/ Motoring

Are diesel cars still cheaper to run than petrol?

If you had asked me a few years ago about whether a car is cheaper to run on petrol or diesel, I’d have said diesel without hesitation. But the scales appear to be tipping in favour of petrol these days…

I remember clearly the excitement at the Renault garage I worked for as a mechanic back in 1980, as the first Renault 18 diesel was delivered. I also remember the derision around the garage, the first time the engine was started – it sounded more Massey Ferguson than Renault. At that moment we all thought diesels would never catch on.

How wrong we were, and with the government soon reducing the duty on diesel, to encourage take-up of this inherently more efficient power unit than the gas-guzzling petrol engines of the time, sales soon picked up.

Premium upfront price for diesel cars

Carmakers took advantage of growing demand, charging a premium on diesel cars. This was justified because of the inherent efficiency of diesel engines compared to petrol ones, and because diesel engines have to be more robustly designed than petrol (to withstand much higher compression pressures).

They certainly seemed to be more resistant to failure than petrol. The comparatively simple mechanically controlled fuel-injection systems of the time were well developed and reliable, having been derived from the agricultural and haulage vehicles already employing them.

For a long time, diesel was the first choice for company cars and a growing choice for private buyers too.

The times, they are a-changin’

Back then, the premium to buy a diesel car could easily be offset against the lower fuel price and vastly superior efficiency. And there were added bonuses, when the tie between CO2 emissions and car tax meant diesel road tax was also cheaper.

But the fuel price differential was changed when the government equalised fuel duty and the price of diesel rose above that of petrol as a direct consequence. And the introduction of ultra-efficient lean-burn, super- and turbo-charged petrol engines has made another difference. These offer pretty good economy and a power curve much closer to that of a diesel, but without the seemingly ‘traditional’ premium still charged on every diesel by manufacturers.

It now takes some careful calculation to check which option is best. You have to consider exactly how quickly you can recover the premium paid for a diesel in fuel efficiency savings.

Petrol vs diesel costs investigated

For the first time, the market looks set to sell more diesel than petrol cars this year, so we decided to compare the running costs of petrol and diesel cars for the latest Which? magazine. I was genuinely surprised at how skewed things are towards petrol now.

Carmakers still insist on charging a premium for diesel, so with diesel fuel more expensive and huge improvements in both the efficiency and reliability of petrol engines, it turned out that in four of the six cases we considered, petrol was the clear winner.

For example, with a £2,370 premium on the diesel version of the Vauxhall Astra, we worked out that it would take nearly nine years (getting on for 100,000 miles) to recoup this in diesel fuel savings. In some cases we even found it could take 14 years to see savings!

If I were in the market for a new car, I would certainly check out whether buying a diesel would actually pay in the long run. But I know fuel choice doesn’t always hinge on cost. Emissions, refinement, noise and even towing ability can all come into play. So what really matters to you – are you a diesel or petrolhead?

If you were considering buying a car, which would be your top choice?

Petrol (40%, 211 Votes)

Diesel (29%, 154 Votes)

Petrol hybrid (10%, 51 Votes)

Diesel hybrid (9%, 46 Votes)

None - I don't drive (5%, 27 Votes)

Electric (4%, 20 Votes)

LPG (liquefied petroleum gas) (3%, 15 Votes)

Total Voters: 526

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Profile photo of wavechange

I prefer driving diesel cars and am prepared to pay a bit extra for the privilege. Over the 8 to 10 years I keep a car, the better fuel consumption helps offset the extra cost, and I would rather pay extra for an engine than some of the pointless gadgetry that manufacturers entice us to pay extra for.

Thank goodness that modern diesel engines are much cleaner than what we had twenty years ago, or we would all be choking in soot.

Prospective purchasers of diesel vehicles need to know that they could have problems with the particulate filter if they do frequent short journeys without the longer trips needed to keep the filter working properly.

peter says:
4 November 2016

is it worth paying premium price for diesels

Profile photo of wavechange

Hi Peter – It is more than four years since I posted my comment and a lot has happened since. A diesel particulate filter can be very effective in removing soot and the inside of the tailpipe of my car is as clean as when I bought it, over four years ago. Nevertheless, we are now aware that DPFs do not prevent emission of smaller particulates which may be more of a health hazard than soot. Another problem is that the move to more fuel efficient diesel engines has increased the emissions of nitrogen oxides, and nitrogen dioxide in particular is harmful to everyone, especially those who have respiratory problems. Vehicles currently have to comply with standards but these reflect standard test conditions rather than typical road use, where the emissions may be much greater than under standard test conditions.

Even if there are good reasons to switch to buying petrol cars, there are many diesels on the road and most commercial users use diesel. There have been undoubted improvements in petrol engines during the time I have been driving including electronic ignition systems, fuel injection, reduction and eventual phase out of organic lead compounds and the introduction of three way catalytic converters in exhaust systems. Perhaps we can continue to improve both types of engine.

I have been very happy with my diesel cars and have never had an engine fault, but petrol cars are reliable too if you look after them. I am also happier with diesel engines when driving, but that’s not doubt because I am used to them. Over the summer months I was getting a genuine 60 mpg, though this has fallen with the onset of cooler weather.

Profile photo of rich835

I’ve driven diesels for the past 10 years.
I believe it’s the best choice for me, as I do around 25,000 miles a year.

It’s the not economy so much that keeps me with diesels (I don’t think there’s an awful lot in it between petrol and diesel where that’s concerned nowadays), it’s more to do with the robustness of the engine and its potential long life compared to a petrol engine.

I’ve actually never had a diesel engine break down on me, the problem I find is with the rest of the car. Usually the engine will outlast the running gear, (suspension, steering and so on). These seem to be areas of cars which are not built to last. Nowadays things like brake discs are designed to wear out in parallel with brake pads, ridiculous. Bulbs are often impossible to change by yourself, also ridiculous.

Cars are deliberately designed in such a way that the home mechanic can no longer maintain them. It’s all a big scam to rip off the motorist that has no choice becuase he/she needs a car.

Sorry, going off topic now, but I could rant for hours on this….

QPR says:
18 July 2012

Diesels here for a long time, mostly all over the south of England but sometimes further. Had a chance to try a Nissan Leaf a while back and loved it. I think that’s the future. I did about 70 miles in it in various urban stages and it only cost a couple of quid (charged overnight in the garage). I wouldnt take it on the motorway, yet.

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The manufacturers will continue to charge a premium for diesel engines because diesel is still much cheaper than petrol in most European countries. Although car prices vary between European countries, diesel remains the cheaper fuel in general, so UK diesel car prices are unlikely to converge with the UK petrol car prices.

Profile photo of dean

You have to look at how many miles you do. With some of the comments here, diesel is absolutely the right choice for them as they do lots of miles every year.

I recently bought a new car and decided that diesel was not for me with as I drive under 10,000 miles per year. You also have to consider how long you will have the car. I have never owned a car longer than 2 years and I certainly won’t be keeping my current car any longer than that because it’s a new Mini and built as well as a 1970’s Rover.

I chose petrol due to the responsiveness of the engine and the price compared to diesel relating to my usage. Plus if you choose a small car (low weight) then you can save money that way too.

You have to add a turbo to get any performance though, my girlfriends car when up for renewal will probably have the VAG 1.4 TFSI engine with a super and turbo charger where you get performance and economy.

Felix says:
18 July 2012

I belive that with automatic cars there is a completely different story. I have a Mitzubishi Colt (2008) automatic one and I am happy with its consumption. (around 55-60 mpg). Not sure if there is an automatic petrol care that would have the same consumption.

Profile photo of wavechange

At the time of writing, the poll votes include Electric 1%, 0 votes.

The Which? computer may need oiled. 🙂

Profile photo of wavechange

In case anyone wonders what I’m talking about, it’s fixed now.

David Lucas says:
19 July 2012

Surely not just £ costs should be considered but also the comparative CO2 emissions of the two types of engine, also the emission of micro-particles by diesel engines (especially below 2.5 micrograms size), which I understand are strongly implicated in lung diseases and mortality. Regarding these particles, I understand that particulate filters can trap these, but that (as stated in a box item linked to the Which? article), these filters get blocked if cars are just used for short urban journeys.

wornout says:
20 July 2012

When buying a new car ten years ago I worked out that the difference between cost of the car and the cost of diesel, it would take me 7 years to break even if I purchased the diesel and I did a fairly high mileage in those days. Diesel was so much cheaper in those days too. I am surprised it has taken Which so long to do such a comparison.

Helikaon says:
20 July 2012

I’ve been driving diesels for 3 decades, plus motorbikes and now a Mazda MX5 petrol car. I prefer diesels as does my wife, for the solidity and driveability. I must admit I’m in a quandary over our next purchase. Our old 406 Peugeot HDi estate has done 175k miles and we plan to replace it with a Ford Kuga Titianium. A 1 year old diesel was a no-brainer but I’m having second thoughts. We’ll do less than 10k per year, the particulate filter could cost a fortune to replace and the 2.5 petrol model is a lot cheaper (and rarer). I doubt the cost of the latter’s depreciation will be so different to compensate buying a diesel. Times they are a changing

JPD says:
20 July 2012

I have just read the article in the August issue of Which and find the information very misleading. To take the fuel saving against the new list price delta is not a representative measure . . . much more should be considered, which is touched on in the closing paragraphs. The diesel car will still command a resale value premium over the petrol. The resale value of the Fiestas 4 years from new, assuming average mileage and condition, would be £5089 for the diesel versus £4198 for the petrol . . . so the premium for the diesel over 4 years is actually £1509 rather than the new price delta of £2400. This is a considerable difference and has a dramatic effect on the payback period. The road tax for the petrol car over 4 years is £400, the diesel costs nothing . . . hm, now the premium is £1109

Significant contributors to the premium that one pays for a diesel car are the costs involved in making the diesel engine and the additional after treatments that have removed the ‘dirty diesel’ stigma from back in the mists of time . . . there is no manufacturer conspiracy.

The consumer’s expectation for high levels of safety and specification make DIY maintainable difficult. I would much rather crash a top spec 2012 fiesta with all the additional ‘stuff’ that we have all come to expect such as ABS, air conditioning, power steering, great fuel economy, a plethora of air bags, bluetooth, and a Euro NCAP 5 star etc (none of which work without a load more kit on the car, and in particular under the bonnet) than a MK1 1970’s vintage Fiesta with loads of under bonnet space and an agricultural 1600 cross flow engine and a medium wave radio . . . hey but maybe that’s just me!

James says:
22 July 2012

JPD, I agree. Why do people always miss this? The cost of a car is not its price, but its depreciation and running costs. Of course you do need to be able to pay for the car, either outright or by some use of finance, but that should always be only one of the considerations.

Profile photo of ChrisGloucester

Yep, I think it might well be “just you”.
I’d also shop around a bit, in my experience the price difference in 4 year old cars (diesel v petrol) is much smaller. But I’d agree there won’t be much if any economy benefit of new cars, again petrol v diesel. On the otherhand my calculations suggest a 4 year old diesel will be a cheaper owning experience if you do average mileage.

J.D.Baines says:
23 July 2012

While one accepts that ‘miles per pound’ probably is in favour of diesel, only a few in this debate have gone for the health side – almost all is on economics.
The increase in the use of diesel fuel in the last 30 years seems almost to parallel the increase in the incidence of children’s respiratory problems including asthma and chronic bronchitis.
Is it not time that the economy/health debate should go head-to-head?
To benefit the economy and energy-use diesel should be encouraged BUT to benefit the health of the population diesel should be discouraged.
Increasing the fuel tax on diesel and reducing it on petrol by the same amount would be cost-neutral as the usage is roughly equal, and would greatly benefit the individuals living in rural areas where public transport is negligible and diesel cars are too expensive.

Profile photo of wavechange

I am an asthmatic, and developed this condition as a child, shortly after moving from a village to the suburbs of a city. I’m sure that pollution was a major factor and until a few years ago I had breathing problems in large city centres.

Sulphur dioxide is a problem for asthmatics, but this has been largely overcome by introduction of low-sulphur fuel.

Particulate emission by diesel vehicles is much less than it used to be. New vehicles are being fitted with diesel particulate filters which do make a big difference to smoke emission. Unfortunately, there are still a lot of dirty diesels on the road.

A few years ago I would have agreed with you. Now, I would prefer to see efforts being made to cut down the amount we use both private and public transport. We seem addicted to transport.

Dave S says:
23 July 2012

I guess if you run an artic, a taxi, or you never go anywhere without your caravan, you’d probably want to go for diesel. For any other purpose I can’t think why you would. The downsides of diesel include the awful smell, the bizarre power delivery characteristics of a turbo-diesel that make it so easy to accidentally spin the wheels at 5 mph but runs out of puff at 3,000 rpm, just when you really need to complete that overtaking manoeuvre, and above all else the noise like a bag of spanners in a tumble drier. So many articles point out that diesels are so much quieter now, and can barely be detected in the cabin, and to an extent that’s true, but the noise outside continues to be alarming. I saw (and heard) a lovely new Jaguar XF which clearly had a big diesel under the bonnet taking off at a very fast lick from the M6 tollbooths. Looked lovely but we had the window open to pay the toll, and this beautiful car sounded like a Transit van on steroids. Even my wife looked at me and asked “What was wrong with that car?”

I run an A6 with a 3.2 litre petrol and after 146,000 miles it’s still luxurious and with a creamy power delivery that builds smoothly all the way to the red line, and still gets 32 to 36 mpg. My wife has a new Scirocco with the marvellous 1.4 TFSI engine with turbo and supercharges. It’s incredibly nippy, but very frugal, although probably wouldn’t be good at towing a caravan!

Lisa says:
23 July 2012

My previous car, which I had for 17 years was a diesel and I never had any trouble with the engine. I would still be using it, but due to a shoulder injury I needed power steering so had to reluctantly change.
My new car I bought in 2009 and is also diesel. It has a very small tax charge, and perhaps because I don’t need to use it in the town for shopping, it is very comparitively cheap to run. I live in a small market town , so use it mostly to travel between 10 to 60 mile journeys to the surrounding local places which of course have no public transport and the car is the only way to get to them. With the exception of a couple of extensive journeys a year, my fuel bill is about £50 every two months.so I find diesel a good choice rspecially as the engines seem very reliable and long lasting.

Profile photo of ChrisGloucester

There is no clear answer to this question, it depends on several variable factors. Buy a new car, keep it only three years and do modest mileage and you’ll find the diesel models higher purchase cost means no savings will be there.
However many of us buy used cars. The purchase price difference is nothing like as big and especially if you do average or above average annual mileage the diesel will work out cheaper. Add to this that diesels engines tend to last longer than petrol and you’ll find that secondhand diesel is a good buy.
Diesels have come on a lot in recent years and are much less like the “tractors” they use to be but still many prefer the smoother petrol engine. If you want diesel economy and the smoothness of petrol try an LPG car. I have one and would have another, 71p per litre but admittedly lower MPG. Still works out at under 10p per mile fuel cost and, if you run out of gas it will still run on petrol.
I’d say that compares well, but you of course have to buy a car already modified to run on LPG, a £1500 to £2000 retrofit leaves you with the same comparison problem.

MrsBee says:
26 July 2012

These calculations really only work if you only ever drive in the UK. We drive all around Europe and diesel is consistently cheaper than petrol. It would have been useful to point this out in the article. It was a major factor in our choice of a diesel estate.

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For the high mileage drivers diesel seems to be the clear winner – provided you don’t think anything matters except money. Unfortunately there are no clean diesels yet – the existing cleaner diesels still emit lots of invisible particulates that petrol engines don’t, and many still emit NOX pollutants that cause illness too. These invisible particulates turn up in inside our tissues – even getting into the brain. As a result of health concerns, there are tighter emission standards on the way for diesels that are likely to increase their initial cost and reduce mileage as filters and reduced compression ratios come in. The present ones are likely to be allowed to carry on killing until they wear out, unfortunately. In case you think this extreme, bear in mind that air pollution in London, most of it from diesel, kills about twice as many people each year as road accidents in the whole of the UK. They just die out of sight. Especially in cities, electric cars, buses and taxis can’t come fast enough. It’s much better to clean up our power stations than to try to clean up each vehicle.

Thomas Tait says:
30 July 2012

My experience is based on E Class Mercedes cars which which give far greater benefit for the Diesel model than your article would suggest. Not surprisingly, Mercedes sell more than twice as many Diesel than Petrol cars of the same model. Instead of new Diesel cars being dearer, they are in fact cheaper to buy. The cost of fuel may be 3% higher, but the fuel consumption of the same size engine is 30% less for the Diesel car. Instead of taking many years years to recoup the higher cost of the Diesel car, the benefit is immediate, even for low milage use.

Mark says:
1 August 2012

One obvious flaw in this analysis is not to consider the residual value of the respective cars. It would be interesting to see how these compare.

Stan Isles says:
14 August 2012

Several people have commented that diesel in Europe is cheaper that in Britain, one garage in Germany last month was selling diesel for 1.40 Euros and petrol for 1.56 Euros per litre, this might be an exception, but all garages I passed in Germany, Belgium, France and Spain petrol was considerably dearer.. If these differances were repeated in the UK then surely there would be no contest between petrol and diesel cars. When I first bought a diesel 8 years ago diesel was cheaper. What changed to make it dearer than petrol other than the fuel companies greed?

DaveSuffolk says:
25 August 2012

I find all these comments about fuel economy slightly amusing, because we waste fuel in so many other ways – by making uneccessary journeys to the shops or school run, by not switching off the engine while waiting in a queue, by carrying uneccessary weight in the boot or not keeping the tyres at the correct pressure. Not to mention erratic driving and braking. Why can’t we just accept that cars cost a lot of money and the little you save on fuel is a drop in the ocean? I drive a diesel because I like it, I like the easy mid-range overtaking, the fact that at 30,000 miles it runs better than it did when new, the low revs at cruising speed, and the extra engine weight to help get traction in the snow. It doesn’t smell and inside the cabin it’s not noisy. I think the price difference to petrol is unjustified and unfair, but as long as it doesn’t get too much worse I’ll buy another diesel next time.

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I agree, Dave, and I could add a list of other ways of saving fuel and money. My favourite is to combine visits to places rather than do several out-and-back journeys. It does not worry me that my car sits on the drive for one or two days a week.

I hope you are not planning to replace your car soon. At 30,000 miles, a diesel is just about run-in.

Richard says:
27 August 2012

In my limited experience modern diesel engines are less reliable than petrol. However, I suspect it depends upon the type of use they get. Traditionally diesel engines were considered better than petrol for short journeys. Since the development of low lag turbo engines I think this may no longer be the case.

Six years ago I bought a new Skoda Octavia with the 2 litre TDi engine. With under 50,000 miles on the clock I started to get a problem whereby the engine would suddenly lose power, often at an inconvenient, sometimes dangerous, moment when you need the power. Without displaying any warning light the engine management system would go into a ‘get home’ mode and disable the turbo boost. Stopping the engine and restarting would reset the engine management system and normal power would be restored. This gradually became more frequent to the point where it would happen on most journeys.

I was told that the turbo was probably at fault due to carbon deposits preventing the variable vanes from adjusting freely. Apparently carbon can build up if journeys are short and/or are at low speed.
A Skoda franchise garage estimated a replacement turbo would cost in the order of £1,200 fitted. Fortunately I managed to have the turbo reconditioned through a non-franchise garage for a fraction of that and it’s rectified the problem. The garage told me that a reconditioned turbo should last as long as a new turbo. They said that they recondition a lot of these turbos for the local taxi companies and that the problem isn’t confined to the Volkwagen Audi Group – it’s a general problem with the variable vane technology which is designed to reduce the lag associated with traditional turbos. I understand that carbon build up is not a problem with these type of turbos in petrol engines.

Since then I have had to have a new throttle body because the butterfly valve system failed.

My two cars prior to this diesel were petrol – one was a 6 cylinder, the other a 4 cylinder turbo. I had both from new and kept them to over 100,000 miles. Apart from both requiring new batteries (as you might expect), the engines were faultless.

If you do a lot of long distance driving then diesel may be for you. I don’t. My next car will be petrol!

Profile photo of ozzie

In my opinion I think diesel engines last a lot longer than petrol engines, I had a 2002 diesel Mondeo which had 127,000 miles on the clock but showed no sign of wearing out or loosing power, I reckon its new owner will be able to get another 127,000 out of it.
Question: It has been reported that diesels will be obsolete in 5 years time, is this true?