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

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.

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.

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

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.

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.

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…

rogerjp

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.

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.

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.

Dean

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.

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.

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.

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.

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.

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.

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.

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.