/ 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?

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?