diesel and it has never been below petrol again , can anyone confirm that diesel is actually cheeper to produce than petrol? or is Keith Merry correct it is yet another case of keep quiet and we will rip you off.

Robrt J Tucker says:
16 March 2012

No matter what we the motorists plan..albeit petrol or diesel ;.the Government will swap about to keep that which makes most revenue for the Government. if people stop buying Diesel.the Government will bump up the petrol prices..if we continue to use diesel the price will increase..to maintain revenue…
the answer is get 20 petrol or diesel Customers and buy up a block stock of either….or maybe get 50 motorists to block reserve a stock at bulk prices from the Oil Companies….I’m sure that will beat the Tax man..


For many years diesel was significantly cheaper than petrol, then overnight Diesel suddenly became much more expensive.

I think we need to look at why this sudden change came about and why non commercial Diesel is so expensive. I think at the time the Govt said that drivers of Diesel cars were gaining by having a higher MPG and to have cheap fuel as well was too much of a good thing.

I have just purchased a small diesel car for my wife with the sole intention of running it on cooking oil, which is considerably cheaper.

Top Driver says:
16 March 2012

You are falling into the trap that manufacturers want us to by quoting official fuel consumptions. The majority of motoring magazines do the same which makes their cost comparisons meaningless. In the real world official figures are pure fantasy. To use your example, I run a 1.6 diesel focus which has done 12,000 miles so is well run in yet even with gentle driving and 65mph cruising on motorways I only get 52mpg – nowhere near Ford’s claimed 67mpg. I prefer the superior pulling power of diesels but am seriously thinking of switching back to petrol but, for the reasons given above, i find it impossible to make any kind of true cost comparison.

David says:
16 March 2012

“If you only fill your tank up twice a month, you’ll be losing out on over £90 a year with diesel”.

Nonsense. You won’t need to fill it up as often. 12,000 miles at 47.1mpg with petrol at £1.43 a litre will cost you £1656. Switch to diesel at £1.50 a litre, but with 63.7mpg and you’ll only spend £1284. A saving of £372.


Hello David, you’re right as Claire goes on to explain – diesel is better in the long run. We’ve made a quick edit just to avoid confusion for those who don’t get to the end of the Convo. Thanks.


Let’s ignore pricing, taxation and engine/car efficiency for a minute and think about these fuels purely as a source of energy.

Both petrol and diesel have similar calorific values – about 46 MJ/kg depending on the blend. BUT, petrol weighs 5%-15% less that diesel. Because both fuels are sold by volume, not weight, you actually end up with 5%-15% less energy for your money when you buy petrol.

This is one of the reasons why diesel cars use “less” fuel, when measured in MPG. If we measured fuel by weight, the diesel car would not outperform the petrol version by such a large margin.

As long as fuel is sold by volume, you should expect diesel to cost up to 10% more than petrol and be happy to pay the price, as you are still getting more energy per £.

Whether manufacturers need to change more for building and servicing diesel models is a separate debate. Given the enormous economies of scale in motor manufacturing, I suspect functional pricing is at work.


Meant to write: ” … need to charge more … “.


Anyone considering changing their car with fuel consumption in mind should take a look at the Real Life Fuel Economy Register on the Honest John web site ate http://www.honestjohn.co.uk/realmpg/
This takes input from many drivers on their real world fuel consumption and gives a much better guide than manufacturers’ figures. The more of us who use it, the better its data become.


I agree Alan, real life fuel economy is the best indicator, that’s why we do our own in-depth fuel consumption tests at Which? Car for all the most popular engines in each model range.
As well as the standard EU mpg tests, our testing also includes urban and extra-urban cycles under cold-start conditions (replicating getting into your car and driving away immediately as you might first thing in the morning) and a second test with the engine warmed up and the air conditioning on. We also conduct a motorway driving cycle at a top speed of 81mph with full throttle acceleration periods (replicating speeding up when merging onto motorways). Find out more at http://www.which.co.uk/cars/choosing-a-car/how-we-test-cars
The results can be found on the Running Costs page of every online car review and are the best figures to input into the Which? Car petrol vs diesel calculator.


Long distance trabnsport – trucks – historically used Diesel (and still do) because diesel is more efficient for such usage. It also makes sense for cars where many journeys are long.

For the driver who does predominantly short journeys, diesels will not get their particle filters sufficiently hot unless they go through a cleaning cycle which wastes loads of fuel. They are better off with an efficient petrol hybrid car.


This is getting tedious…we should fret about depreciation and reliability long before fuel consumption (although depreciation is less important for older, low-value cars).

Variations in fuel costs are generally insignificant against depreciation and the cost – not to mention inconvenience – of breakdowns and repairs.


If you keep a car for ten years or more, depreciation is not a very important factor in running cost. Unless you are unlucky, breakdowns and repairs should not be a significant cost if cars are properly serviced – provided that you avoid makes/models that are known to be unreliable.


I think you’ll find that, if you keep a car 10 years, you’re in a very small minority. Even if you do, and it’s, say, a £20,000 car, it may be worth nothing after 10 years or it may be worth something like £3000, depending on what you buy. Choose the right one and save £300 p.a. which could easily compensate for higher fuel costs.

That isn’t to say fuel consumption is to be ignored, just that it isn’t the first priority. If you can find a car that depreciates slowly AND has top fuel economy, that’s perfect.

Regarding breakdowns and repairs, of course they SHOULDN’T be a significant cost, but the fact is that, with many cars, they ARE. And people do keep buying unreliable cars, despite the best efforts of Which? My present car, owned from new, is 6 years old and has needed nothing but routine servicing. My friend’s Saab cost him best part of £3,000 in repairs over 6 years – £500 p.a. pays for a lot of fuel. As for my neighbour’s Alfa and my daughter-in-law’s Fiat, the less said the better.


I may be in a very small minority but my strategy of buying new and keeping cars for a long time has worked well for me. Buying new means that I am not inheriting someone else’s problems.

If you have kept your car for six years and only paid for servicing you have probably saved a fair amount of money compared with those who have changed their car once or twice in that time.

New cars are more economical but I am reasonably happy that my 10 year old diesel gives around 48 mpg over the year, despite being used for a lot of short journeys. All I have paid for is to have a door lock changed and the front electric windows fixed, and I have done all my own servicing except for changing the timing belt.


I’m with Wavechange on this. My strategy is to buy new and we hold onto our cars for around 10 years. It’s only significant advances in vehicle safety that make for a compelling change – like airbags and ABS.

Whilst it is possible to estimate the total cost of ownership based on the various factors Dave mentions above, the one unknown is the cost of fuel, so why would fuel economy be any less of a consideration than depreciation? And, ignoring hybrids and other advanced fuel-saving technologies, is there any car with high fuel consumption that depreciates more slowly than the equivalent model with a more frugal engine?

I decided to make the switch from petrol to Diesel when fuel was 80p per litre. I’m now spending an extra £1000 every year I hadn’t reckoned on, but my car’s depreciation hasn’t changed at all – other than on paper – because I have no plans to sell, until it becomes uneconomical to run or repair.

I know my car will be worth next to nothing at the end of 10 years, but I still choose one that is supposedly reliable, with low depreciation – just in case I do need to sell it within a few years of purchase – but with good fuel economy too, as I suspect £2-£3 per litre isn’t too far off.

PaulJ says:
16 March 2012

Not all diesels are suited to short journeys. Vehicles fitted with DPF filters need to burn off the excess soot and they do this on runs where the revs are higher for at least 15 minutes, so that a high temperature is reached to remove the excess soot.
People who only do short journeys, or mainly town work should not buy a diesel if it has a DPF fitted.


Agreed – and if it doesn’t have a DPF fitted you shouldn’t buy it because the emissions on a cold start are cumulatively toxic and far more harmful than without (which is still far more harmful than petrol emissions. Measuring only CO2 is fallacious when it comes to determining the mastiness of emissions).


Also agree, but not neccesarily high revs needed. A higher exhaust system temperature through travelling further also achieves the temperature required.


Roerjp, with regard to your above comment do you mean ” Agreed-and if it DOES have a DPF fitted you shouldn’t buy it…?” Unless I am out of date my understanding is that the introduction of DPFs for all diesel cars has resulted from EU legislation which was NOT based on solid medical evidence ie the necessity for DPFs is unproven. Has this state of affairs resulted from vested interests of the motor industry? From what I read DPF’s do cause a lot of bother. Also,
Honest John in the Telegraph points out the extra potential costs of running EU5 diesel cars when they are 3 to 6 years old which include replacement DPF’s, replacement Duel Mass Flywheels, replacement Exhaust Gas Recirculation valves, replacement Turbo’s and replacement timing belts and tensioners.The independent garage which services my 11 year old Mark 4 petrol Golf ( owned since new) is no longer recommending diesel cars so I will probably replace with a new petrol car . Meanwhile it is great to have a car with minimal depreciation!


Dave – I am an asthmatic who is strongly affected by diesel fumes, and I know others who have the same problem. Fortunately, modern diesel vehicles are generally much cleaner than those that used to be on the road and I welcome any measures that will achieve further improvements.


Hi Dave.

I actually did mean what I said – for reasons Wavechange identified. The emissions from unfiltered Diesel engines, particularly when cold, are claggy – full of soot and nanoparticles. the nanoparticles may not in themselves be allergens, but they potentiate allergy from other things. I am a strong believer that the rapid expansion of diesel engines in private cars without filters has accelerated the upward trend in asthmatics over the last decade or two. The curves of the growth of diesels and growth of asthmatics correlate quite well over the nineties, but asthma flattened somewhat in the back end of the noughties – as PSV filters came of age.


I’m pleased to report that my BMW 520D, complete with DPF, 6 years old this month, has so far suffered none of these problems. In fact, it’s suffered no problems at all apart from a few irritating trim rattles and buzzes. I suppose I should be touching wood…



Another factor that has helped some asthmatics is considerable reduction in sulphur content of diesel. Even red diesel, which is used in boats and in many agricultural/industrial engines will have to be virtually sulphur-free from the start of this year. Sulphur dioxide in exhausts does not affect all asthmatics but it is a bigger problem than particulates for some of us.


The difference between diesel and petrol prices has widened recently because of the large increase in demand for diesel ; diesel cars now make up over 50% of all cars in the UK I believe
Refineries were not designed to produce such a large proportion of diesel so market forces have increased its relative cost.

Diesel engined cars still tend to produce less CO2 per kilometer than petrol versions though.

Essexman says:
18 March 2012

A couple of points not touched on so far here. As someone who suffered from asthma for many years of my life I can see the anti diesel case. But unleaded petrol contains benzene & toluene, two very powerful carcinogens, which are mostly burnt off by the catalytic converter – but only when it’s warmed up. And with diesel at least you are not carrying a tankful of explosive in your tank. The flashpoint of even premium diesel is approximately 50c, for petrol it’s around -40c. It doesn’t get that hot, or cold in the U.K.


You are right about the flashpoint of diesel and petrol, and there has been a move towards diesel for boats, encouraged by the number of fires. Unfortunately, the autoignition temperature of diesel is substantially less than for petrol. What worries me most of all is the use of LPG as fuel.

Both diesel and petrol are potentially harmful and we should all drive and use public transport as little as possible.

Leaf user says:
19 March 2012

Electric cars, while currently expensive to buy, are very cheap to run and at the tailpipe (there isn’t one) do not generate any the pollutants mentioned above. Now that we’ve owned a Nissan Leaf for 6 months, neither of us would go back to an internal combustion engine (ICE) car for everday use. As electric vehicle (EV) batteries improve and more fast chargers become available, the usual excuses for not buying an EV will become irrelevant.


Batteries have barely improved over the years that we have asked them to do more, what makes you think that battery technology will improve at a faster rate in the coming years?

So the usual drawbacks of an electric car still remain, and will remain for many years to come.

I personally don’t drive that much in the week so I have a petrol engine (mini cooper s). It is however a small engine, but fitted with a turbo so you can have economy or performance, whichever you prefer at the time.

I might actually be one of the only people in the world who doesn’t think petrol that expensive.

Having recently had an operation and had to travel around on buses and taxis, I have to say any car, petrol or diesel, is worth every penny that we pay. Add to that the fact that Mini gave me 3 free MOT’s and I bought their TLC servicing pack (3 years servicing for £270), plus free breakdown and recovery and that minis depreciate slowly, I definitely bought the right option, small car, petrol engine + turbo.



I am encouraged by the developments with laptop batteries in the last few years. At one time you had to be very careful about how to treat these batteries to get decent life and now it does not seem to matter. Well that is my experience with recent Mac laptops. It’s not all down to the batteries and the electronics that control charging and prevent over-discharging are also important.

I agree with your thoughts on fuel prices, even if no-one else does. One of the reasons that most of us avoid small cars is that we sometimes need a larger car. If it was as cheap and easy to hire a larger car as it was for me to do at work, I would certainly run a small car rather than a medium car.


Agree with wavechange about the importance of battery management. The batteries in my two current laptops have been brilliant, but I think that’s mainly down to my choosing the option of limiting battery charge to 80% of capacity. Trouble is, while that’s great for long-term battery life, it limits the running time. I can live with that, in my laptops, but the range of the Leaf is too restrictive for me, as it is, without restricting the charge to less than 100%.

Also agree about car size…I run a big estate car, mainly so that we can fit everything in two or three times a year for self-catering activity holidays. Most of the time, I curse the size of it, but I can’t justify running two cars.


I have been informed another problem with some diesel engines is that their inlet manifolds can “gum up “with a curious wax like material which can occur as early as 30,000 miles.(This sounds to me a bit like the manufacture of polythene from the polymerisation of the gas ethylene!) The symptoms include loss of power because of increasing restriction to gas flow.The cure is an expensive clean up of the cylinder head.Diesel Ford Focus and diesel Golfs are named vehicles.


Sorry,the above post should have read “that their cylinder heads can gum up….”

Peter says:
19 March 2012

Just a simple question: Why is the UK pricing of diesel at the pump (when compared with petrol) so out of kilter with fuel prices in Europe? In all European countries, the Petrol/Diesel pricing is opposite to UK with price difference for diesel/litre being 5p or so cheaper than petrol/litre .

Essexman says:
20 March 2012

I think the reason diesel’s cheaper in much of Europe is that the fuel duty on it has been less there than it is on petrol, whereas in the U.K. it’s the same for both. So even when the base price of diesel is higher than petrol (most of the time these days!), it’s still cheaper in say, France & Spain. I’m not sure the non polluting electric car argument is sound, the electricity has to be generated somehow & it’s not all hydro/wind/solar. But it’s a start & better breathing exhaust fumes in the high street. They (electrics) still have one very big problem though, limited range – and they get even worse in cold weather.

Brian says:
20 March 2012

Diesels used to be reliable to very high mileages, but the modern diesel with turbochargers, particulate filters, dual mass flywheels etc – all neccessary to comply with emmission regulations – give expensive problems that can wipe out any potential fuel saving.


How does the cost of servicing compare for petrol and diesel engined cars?

I took my VW Golf 4 into the main dealer a couple of times when it was new (they did a poor job in my opinion) and apart from having the timing belt replaced I’ve done the servicing myself.

I know what’s involved in servicing my 10 year old car but plan to hand the job over to a garage and would like to know about servicing costs for modern cars, which may be a factor in deciding to buy a new petrol or diesel car.


Servicing costs are very variable. Phone a few dealers. Many offer packages up-front for very reasonable prices, e.g. £350 for 5 years on a BMW 3-Series or £400 on a 5-Series.

These typically only cover the basics, like oil, brake fluid, spark plugs and filters. You’ll still have to pay for brake discs and pads, etc. The packages are transferable, I think, so if you sell before the 5 years are up you have a powerful selling tool.

Several manufacturers offer free servicing for a number of years. Phone or visit a few dealers or check manufacturer websites.

Keep in mind that service intervals are longer than they used to be. Many modern cars have variable intervals and advise you via their displays, based on the sort of driving you do, when the next service is due. In the case of BMW, you can go anything up to 18,000 miles between services, if your journeys are mainly long ones on the open road.


18,000 miles between services?? That’s plenty of time for damage due to stone chips, split CV joint boots, etc to go unnoticed. I wonder how many cars are unfit to be on the road.

Of course users know that they are responsible for ensuring that their car is roadworthy at all times.

Thanks for the advice on checking what dealers include with the cost of a car.


Are you telling me you’re not smart enough to spot stone chips for yourself? In any case, do you really believe that garages check for stone chips, or even boot splits, as part of an oil change service (which is all many services are)? As for all those unfit cars, what do you imagine the MoT test is for?

Do you realise that many people do 18,000 miles in 6 months? Their cars will be serviced twice p.a. Those who take much longer than a year to do 18,000 will be told by their OBC that a time-based (rather than mileage-based) service is required. And, between services, cars over 3 years old need annual MoT certificates; a split boot means a fail. Just how often do you reckon should safety checks be carried out?

I’ve had my 5-Series diesel for 6 years from new and it’s had nothing other but four routine services. There have been no split boots…no faults at all, in fact. The extended warranty I paid for was a waste of money. It sailed through its MoT yesterday. I suspect the battery is on its way out, but that’s about it…apart from some stone chips, not that my garage has ever pointed them out.

You say your car is 10 years old. It sounds as though your thinking may be out of date. I took the trouble to reply with what I imagined was good news but you don’t want to hear it. How sad.


Sorry Aitch, I meant stone damage rather than stone chips to paintwork or glass.

I may be out of date and only an amateur mechanic but my life depends on my car being in a safe state. The mechanic who has occasionally done repairs on my car deplores the infrequent servicing recommended by manufacturers and I trust what he and others who hold the same view have to say. Look a the percentage of cars that fail the MOT.

I do not know how often safety checks should be carried out and perhaps we should be guided by those who carry out MOT inspections.

Anyway we have a different outlook, so let’s end the discussion.

Essexman says:
20 March 2012

The cost of servicing isn’t much more with diesels than petrol’s in my experience, though the more cramped engine bay of the diesel should mean higher labour costs in theory. The fuel filter, a serious piece of kit in a diesel will need to be changed more often though.

But Brian has it right, a lot more to go (very expensively) wrong in the modern diesel. Not that it necessarily will. Failed turbocharger (now fitted to all diesels) seem to crop up a lot, often caused by missed or late oil & filter changes. Insist on a synthetic oil come service time & get it changed once a year, or better still, every 6 months. And if you do it yourself (check Halfords online for right grade)you can be sure you get the oil you’ve paid for in your sump.


Thanks Essexman.

I appreciate the importance of frequent oil changes and already do what you recommend. On my present car it is possible to remove virtually all the oil (I have checked!) through the dipstick hole, making the job very easy, compared with removing the shield below the engine and draining the oil. I have had no problem with the turbocharger or anything else related to the engine so far. I have changed oil and done some other jobs more frequently than recommended with every car and motorcycle I have owned.

The point you make about the larger physical size of diesel engines can sometimes be very important, so perhaps the best way forward is to ask about servicing costs of models I am considering.

Incidentally, one of the ways that a VW main dealer let me down was by not attending to the fuel filter and then claiming that it was not a service item. I got an apology, a free brake fluid change and a fancy loan car in recompense.


When electric cars can do 200 miles on a single charge at night in winter I will consider buying one but not before.The motor industry might like to consider producing electric VANS as lots of tradesmen spend a lot of time travelling locally.

Essexman says:
20 March 2012

How do people who have to park in the street cope with charging electric cars? Not really practical to have a flex going across a pavement overnight to your car all night from your house..and that’s if you can find a space outside your house.

Wavechange, it’s my belief that manufacturers reccommended oil & filter changes are set by marketing men not engineers. The Haynes manual for my Fiesta TDCI reccommends every 6 months or 6,000m. Ford say every year or 12,500m..You can get 5L of 5W/30 synthetic oil for around £20 if you look around.

A basic service for a diesel car shouldn’t cost much more than on the petrol version..it’s I’d leave the fuel filter on my diesel to a garage every time. And a full tank of derv in cold weather helps prevent condensation in the tank & subsequent water contamination.


You are right about oil changes, Essexman. A senior member of VW staff told me that the long period is for the convenience of customers and if I wanted my engine to last, the oil should be changed more frequently than recommended.

Unless residential streets have electricity points installed – like marinas have for boats – electric cars are likely be practical only for those who have their own garage.

I have never seen any visible water in my diesel cars (about 20 years) but water in fuel could become more of a problem as the biodiesel content is increased. ‘Diesel bug’ (growth of bacteria and/or fungi at the fuel/water interface) is fairly common in boats, which are often unused in the winter months and biodiesel seems to be making the problem worse. Diesel bug blocks filters, but can cause much more serious problems. Hopefully the filling stations will implement measures to keep their fuel dry, so it is unnecessary to keep our tanks as full as possible – but that’s is standard practice for conscientious boat owners.

I’m beginning to think that buying a petrol car might avoid a few problems. Now that contact breakers and carburretors are history there is no need to buy a diesel car for reliability.

Essexman says:
20 March 2012

From what I’ve read, if you are planning on doing mainly short journeys around town, a new diesel car may not be a good choice due to the diesel particulate filter fitted to them now. If they don’t get hot enough to burn off the soot (passive regeneration) the car goes into ‘active regeneration’ mode which can lead to engine oil being diluted by fuel..

I could well be being paranoid over water in diesel if you’ve not had any problems all that time Wavechange. No reason a diesel should be more or less reliable than a petrol I’d have thought, apart from no H.T. leads to get damp. The cold starting probs of older diesels seem to have gone what with high pressure common rail injection & better fuel additives. Mine started first time from cold @ an indicated -7.8c back in Feb, though it turned over noticeably slower!

Many car problems these days seem to be caused by electronic glitches, probably the best advice is to check the Which brand reliability pages.

Full marks to the VW man for giving you the honest, rather than corporate information about oil changes.

Just another thought on electric cars. They’re going to be cheap to run (if not to buy) as domestic electricity is subject to 5% VAT, whereas around 65% of the cost of petrol & road diesel is tax. If electric cars became more affordable & practical, would any government allow that imbalance to continue?


The comments about diesel particulate filters are very useful. Hopefully dealers will alert prospective purchasers and the issue will become common knowledge, or an effective solution will be found.

My current 10 year old car is an early version of the common rail injection models and has always started at the first attempt even in cold weather, despite having been used frequently for short journeys. I replaced the battery after six years, before it let me down, and put in a bigger one.

For years many of my journeys have been less than two miles, back and forward to work. Now that I am retired my journeys are longer and less frequent. I am not worried about particulate filters, but increased biodiesel content of diesel could be the next big worry in the world of diesel vehicles. I hope not.

Ken Grahame says:
7 April 2012

I’ve just bought a new diesel car. It’s returning 67.3 mpg up and down the pennine hills in which I live. My previous petrol car, with only an extra 200cc under the bonnet wouldn’t do 30mpg here.

Maybe someone has explained this already elsewhere, but just to correct my ignorance, could someone explain why we pay more for Diesel than petrol, when the rest of the EU are the other way round? (With an impending 3000+ mile trip to Southern Spain, that’s another good reason for choosing Diesel!!!).

Dan says:
12 May 2012

i was looking for a old hatchback between 1000 – 2000 pounds and was so set on getting a diesel, but after alot of thinking ive put it down to a 1.6 petrol or 1.8GTI …. both rather bad on fuel economy i know, but the cars are almost 800 pound cheaper than there diesel counterparts and the insurance was cheaper so in long run it is some times cheaper to go for a petrol car which drinks more fuel.

Keith Hudson says:
1 June 2012

Well, we have just made the decision to replace our 2nd car, a BMW120d auto with a newer 120i petrol version. Why? because the 2006 diesel car is always used on short journeys of 10 – 15 miles, work, shopping school runs etc. All long trips are in our new 520d touring ( at best 42mpg by the way) . The 120d with full BMW history averages 31 mpg. That’s about all we can expect. A newer efficient dynamics version (we borrowed one) achieves 40 mpg. The 120i on the other hand is a 44 mpg petrol car, suited to short journeys, and on loaning a demo I achieved a staggering 42 mpg driving really hard.
Fuel efficiency of petrol cars especially the new BMW’s has improved so much that when you take the differential in price between petrol and diesel into account, and the poor economy of many diesels on short trips (especially in winter) it’s a no brainer – petrol wins. We also paid £2k less for the same spec car than if we had gone for an equivalent diesel version. So, lower cost, lower pollution, lower noise pollution and a quieter drive. We are very happy to now be able to drive away from the pumps not smelling of diesel, and 50p per gallon better off!


When you consider price, maintenance and insurance, I’m not sure that these BMWs are really the most cost effective solution, but if it has to be a BMW rather than a Ford or other cheaper car to take to the supermarket and school, I suppose it makes sense.


What really matters is not price, maintenance, insurance, or even mpg or tyre costs, but total cost of ownership. When you take into account ALL factors, notably depreciation but also things like up-front servicing packages, cars with higher prices often cost least, in the long run. Yes, I know, wavechange, that you keep your cars forever (almost) but most of us enjoy changing them every few years – motoring is about pleasure and fun as well as practicality and cost. When changing my car, I use a simple spreadsheet to calculate cost of ownership over a period of years. The results are usually surprising.


I agree on total cost of ownership, Aitch. I don’t need a spreadsheet to know that keeping a car for a ‘long’ time is a cost effective approach as long as there are no major problems. The only real problems with cars that I have bought was when they were nearly new. In one case the engine had to be replaced due to a manufacturing fault and that proved very inconvenient.

I have driven many hire cars and an interesting variety of other vehicles, but enjoy getting back into my own car enjoyable because I have a much better idea of how it will handle. My car will do 60mpg on longer runs if I drive carefully and just below 50mpg overall, including many short runs. I have covered 72,000 miles in 10 years which is not much for a diesel. I might change it this year, but I certainly don’t find buying a new car much fun. Each to their own.

tahrey says:
10 August 2012

So a 7p difference in a roughly £1.40 overall cost (so, 5%) means diesel is suddenly so much more expensive than petrol that you will lose money by using it? Er… ok… let’s just quickly think this one through before we go writing a whole article about it.

Let’s say there’s an 8p difference, and the two fuels are £1.36 and £1.44 (4p either way of 1.40)… If your petrol car gets 34mpg (or, 25 miles to the pound), how efficient does the diesel one have to be to be exactly as cost effective? 25 x 1.44 = … 36mpg.

Two mpg better.

If your diesel car is only 2mpg better than the equivalent petrol, something’s gone badly wrong.

Currently I’m driving a diesel which – at about the same speeds on almost exactly the same route as I drove to and from work a year ago in an equivalent petrol model – gets 54mpg vs the old car’s 34mpg. Once you factor in the per-litre price increase (effectively reducing the diesel economy to 51mpg, on a fairly taxing commute), I can drive 50% further for each pound spent. In other words, it’s cut a third off my fuel costs. And I think the engine is probably not running anywhere near as well as it should, either.

It cost me about £400 extra vs what a like-for-like replacement for the written-off petrol would have (£2400 vs £2000), and driving roughly 7500 miles a year (~£1250 petrol, ~£840 diesel) I’ll be about ten quid in the black once it hits its first anniversary. £420 up by its second.

Really, this was a bit of a nothing idea as the difference between each fuel’s cost per litre when compared to the different in economy is so minimal that you can more or less ignore it.


That’s fine for an older car. Anyone buying a new or nearly new car should be more concerned about deprecation than mpg or cost of fuel.

54 mpg vs 34 mpg (an unusually wide differential) would mean 100 gallons or so for a 10,000-mile driver – say £600 p.a. Depreciation on anew car ranges between about 33% and 66% or worse over 3 years on new cars. On a £21,000 car, that’s a difference of £2333 p.a.

Buyers of new cars should choose the right model first and only then worry about petrol vs diesel. And of course there’s a great deal more to it than mpg and fuel price, e.g. maintenance, insurance, servicing, road fund licence, reliability,

It constantly amazes me that people fret as much as they do about mpg when there’s so much else to take into account. That isn’t to say mpg isn’t important, just that it’s only one of many factors.


Most of my experience of diesels has been in company cars over 25 years mainly Fiat mid range models. The journeys were long and each car did upwards of 100,000K miles. Almost totally trouble free and consumption close to 60 mpg.

Whilst for me the fuel consumption was not the issue, driving satisfaction was. High gearing gave relaxed motorway cruising while significant torque made acceleration and overtaking safe and easy. Being a high miler the prospect of accidents and fires was always present so it was good to feel that I was not carrying the most explosive fuel. One small point. Traveling in winter meant inevitable icy conditions and the ability to climb slippery slopes gently using no throttle using the torque got me out of a few tricky situations.


hi,i do 80 miles everyday for work. can any one advise me what kind of car do i need to be buy?
when i go work i pass 4 villages which is country route. please advise me what car please!!

Tony says:
14 March 2014

Auto fuels are an emotive issue because of the high cost in proportion to our incomes. Nevertheless, they play a key role in enviromental issues and one that must be addressed in a clear, sensible way. Changes will not be implimented overnight, whatever some people might want/believe.

Auto diesel is more effective (I did not say efficient) for reasons that have already been described above, most notably the higher energy content per weight and the fact that the diesel engine operates at higher compression ratios which makes in more thermodynamically efficient.

However, there are growning concerns over the health issues surroundin the combustion process of diesel. Accelerating levels of micro polutants in our cities (ALL cities) is direct consequence of the increase in diesel-engine vehicles. Put simply, petrol requires a very precise mixture of air-fuel ratio in order to ignite and when it does burn it is sudden and explosive. Diesel on the other hand will burn whatever the air ratio is. Less air and it burns poorly, producing vast quantities of unburn and partially burnt fuel. Because of the combustion characteristic, even the best-maintained and designed deisel engine produses a range of these particules durin gthe combustion cycle. YOu have heard of increasing use of “Particle Filters”, but this is only a method of dealing with the problem, not removing the problem. Petrol engines, especially the newer ones, are more effective in their combustion process but produce more carbon because they burn more fuel (same weight but more volume.

In essence, all fuels are hydrocarbons. We have gone from using coal, pure carbon, to oils a range of which have a varying proportion of hydrogen to carbon. Auto diesel contains slightly more carbon than gasolene (petrol), however, gas (LNG, LPG) has even greater hydrogen content than carbon. The move towards gas away from oils is a step in the right direction as it moves more toward the hydrogen end of the hydrocarbon scale.

However, we have to expose these “renewable” fuel oils for the sham they are. Vegetable-based oil stocks are even more carbon loaded (because they come from plants) but the real issue is the vast areas of the world’s vegitation that is being cleared in order to produce these so-called “renewable” oils tha tin the end are just as polluting as fossil fuels. It has the added (and worrying) feature of removing the world’s oxygen-producing “lungs” and hence reduces the ability of the world’s atmosphere to recover from natural polluting events.

Bear this in mind…… In it’s life a tree absorbs a vast amount of carbon from the atmosphere. When you cut down that tree and burn the wood, all that lifetime of carbon is then released. Any oil from the tree (or it’s fruit) contains the carbon absorbed in that time of growing and is subsequently released. Also, if a treee falls and lays there rotting, the decaying process also releases all the carbon trapped in the cells. Head they win, tails you lose. All the carbon gets release whatever way the tree’s wood is disposed of.


cb47 – When I bought a diesel car with a DPF a couple of years ago, the salesman did tell me about the need to do periodic longer runs at higher speed to allow the filter to function correctly. He gave me a leaflet. When I took delivery of the car, there was information about the DPF, how to avoid problems and what to do if a warning light comes on. As it happens, I have known about the potential problem for some time.

I follow the instructions and all seems well. Although I do less than 10k miles per year I prefer the characteristics of diesel cars and mine is returning over 60mpg including quite a number of short trips, such as 0.7 miles to the local supermarket as well as the longer trips at higher speeds needed to keep the DPF working. The inside of the tail pipe is still clean after two years. The only uncertainty is how long the DPF will last. Catalytic converters often created problems when they were introduced on petrol cars but they improved.

Obviously diesel cars are now unsuitable for users who don’t regularly do longer journeys but I don’t see that doing only 6000 miles a year need necessarily be a problem.


Oops. This was a response to post by cb47 below.


Hey, wavechange,
Interesting comments but what vehicle are you driving? I have checked with my local Mercedes-Benz dealer’s service guys & they have said they have not had any issues with DPFs. No other suggestions about maintaining the DPF were forthcoming & no info in the manual.
I’ve had my car for nearly six years now & it has just 43K on the clock, (had 24K when I bought it).
I also have a 1998 Ford Escort Estate, (petrol), that I use for local, stop-start trips, & visits to the local tip; the Merc gives better mpg & I’ve decided it’s time to stop mollycoddling it & use it more for everyday use. Your comments were helpful.


Its a Golf 6, 1.6, about two years old. I did not go for the more economical version that stops its engine in traffic because I did not know much about the reliability and I don’t often drive in traffic.

There are different kinds of DPF cleaning systems and I guess I have the one that injects extra diesel to burn of accumulated carbon, on the basis that the fuel economy sometimes goes down on a familiar journey for no apparent reason. That is a guess and I cannot be sure when a cleaning cycle is in progress.

I know that there is a warning light to show if it is necessary to drive above 40 mph continuously to allow a cleaning cycle to complete. That would not be difficult for me, but it has not been necessary yet. For the time being I will assume that just using the car as I do is OK. As long as your car gives a warning that action is needed to clean the DPF you can probably get away with driving as suits you, keeping the manufacturer’s recommendation in mind.

At one time I was interested in how cars work but they are now just something to get from A to B and hopefully back again.


In 2009 I bought my first diesel powered motor car thinking it the sensible option. How wrong was I? It was not long after that I first heard about Diesel Particulate Filter issues for those owners using their cars for short runs. I’ve still got my Mercedes-Benz C320 CDI estate but do ensure I give it a good run every week or so. My annual mileage is only around 6,000 so, basically, I bought the wrong engine type. I don’t believe the average buyer is aware of this potentially expensive DPF system & its inherent problems, & I’m sure the selling agent is not going to reveal such potential extra costs to the buyer!

PeterJ says:
1 August 2014

Petrol v diesel saga
I bought my Golf VW 1.6 diesel 2 years ago…. at that time government was still promoting diesel as the cleaner option. The VW dealer did NOT highlight what has been increasing ‘noise’ about the added particulates with diesel fuel, but stressed the better ‘economy’ of diesel engines. The AA (or was it the RAC?) stated last week that in a sense there was a government ‘miss-selling’ issue which led to encouraging 1/3 of UK drivers to move to diesel fuelled cars. Is there some cause to claim compensation from governments?