Which is more reliable - Diesel or petrol?

[Deker]

I think the modern engines are about the same in terms of reliability, diesel used to be more reliable due to being less complex and less reliant on ancillary components, now both engines are so reliant on sensors to work correctly they both probably now have a very similar failure rate and more than likely it's an sensor\cpu one rather than a mechanical one.

 

[Vlad]

I used to automatically think diesel, but in the last 10 years or so, my thoughts have changed....modern diesels have a tough job of meeting emissions and are therefore loaded with lots of emission related equipment, which seems to be effecting long term running costs compared to petrols, especially if you are doing low mileage, and mainly town related driving.

Clogged up EGR valves seem to be common and ive seen cars as low as 45,000 miles needing a new EGR valve. The latest soot traps seem to be causing all manner of problems, especially with low mileage, short journey interval cars, ie if they get clogged the cost can be huge, especially if the Cats have become damaged....again, have seen this on low mileage Mums cars which just trundle to school and back.

Injectors....in general diesel injectors seem to require earlier replacement than petrols

Turbos....seen a lot of turbo's on diesels needing replacement.

If you do a lot of high mileage + long duration driving then diesel reliabilty is not too bad but if its low mileage, short duration driving then petrol is the more reliable

Talking to the Techs at my local Mercedes Specialists...diesel cars provide plenty of work for them, whereas the petrols seems to go from one service to the next with very few issues.

 

[finisterre]

normally aspirated and carb free gives you an old diesel.
adding in petrol fuel injection makes it a tie.
adding a turbo and three part clutch, petrol wins.

possibly

 

[Bobby Dazzler]

Less to go wrong with a normally aspirated modern petrol engine, than a modern turbo diesel.

 

[The _Don]

Petrol.

 

[bluerainbow]

Tried diesel before didn't like it. Petrol piece of mind in the long run.

 

[Cabe]

Another question.

Does the fuel saving over a an engines lifetime pay for the potential repairs to a Diesel?

 

[BQF]

Diesel cars suffer fewer engine failures, are stronger (for the compression ratio - which is why if you want to NOx a car a diesel makes more sense), and have far fewer electrical items.

The only breakdowns I have suffered (apart from my front springs on the E-Class!) have been electrical or gasket failures - which are only really problems that plague petrols.

No-one really breaks down because the glow plugs on their diesels have failed ......

 

[blue gnome123]

There are some different questions here. Overall lifetime of a car engine (how long it lasts) and reliabilty in use over a period of time. A diesel will undoubtely last longer as an engine (so lifetime reliability) but a normally asiprated engine these days will probably have less go wrong in it's shorter lifetime, until it nears the end of it's life.

However many cars these days get scrapped wilst their enines are still working fine.

I think that mechanical normally aspirated diesels will last the longest. Not the best to drive though.

 

[Will]

Diesel cars suffer fewer engine failures, are stronger (for the compression ratio - which is why if you want to NOx a car a diesel makes more sense), and have far fewer electrical items.

The only breakdowns I have suffered (apart from my front springs on the E-Class!) have been electrical or gasket failures - which are only really problems that plague petrols.

No-one really breaks down because the glow plugs on their diesels have failed ......

But that's the point, modern diesels are more complex than regular petrol engines, and have more potential for expensive failure during their lifetime.

Almost all modern petrol and diesel engines will outlast the lifespan of the car that they are fitted to, you just don't hear of crank regrinds, rebores etc. It's stuff like broken diesel injectors, turbos and electronics that cost several hundreds of £££s to fix.

The biggest threat to the modern MB car is complex, costly electronics (not just engine-specific) and rust, mechanical engine wear is rarity.

Will

 

[grober]

Can I introduce a couple of wild cards into the mix ?

DIESEL PARTICULATE FILTERS!

and
Small capacity / high output / direct injection/turbocharged [ and sometimes supercharged as well ] petrol engines.

and while I'm at it

Bye Bye
Nice old torque converter coupled hydraulic automatic box

and HELLO
semi automatic twin clutch [ wet or dry sir?]preselect twin shaftelectro hydraulic gismo controlled gearbox.

aaaaaaarrrrgggghhhhh!

 

[bpsorrel]

Yes, but not all diesels have DPFs. Also, taking care of the turbo (giving the engine/turbo a few seconds to cool down before turning off) and ensuring correct oil change intervals, should prevent premature turbo failure - - so, with that in mind, are diesels still less reliable?

 

[tagnut]

I always believed that diesels were more reliable but I'm no longer convinced on this. I do think that they tend to outlast petrols but suspect that the figures are skewed by lower resale values for high mileage petrol cars making these uneconomical to repair sooner.

There is also the conventional wisdom that diesel engines will run on and on forever which I suspect leads many to carry out expensive repairs they might not have done on a petrol car. I suspect that the truth is that petrol cars will cost less in repairs over their lifetime but that this lifetime will be shorter due to residual prices. I also believe that the breaking of many cars is down to factors other than major engine problems.

I'd love to see some real data on long term maintenance costs of both types and how far the increased fuel consumption costs of petrol units would be off-set by the (I suspect) lower costs of maintenance. I've only had diesels for the last 9 years and this choice has been driven by the difference in fuel consumption and depreciation. I'm starting to think that, with some careful choices, I could have had cheaper motoring overall during this period if I'd stuck with petrol

 

[Will]

Not MB, but just today I was in at VW picking up a Passat 2.0 TDI that broke down last week.

Faulty fuel injector. Part alone £5/600 + 3.5 hours labour. Thankfully I wasn't footing the bill for that, and VW apparantlly offered some 'goodwill' as it's a common fault.

Car is 4 years old, just over 40k miles.

The service advisor chap reckons it'll be back again soon as when one go, the others follow soon after. Apparantly another customer's TDI that was in earlier for the same fault had an eventual bill of circa £2000 as it was more cost effiicient to replace the lot in one go - as it had broken down twice in 10 days, such is the reliability of these injectors - rather than paying 3.5 hours labour each time, plus other consumables.

As routine servicing was outside of the VW network there was no goodwill on offer either.

Ouch!

 

[jonnyboy]

Jesus christ.
And we've got a v8 diesel audi coming out of warranty next month......

 

[trapperjohn]

Extend that warranty if you can John.

Psst. Wanna buy a cracking 124 Diesel Estate in Red

 

[wemorgan]

*thread drift

does anyone know if the VAG 1.9 TDi engines are more reliable than the newer 2.0 TDI engines?

 

[Will]

*thread drift

does anyone know if the VAG 1.9 TDi engines are more reliable than the newer 2.0 TDI engines?

Apparantly they are in this respect (injectors) as the newer 2.0 TDI engine has different injectors (chocolate ones? ) to the older engine design.

I've known quite a few others with the older VAG 1.9 TDI PD engines who had no problems with injectors.

But - on a positive note, the particular car that I was referring to today with the injector fault has not had a single other breakdown in the last 4 years - not even a puncture, bulb or battery.

PS - a quick google (VW Passat Injector) and found this post on a thread on another motoring forum:

VW Passat 2.0 TDI Sport - VW Passat 06 Injector Fault, no joy with VW, help! | Motoring discussion | Back Room Forum | Honest John

Will

 

[BTB 500]

*thread drift

does anyone know if the VAG 1.9 TDi engines are more reliable than the newer 2.0 TDI engines?

Our 1.9 TDi (110 bhp) is coming up to 140k miles now and ... touch wood ... the only 'repair' it's needed was to replace a leaking oil pressure switch. It went through a phase of using oil, but doesn't seem to any more

 

[Will]

It went through a phase of using oil, the only 'repair' it's needed was to replace a leaking oil pressure switch, but doesn't seem to any more

Fixed that for you

Even the modern 2.0 TDIs seem to use about 1L every 3/4k miles or so, appears to be normal - with VW longlife oil I bet it works out to a few £s over the lifetime, must be worth a MPG at least