Diesels less reliable than petrols and pricier to fix, report claims

Diesels less reliable

As if diesel didn’t have enough on its plate, now experts are saying that cars powered by the fuel are less reliable than petrol motors. The majority of complaints around diesel have been down to its environmental credentials. However, a new report shows that diesel cars could be three times more likely to break down than their petrol equivalent and up to 20 per cent more expensive to fix.

How unreliable are diesel cars?

Car maintenance firm MotorEasy, which specialises in aftermarket warranties, studied 30,000 cars between the ages of three and eight years old. It found that diesel models were less reliable than petrol cars for seven out of 10 car makers (71 per cent).

Which diesel cars are worst?

According to MotorEasy, Alfa Romeo has the worst reputation for reliability with a failure rate of 47 per cent among its diesel models. That makes them four times more likely to fail than one of the Italian firm’s petrol cars. It’s followed by Land Rover on 41 per cent and Mitsubishi on 36 per cent. Saab and Mazda, both on 33 per cent, complete the bottom five. Kia and Mercedes are next with a 29 and 27 per cent failure rate. Vauxhall, MINI and Audi make up the remainder of the top 10, all on 26 per cent.

Diesels less reliable

Diesel Alfa Romeos such as the Giulietta are said to be 47 per cent more likely to break down than a petrol equivalent (Picture © Alfa Romeo)

Which diesel cars are the best?

Ironically Volkswagen, the brand that helped put diesel in the emissions spotlight, is one of the better manufacturers. And its Czech brand Skoda, which uses VW technology, was the best in the study. Just nine per cent of its diesel cars fail.

Why are they less reliable?

Petrol relies on spark plugs to cause the explosion in the cylinder that turns the cranks to eventually power the wheels. Diesel can’t do this because it is less flammable. As a result, diesel cars use what’s known as compression ignition. This prompts the explosion by putting the fuel under enormous pressure. It’s these high pressures throughout the engine that cause failures in components such as seals.

Why are diesel cars more expensive to fix?

The report says fixing a duff diesel could cost 20 per cent more than the equivalent repair to a petrol car. The average diesel car costs £517 to fix while for petrols the prices is £433. Diesels are more expensive because they operate under such high pressure. This requires fine tolerances and sturdier parts.

How to protect against a diesel failure?

The overarching advice to any car owner from Green Flag’s technical expert Nick Reid is to always stick to a car’s service schedule. This will ensure that many potential problems are nipped in the bud before they become catastrophically expensive. He said: “As an engine requires a lot of parts to move in perfect synchronicity, if you have a problem with one perhaps relatively cheap component, it can quickly escalate and become a very expensive failure.”

The advice from MotorEasy is to consider mileage if you’re looking at used diesels. Matthew Tumbridge, MotorEasy COO said: “To be clear: avoid diesel cars with over 100,000 miles on the clock. They will cost you money, time and hassle. Of course there are exceptions to every rule. But it isn’t worth taking a chance with these vehicles. If you must buy a high-mileage car, buy the petrol model with the largest engine.”

Drivers who cover low mileages around town should also avoid diesels as the Diesel Particulate Filter (DPF) is prone to clogging. Read more about this here.

47 comments on “Diesels less reliable than petrols and pricier to fix, report claims

  1. MATTHEW 12/02/2018 1:33 PM

    What a load of rubbish a 100,000 mile diesel engine is virtually just run in!

    • Ray Wheeler 18/04/2018 8:30 PM

      yeah such rubbish ,had my peugeot from 3 years old 03 plate ,it passes the mot every time no problem . starts and goes same as day i bought it.,and it don`t smoke either.

  2. terry harris 16/02/2018 9:45 PM

    a rubbish remark diesels are mote reliable, ive had them both, prefer diesel anytime,

  3. Graham Riches 24/02/2018 9:27 PM

    Find it difficult to accept what I have just read in your article regarding Diesel cars being less reliable than petrol. Since 1989 I have used diesel engined cars and driven in excess of 1.5million miles in 8x Peugeots, a Renault (for my sins and never again, the most unreliable!) 2x Jeep, 2x Mitsubishi, a Honda- poor reliability and currently, 3x Kia by far the most reliable all round with 200K todate. The most miles driven in one of those vehicles was a 1996 Peugeot 406 2.1diesel was 220K and the engine never once let me down or missed a beat. All my cars are serviced at manufacturer’s recommended mileage. Where do these supposed facts come from, I’ve never been questioned ? Not looking forward to having to use petrol engined car.

  4. Kenneth Harman 11/04/2018 7:45 PM

    What utter rubbish!! I have a VW 2.4 diesel campervan, toured Europe for 1 month last year, will do the same this year, and it’s on 235.000 miles, and still going strong!!! What will the experts say to the French, where 85 to 90% of cars there are diesel

  5. Chazzer 11/04/2018 8:14 PM

    Quite frankly the comments on diesel car ownership/reliability is a load of TOSH.
    And is just adding more confusion to the already “Muddied” waters on diesel vehicles and the lack of clarity from both the government and other motoring organisations.
    Do us all a favour and stop SCAREMONGERING. Suggest you get your facts from a more reliable source.

  6. Brian Whitby 12/04/2018 8:25 PM

    Diesel engines are known for their longevity of life and better fuel economy than petrol. The higher compression used in a diesel engine requires much more precision engineering. Therefore, as applies to all engines, providing scheduled servicing is carried out, diesels can run for hundreds of thousands of miles. Ask the question, why aren’t HGVs using petrol engines? This is a biased report because deriding diesel vehicles is ‘flavour of the month’.

  7. Julie Harries 13/04/2018 6:56 AM

    I have driven hundreds of thousands of miles in VW diesels over 30 years and have never been let down. Apart from VW lying to us all that is

  8. Trevor Jones 13/04/2018 11:05 AM

    Scaremongering tactics. I had petrol cars for 20 years and they were constantly breaking down. Had diesel cars now for over 15 years and not one single breakdown. No matter what government or these so called green people nuisances say I will always have a diesel car and a diesel motorhome

  9. Rowland P 13/04/2018 4:52 PM

    Started driving diesel cars over 30 years ago because they are more sturdy and a no-brainer because they are far more economical. Had a Citroen Picasso which went well over 200,000 miles before I sold it still running perfectly on its original injectors. However, I believe that they have become much more complicated in an effort to “clean” them up and the resultant technology causes lower reliability, not to mention the plethora of extra electronic gizmos which may be prone to faults.

  10. Geoff 13/04/2018 7:59 PM

    I agree with the other comments; I have had several of both types of car and to be honest apart from mpg in diesel’s favour I have found neither to be more or less reliable than the other.

  11. Pat Pat 13/04/2018 8:30 PM

    I’ve had three diesel cars that all had fap box and partial filter failures – very expensive to replace – due to the fact I don’t do heavy mileage or thrash them – something the garages all said was necessary to prevent the filters blocking. I now have a petrol car and although it isn’t so good on fuel economy, I’ve had no problems with it at all.
    Diesels are made to work, not use as a runaround or for town driving. I know several other previous low mileage diesel owners that have ditched them for the good old petrol engine due to the same problems as me. Manufacturers need to sort this anomaly out.

  12. Andrew Mawdsley 14/04/2018 6:52 AM

    I disagree ,not entirely with the comments.i am a motor vehicle mechanic owning a buisiness for over 30 years.i have seen the change in the diesel engine technology in my time whilst the principle of combustion remains the same the “add ons” to reduce emmissions are the most likely components to fail due to mechanical wear or electrical failure.the “high pressure” comment in the article is incorrect.the pressures in the crancase in both petrol and diesel engines are similar so the chances of seal failure are equal to both engines.the pressure in the cylinders are different, whilst diesel will require over 500 psi, a petrol will require 300 psi to run correctly. The metal componants in both types of engines are quite capable of these figures.the article is clearly missleading..you also need to factor in the mpg saving of the diesel engine against the cost of repairs.missfueling is the biggest cause of problems

  13. Douglas Tomlinson 14/04/2018 7:11 AM

    This article is irresponsible. It is certainly not my experience that diesels are less reliable. What are the details of this so called survey? Is the evidence statistical or empirical? It looks to me like the poor results of Alfa Romeo has distorted the results for all diesels. Take Alfas out of the equation and what do make of the results then? Statistics can be manipulated to support any argument.

  14. Paul 14/04/2018 5:32 PM

    Have you ever considered that people who know they may have purchased a duff diesel vehicle may be more inclined to take out cover for it. Let’s face it they know they cost more to fix, and this would sway results of the study

  15. jIM 14/04/2018 7:43 PM

    You people are talking total rubbish about diesel cars been unreliable,They are more reliable than any petrol engine car and are far superior in all ways. far stronger engines more pulling power cheaper to run, more miles to the gallon give off less pollution than petrol cars ,( no matter WHAT THE GOVERNMENT CRONIES SAY!!!! ).

    • Mark Gaucher 20/04/2018 4:18 PM

      For me this is perfectly true. Modern Diesels (Euro 5 in particular) are a load of rubbish. we do about 10000m a year in our golf 1.6 TDI. So far it has required 3 EGR valves, 1 Turbo Charger and 1 Clutch at 14000m???? It requires Shell V-Power at £1.35/l and still seems to regenerate the DPF filter every 5 minutes, where upon it runs like a pig for half an hour and smokes like buggery!

  16. Kev 14/04/2018 10:42 PM

    I bought a brand new Ford Kuga and, as a diesel driver for over 25 years ( following Government advice) and had the 2 litre diesel version. A month after the warranty ran out the dual mass flywheel fell apart taking with it the clutch and starter. For a £28k car, a bill of over £3k a month after its 3rd birthday was not very impressive. At least it manages 40mpg. The current hate campaign has now dropped its resale price to that of scrap, so my next one is sadly going to be petrol. The other car in the household, a Hyundai i10 auto with a tiny engine just drinks petrol but at least it keeps going despite its obvious greater generation of pollution.

  17. Stephen Binks 15/04/2018 8:08 AM

    Like everything it depends on how you use it and how you look after it.
    Go to the shops three times a week, buy a petrol car. Sit on the Motorway for 100 miles every day buy a diesel.. Manufacturers service intervals are to make their cars look good to the Fleet buyers ie: lower pence/mile servicing. If it’s your own car cut the service interval in half and you have no trouble.
    Some people could break a wood burning stove …. especially if it’s a company stove made by BMW Audi or any of the other stoves favoured by the ‘rep’ brigade.

  18. Dave Wedd 15/04/2018 11:01 AM

    Total rubbish. I’ve been driving diesels since the late 1980s, and the engines have alway slasted for at least 250,000 miles. The cars have been replaced due to body and suspension wear, or the driver’s seat wearing out, or just wanting a more modern car.
    The only persistent engine problem was on a VW diesel that I bought with 170,000 miles and it would often refuse to start when warm. At about 250,000 miles I left in on my forecourt after buying another diesel, and then the fuel tank started leaking so I had to replace the tank promptly. That’s when I realised all the unreliability was due to rubbish from the fuel tank. With the new clean tank it went much better and stopped smoking too. The problem was nothing to do with being a diesel.
    Another diesel with an “engine” problem was due to water getting onto a sensor in the air intake, putting the engine management into limp mode. An engine management fault, not a diesel fault.
    My current Skoda diesel is getting a bit difficult to start in very cold weather, but that will almost certainly be a faulty glow plug, which can be replaced almost as easily as a spark plug. At 150,000 miles that glow plug will have lasted longer than the air conditioning pump did.

  19. Richard Hornsby. 15/04/2018 4:26 PM

    I agree with everything you four have said, diesels are far superior

  20. Bert 15/04/2018 10:18 PM

    My old ford focus diesel estate had 194,000 when i got rid of it ,never had a issue with the engine .the key is regular servicing.

  21. Anthony Sergeant 16/04/2018 5:05 PM

    What a lot of rubbish. I’ve had both Petrol and Diesel cars and always found deisel to cheaper to run and more reliable. As for the 100,000 miles and to avoid. The engine is just broken in at this point. Funny how all these horror story’s emerge when the government wants them off the road. I remember they done this with Petrol when the wanted everyone to use Deisel. I won’t be changing mine in the future for a Petrol regardless of This rubbish.

  22. AJ 16/04/2018 8:05 PM

    1. Average compression ratio for a petrol engine ~13:1. Average for a diesel ~20
    :1 so pressure in cylinder very roughly 50% higher than petrol. Not an enormous difference.
    2. LOT less to wrong in a diesel, no plugs, distributer etc. Granted glowplugs.
    3. Think some bright spark (pardon the pun) should sort the particulate emissions problem with nano tech.
    4. Thermodynamically, The diesel cycle is known to be far more efficient that spark ignition engines.
    I could go on … and on.

  23. Mike 17/04/2018 1:05 AM

    I have a Volvo diesel estate and it’s done 140000 miles . Runs perfect. Petrol engines are prone to flooding, damp starts. Spark plug failures and the new petrol engines using coil packs are always breaking down . For me , I’ll be driving a diesel until the government ban them off the roads.

  24. Nigel 17/04/2018 11:32 AM

    I have to say I have had a Citroen C8 diesel for 12 years now and done 240,000 miles. The engine itself has never ever failed. The only problems I have had (and there have been many) have been with the electrics.

  25. Frank 17/04/2018 6:53 PM

    I also agree with your other reports.I have owned five Yaris diesel cars with no engine faults and a Peugeot camper van, the only fault,one glow plug failed.Two company ford cars with many miles on the clock with no engine faults, Finally my latest Yaris diesel is FREE road tax proving lower emissions than the petrol engine. I feel we have a conspiracy against the Diesel engine.

  26. Roger Clarke 17/04/2018 8:15 PM

    How dare you insult our intelligence. I have been driving for 60 years and know diesels inside and out. and petrol cars. If you want speed use petrol, if you want reliability use diesel. The biggest problem in later years has been technology letting this side down, , all the sensors.and engine management and that applies to Petrol as well. But still use diesel over anything else. And as for the most likely to break down. Mitsubishi and Toyota have to be the best followed by all the Japanese. the worst being VW and Mercedes. Never tried Alfa so would not comment on the. I think your information STINKS. Roger Clarke

    . .

  27. Derek mcroberts 18/04/2018 12:43 PM

    Have had diesels with up to 200000 miles in the last few years, no problems with any of them, try pulling a caravan with a petrol engine, it will drink fuel. Would never buy another petrol engine. Total rubbish article.

  28. Ray Stevens 18/04/2018 4:34 PM

    never heard so much rubbish, diesel engines are far more reliable than petrol engines, my first, second, third car were petrol driven… then diesel engines came along government wanted us to change to diesel .. i have never looked back, i owned 5 Mercedes Sprinters, all did in excess of 200,000 miles reliable cars i have had 3 Mercedes Cars all owned for at least 7 years Mot No problem, engine reliability Excellent and they were all diesels, the last Mercedes was an Avantgarde A200 very reliable 90,000 miles only part exchanged it as i wanted a 4 x 4 that was a mistake, returned the 4×4 to the dealer and got my Mercedes back smashed to bits compliments of The Welsh Dealer in Neath,reluctantly gave it away due to damage as i had already purchased a Peugeot 3008 Diesel 1.6 which had an issue at time of purchase but felt it was worth spending what ever it took to get it right shame it took main agents 3 attempts at my cost when i had already told them what the fault was, Now its a great Diesel car to drive and i will NOT go back to petrol engines….

  29. Ron Cornell 18/04/2018 5:47 PM

    My Mercedes C Class Diesel is now on 160,000 miles, I have it serviced each time it is due by an independent MB garage. It drives like new and returns 55 MPG.

    I am fed up with this diesel tosh. It;s the best fuel and best engine, Every anti.. get over it!

  30. madmitch56 18/04/2018 8:02 PM

    Well, I am an ex Black Cab driver and I can honestly say that you are talking out of your exhaust pipe if you think Diesels are less reliable! My last cab was powered by the Nissan TD27 engine and when I gave it up, that cab’s engine had over 300,000 miles on the clock and all it had EVER had was regular servicing, an alternator and a water pump! Furthermore, I have been a Driving Instructor for the past 11 years and have ALWAYS used Diesel cars as Petrols do NOT take the punishment of the job for long. Honestly, you are fooling NOBODY with this!

  31. madmitch56 18/04/2018 8:11 PM

    Utter Rubbish! As an ex Black Cab Driver and now Driving Instructor I know how good a Diesel is. You cannot beat them for their ability to work. If Diesels are so “unreliable” “costly to fix” “More likely to break down” etc,Then how come there are NO petrol driven Farm Tractors? Or Railway Locos? Or trucks? Or Fire Engines? When I gave up my old cab, (it was powered by a Nissan TD27 engine), it had over 300,000 miles on the clock and was STILL regularly giving 36 mpg. It was the vehicle’s BODYWORK that let it down, NEVER the engine, which apart from regular servicing, had only EVER had an alternator and a water pump in all those miles. You are fooling NOBODY with this unashamed toadying to Government propaganda!

  32. John 18/04/2018 9:03 PM

    I love my smelly stinking Diesel car, I like others have driven both and found that Diesel is KING, it seems every time some big wig comments on topics like diesel sales go down and jobs are lost and the government have to hand out unemployment benefits, oh by the way the loss in car sales is due to brexit, to cover up there balls up on diesel, don’t we have some very intelligent big wigs in parliament, now they are blaming the cows for global warming they are farting to much.

  33. Keith Thompson 18/04/2018 10:24 PM

    Lets face it the Government is hell bent on killing off the diesel engine, and I believe this is just another piece of scare mungoring propaganda fed down from the Government. I have had three diesels and have been very happy with them all.

    • Harry Jackson 01/01/2020 9:00 PM

      I think your finger is right on the button, the article is issued merely to try mislead the general public.
      Yes modern diesels have more technology to combat the emissions problem and this technology is creating reliability issues, but it is not the Diesel engine that causes the problems.
      I have a VW T4 with 2.5 TDI 102 bhp, it returns 38 to 41.5 mpg even with 179k on the clock, I also own a s/h VW Touareg 3L V6 with 26 K on the clock, I could drive the T4 forever, everything is so good, change oil and filter at 1/2 time, the Touareg is still a babe and tows a bigger load than the T4 and has been a great car so far, although I believe they can be an expensive item to fix when they go wrong.
      I am 73 and hope I can end my motoring days with my current VW diesels and petrol Honda and Velocette Motor bikes.
      I think we are being fed dodgy data on electric vehicles by many groups brainwashed by the green lobby,
      When I think about the unreliability of electric hand torches ( never had one that lasts more tha 2year), I just do not have the confidence in the electric produce, plus the costs are horrendous.

      For me cars and vans have to be fuelled by DERV to make for all around efficient, powerful and happy motoring.
      Have a great 2020!

  34. PETER MALIN 19/04/2018 9:26 AM

    As a fairly new customer of yours I am staggered why you should be advocating the use of petrol cars against diesel cars as this would mean you would be involved in many more very expensive recovery trips. Two local garage owners told me that actual engine failures of diesel engines were about 85% LESS than petrol engines. In most cases it was the cars electrics which were at fault. Why would lorries,ships and trains only ever use diesels ? In your case I would ignore government and eco pressure groups and make NO COMMENTS on this issue and just hope your clients opt for diesel vehicles and so save you from paying out on recoveries.

  35. Colin merriott 19/04/2018 7:38 PM

    Total bull! I’ve had both over decades of driving and found zip wrong with Diesels, but had two petrol engines catch fire, and fall apart after 4 years, whilst I’ve kept one derv for 6 years without a fault! Long live diesel cars. As an extra, all hear of how derv is so polluting, but that is for old ones, old busses, etc. But know one really knows what the modern additives to modern petrol will have on us or the environment, as it took decades to nail down what was causing the health problems, lead in petrol, this was stopped rapidly, let’s see shall we! What happened to the big future hydrogen engine?

  36. R Foort 19/04/2018 7:39 PM

    Only ever had 1 diesel car. A Vauxhall. Astra estate. Every time we had to have something replaces in the engine it was a lot more expensive for the parts

  37. Fraser 19/04/2018 7:40 PM

    This article is incorrect and a complete work of fiction! It’s absolute rubbish.

  38. Anthony Mason 19/04/2018 9:56 PM

    Modern diesel engines are complicated with all emission stuff now added never skimp on servicing but saying don’t buy a 100k miller is talking nonsense The main worry with any 100k mile car is if it’s fitted with a dual mass flywheel clutch if it’s been replaced your fine but has not try to get the car as cheap as possible and keep a grand under the matress.

  39. Nigel 20/04/2018 1:24 AM

    I currently drive a Toyota landcruiser with a 3 litre d4d engine at 184,000 miles it still runs as sweet as a nut and I couldn’t wish for a better vehicle, its never missed a beat and for 16year old car I had to have a solitary drop link relaced for its Mot. I have to wonder at this governments witch hunt against diesel motors, call me suspicious but I see it as just another excuse for generating extra revenue and pushing older vehicles off the road therefore pricing some drivers that can’t afford newer vehicles off the road

  40. John Bennett 21/04/2018 6:32 PM

    Scare mongering again. Diesel engines, because they have to be made to finer limits than petrol will always, if serviced to the book, last longer. What may let them down is the electronic control units.

  41. John Murphy 22/04/2018 8:20 AM

    I have just spent about two weeks researching into a replacement for my 2008 E Class Mercedes Benz 220 diesel and am totally mystified at all this talk about the Diesel engine.
    My car is £220 for road tax, the equivalent unleaded petrol is £400 – £500 per annum.
    I can update my car for a newer equivalent diesel with road tax between £20 -£120 and get a better fuel consumption with the 7 speed trip trip tronic gear box thus cutting emissions.
    In the end I have spoken to my local independent MOT Station at length and we have agreed as long as the car is serviced properly by Mercedes Benz as and when it should then there should be no issues with emissions.
    The car has covered 100,000 miles and still ticks like a Rolex Watch so it will be resprayed and given a full overhaul and continue for another 100,000 miles.

  42. john gilbert 24/04/2018 9:02 PM

    It is amazing that despite companies such as Peugeot having Adblue technology to clean up the emissions the government take no notice of this fact and class the cars the same as all the diesels that do not have the technology

  43. D king 25/04/2018 6:01 PM

    Total rubbish. I have a diesel Peugeot 18 years from new and a diesel Alfa Romeo. Now 13 years old. The most reliable cars I’ve owned. Please don’t knock the poor diesel.

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