Why do diesel engines last longer ? - Dan G
I have often wondered why diesel engines last longer than petrol engines, although have never reached a conclusion. Here are a few reasons I have though of, but would welcome a more educated opinion.

Lower power output (will the new generation high output engines not last quite as long ?)
Heavier construction
Lower combustion temperature
Lower reving
Burns oil (a lubricant)

anything else ?
Why do diesel engines last longer ? - Cardew
There are numerous sites on the net discussing this subject, and you have given the main reasons.
To withstand the higher compression ratios a diesel has to be built more ruggedly and it uses less revs.
Why do diesel engines last longer ? - J Bonington Jagworth
I remember LJK Setright posing this question in order to answer it - he said that if petrol engines were made as robustly as diesels have to be, they would last just as long. A lot depends on the duty cycle, of course - big diesels in lorries are mostly on long trips (or at least kept running) and are well maintained. Car owners often lose interest after the newness has worn off...
Why do diesel engines last longer ? - Dan G
But lorry engines rev very slowly and produce relatively little power for their size, so they're built to last.

So a modern 1.9 diesel engine producing 150bhp will not last as long as a tradional 60bhp one ?
Why do diesel engines last longer ? - Cardew
Many diesel engines in cars are 'beefed up' versions of the manufacturer's petrol engine. In that case I suspect it is engineering common sense that lower output = lower stress = longer life.

However for both diesel and petrol it is the peripheral items on an engine - water pump, injection pump etc - that usually cause problems rather than pistons crankshaft etc; and even a petrol engine usually outlasts the rest of the car.

I recall an Olympic athlete suffering from terminal cancer commenting wryly that the doctors had assured him that his cardio-vascular system was good for another hundred years!
Why do diesel engines last longer ? - Nortones2
Dan: it is often said that diesels last "longer", but the nub is, which components of the "shorter lived" petrol engine cause it to eventually fail, and why? Does a diesel fail in the same way, but at a greater number of miles?

I suspect they both go to the knackers yard with the same ailments: piston rings and valves fail first, causing blow-by at both ends, as it were. Rather like humans really. If these are the culprits, it points to higher engine revs in petrol engines as one factor, (greater maximum piston speed) with lubrication failings also prominent, as your list picks up. As for the valves, combustion temperature? Robustness of build seems to have little to do with it, if my suggestion has any merit, unless rings are bigger and better in some way on a diesel. LJK might well provide some facts, rather than my loose speculation, but failing his august input, perhaps someone else would step into the breach with a few facts.
Why do diesel engines last longer ? - Peter D
They do not rev above 4000 rpm so they last longer. Simple. Regards Peter
Why do diesel engines last longer ? - tunacat
I know they're not diesel, but does that almost guarantee no-one's likely to get 200k miles out of a Honda V-TEC?

Any high-mile S2000s out there..?
Why do diesel engines last longer ? - flatfour
Don't believe it, my experience with Ford Mondeo diesel engines in my company fleet is that they bite the dust after 150K the petrol engines are good for 200k, its just a myth look at land rover diesels lots of work required, new injectors etc at 40k, they are generally serviced more often.

Enjoy life buy a petrol, no mess at the filling staion, no stinky slipperry shoes, nice smooth acceleration, no flat spots, no black fumes to give other drivers cancer, and listen, i can't here the engine ticking over, the diesel driver is being shaken to bits, ooops he's a hundred yards behind. he he he!
Why do diesel engines last longer ? - AlanGowdy
Indeed Flatfour - but 30 mpg? No thanks.
Why do diesel engines last longer ? - none
I think Newton might be right. (equal and opposite reactions).
For every horsepower (?) produced at the flywheel another horsepower has to be dissipated within the engine. Big heavy engines can cope. Small engines can't
Why do diesel engines last longer ? - jeds
The petrol engine just gets loaded more often than the diesel. Take the example of the motorway - cruise at 70-75mph and you need to overtake. The diesel (with turbo) accelerates gently with plenty of power and you can safely merge into faster lanes with plenty to spare. Equivalent petrol engines are capable of the same but, unless you can plan ahead and start accelerating before you pull out, you have to thrash them a lot harder to achieve it. And petrol is about a squillion times more poisonous than diesel.
Why do diesel engines last longer ? - GIM
It doesn't have to be knackered after 150,000 to 200,000 miles.

One Million Miles On Mobil 1
As one example of the level of testing undertaken, a 1990 model year import car was tested for 1,000,000 miles with Advanced Formula Mobil 1 and showed extremely low wear. Oil drain intervals were 7,500 miles, as specified by the manufacturer, and Mobil 1 was used from the very first day of testing.

After the end of the test, with 1,001,120 miles on the vehicle, the engine was removed and internal components were inspected and measured. Overall engine wear was extremely light. In fact, with the exception of light to moderate wear on the camshaft and followers, no other significant engine wear was noted. Oil consumption over the entire test was just 0.040 quarts/1,000 miles ? the equivalent of just one quart every 25,000 miles

Why do diesel engines last longer ? - Cliff Pope
I'm not convinced that diesels do last longer. You have to compare like for like in each situation.
Bigger petrol-engined cars can do phenomenal mileages - look at 2million mile Voilvo man. Do diesels last so long?
Virtually all lorries are diesels, so of course they appear to last a long time. But petrol lorries used to be commonplace (taxed off the roads). Army lorries were all petrol, and those big Bedford RLs look as if they would go on for ever.
Why do diesel engines last longer ? - Cardew
Cliff,
"Army lorries were all petrol,"

But not for many years now - just about everything is diesel.

To be fair the logistics of storing & transporting fuel - particularly on operations - is an important factor in the choice of a common fuel for the 'Green Fleet' and generators etc.



C

Why do diesel engines last longer ? - Cliff Pope
Cliff,
"Army lorries were all petrol,"
But not for many years now - just about everything is
diesel.



I know, I meant back in WW2 days, and for a long time after.
In the late 60s I remember the standard army lorries were petrol. I have memories of riding with a corporal who thrashed one across army roads on Dartmoor, sliding it round corners like a sports car.
Why do diesel engines last longer ? - Baskerville
If you look back at The Times newspaper from the 1930s you'll find lots of articles about this newfangled thing called the diesel engine and lots of discussion about whether they were be as reliable and economical to run in a truck as petrol. Ha! I reckon we're in a similar situation (in this country) with cars, with loads of people scared of this thing they don't understand but have heard lots of rumours about. How big would a petrol engine have to be and how many cylinders would it need to have to pull 40 tonnes at 70mph? Most trucks these days are more than capable of that.
Why do diesel engines last longer ? - J Bonington Jagworth
"How big would a petrol engine have to be and how many cylinders would it need to have to pull 40 tonnes at 70mph?"

The short answer is not as big as the diesel! Petrol engines were used extensively for trucks and buses in the US until it became expensive ($1/gallon, hah!). Not too many diesel aeroplanes yet, I'm glad to say...
Why do diesel engines last longer ? - PhilW
"Not too many diesel aeroplanes yet, I'm glad to say... "

And how many petrol engined ones? Well at least those comparable with 40 tonne trucks rather than those comparable with cars that carry 4 passengers not a couple of hundred?
Why do diesel engines last longer ? - Hugo {P}
"Not too many diesel aeroplanes yet, I'm glad to say... "


Well, the chances of one runnig at say 5000 ft with sub zero temperatures - not high I'm sure!

My sister and BiL had a Discovery in Khasakstan. Only they had to go for the V8 Petrol. I say "Had to", they didn't want the diesel to freeze!


Hugo

"Forever indebted to experience of others"
Why do diesel engines last longer ? - J Bonington Jagworth
Depends when you're talking about. Pre-jet area, practically all of them of course, but there still a few transport planes, mostly radial-engined. There were some magnificent engines, too, such as the 27-litre V12 Merlin and the Pratt & Whitney 18-cylinder Twin Wasp radial, both of which powered both fighters and bombers (sports cars and trucks, by analogy).

I was just trying to correct an apparent impression that only diesels were capable of serious amounts of grunt. A ride behind any big petrol V8 should help correct that, however (preferably a 427 Cobra)... :-)
Why do diesel engines last longer ? - J Bonington Jagworth
Ooh, and I should have mentioned the Napier Sabre H-24 (effectively two flat-12's on top of each other) which produced almost 4000hp from a mere 36 litres over 50 years ago. Mind you, that did have some methanol to help it along.

BTW, that would a wonderful fuel to use now (easily obtained from renewable resources) but of course politics prevents it.
Why do diesel engines last longer ? - Nortones2
JBJ; more than you yhink, but not v. friendly. WW2 Junkers 2-stroke diesels aircraft engines were quite numerous. Some work now going on for less belligerent, smaller scale applications. Not by Junkers though.
Why do diesel engines last longer ? - J Bonington Jagworth
Thanks, Nortones. I did know that there were some new small ones appearing, although I still think that for an application where smoothness and lightness are paramount, they are less than ideal. I worked next to a small factory that was prototyping one a few years ago, and it shook the place apart whenever they ran it (as well as making the most appalling racket!)
Why do diesel engines last longer ? - Baskerville
Hi JBJ

Have you any idea what the fuel consumption was like for the same power? Pretty bad I suspect to trigger such a radical shift. It strikes me that in general petrol engines that produce a lot of power (such as in F1 cars) tend to have a lot of small cylinders (around 300 to 500cc per cylinder seems to be optimal) whereas diesel engines that produce a lot of power (power stations, ships) have a few huge cylinders. So I guess the current Ferrari V10 is powerful enough to pull a 40 tonne truck at 70mph, but 17,000 rpm is hardly fuel efficient or convenient.

Chris
Why do diesel engines last longer ? - jon_s
One advantage diesel engines have is their scalability to cope with different applications. This is well illustrated by the huge two-stroke, direct-drive diesel engines used in large merchant ships.

To give you some idea of the statistics:

MAN B&W 14K98MC 2-stroke marine diesel engine
Bore: 980mm
Stroke: 2660mm
No. of cylinders: 14

If you work out the cubic capacity of this engine it comes to..... over 28,000 litres!!

And the power output? Wait for it..... 108,920 bhp!!!! And all at 94rpm!

OK, getting away from the topic of the original post somewhat, but it illustrates the versatility of the diesel engine.

Rgds,

Jon
Why do diesel engines last longer ? - J Bonington Jagworth
Jon - While I was composing mine... Makes the Sulzer look quite speedy! :-)
Why do diesel engines last longer ? - J Bonington Jagworth
"108,920 bhp!"

Of course, that's only 4hp/litre... (but they are nearly 50% efficient, which is why they are used)
Why do diesel engines last longer ? - J Bonington Jagworth
Well, specific fuel consumption will always be worse for a petrol engine, as even I have to admit that they are less efficient. The point I was trying to make was that petrol engines can do the same job - it's just that the ones we usually see are smaller and designed for power at high revs rather than torque at lower speeds. With diesels, there's less choice, as they can't rev all that high (because of the way the fuel burns), and although they have a flat torque band, it's not very wide, which is why diesel lorries have to have lots of gears.

The bigger the individual cylinders (and the longer the stroke), the faster the piston has to go to complete a revolution, so small multi-cylinder engines can spin faster without tearing themselves apart, but if you just want lots of grunt (torque), a fewer big cylinders will suffice (and will be cheaper to build and maintain). An extreme example is the Sulzer 2-stroke diesel designed for ships, which has a 3-foot bore (you climb inside to de-coke it), an 8-foot stroke and produces maximum power at 100 rpm...

WRT the Ferrari F1 engine in a lorry, it would need a lot of gearing and a big clutch to get moving, I think!

To return to the original topic, the thing that affects engine wear the most is duty cycle. A small car driven on frequent short journeys is bound to wear out sooner than a long-haul truck. The same would still apply if the car was a diesel and the truck had a petrol engine.
Why do diesel engines last longer ? - Altea Ego
"So I guess the current Ferrari V10 is powerful enough to pull a 40 tonne truck at 70mph, but 17,000 rpm is hardly fuel efficient or convenient."

ONly if it was doing 70 mph at the time you hitched the truck up. A 900bhp 17k revs ferrari f1 would not be able to pull away if attached to a 40 ton truck

(anyway the rear wing would pull off where you attached the rope)
Why do diesel engines last longer ? - Vagelis
"And petrol is about a squillion times more poisonous than diesel."

Not so, jeds. Petrol is a product of a higher distillation process than diesel. You could even drink (a small quantity of) petrol and not harm yourself. Diesel? Don't think so...

Vagelis.
Why do diesel engines last longer ? - Nortones2
I'd advise strongly against drinking petrol in any quantity! Petrol is classified as 'Harmful by ingestion': because of the aspiration hazard i.e. the risk of chemical pneumonitis, and not because of its acute toxicity i.e. poisoning, properties, which is a case by case variable depending on additives, sulphur and lead content remnants.    The presence of up to 5% benzene also means that petrol is classified as Carcinogenic. Not to mention flammable poo, when the residues leave their temporary home. Usual disclaimers as I am not currently au fait with COSHH etc.
Why do diesel engines last longer ? - Altea Ego
Nortones, with your permission allow me to clarify "chemical pneumonitis" in laymans terms as this happened to an uncle of mine after digesting petrol during a syphoning exercise. In short he died. Months later. Suffocated. Lungs like lace curtains according to the pathology report.
Why do diesel engines last longer ? - jeds
I know a farmer (well, I say farmer - more of a farmer one-cow really. But a great character) who has been taking the odd sip of diesel, when syphoning from one clapped out old machine to another, for about 40 years. He reckons it keeps his sinuses clear. Not that I am recommending it but, as mentioned above, you would not last long if you tried the same thing with petrol.

In any case, I was really referring to emissions - don't get me wrong, they're both pretty toxic but petrol emissions are microscopic and are much more easily absorbed into the blood stream. Ironically, people think diesel is more harmful because of the visible 'choking black smoke'. In fact the smoke is visible because the particles are massively bigger and, although it doesn't look pretty, this makes diesel emissions less easy to absorb.
Why do diesel engines last longer ? - Cliff Pope
Diesel engines may last longer, but their owners don't. Anyone remember the recent research showing how how taxi drivers are at increased cancer risk from inhaling diesel fumes all day?
Why do diesel engines last longer ? - Nortones2
Not necessarily diesel fumes. Most traffic in town is petrol engined, and the atmosphere in a taxi drivers cab, historically, has been full of nasties from smoking. Ordrs of magnitude more important, I'd guess. Defra summary:

"By contrast, a study of lung cancer in professional drivers in Sweden showed an increased risk among those working in the city of Stockholm (Jakobsseen et al., 1997), especially in short-distance lorry drivers; these findings allowed for the effects of smoking and the authors suggested that exposure to traffic fumes might have been responsible, although no data were available on atmospheric concentrations of PAHs within the cabs. A study in Denmark, which focused upon employed men who were diagnosed with lung cancer between 1970 and 1989, also revealed a 31 to 64% excess risk of lung cancer in bus, lorry and taxi drivers (Hansen et al., 1998). The smoking habits of Danish drivers and those in other types of employment were found to be similar. However, in the absence of exposure measurements, the contribution of PAH exposure to this result is unclear.

Summary

28. There is clear evidence that PAH mixtures are carcinogenic in humans and several individual PAHs are carcinogenic in experimental animals. Cancers result from exposure to PAHs over several decades. Increased risks of lung cancer, in particular, have been associated with increased concentrations of PAHs in the workplace. There is epidemiological evidence of an association between urban air pollution and excess risk of lung cancer in those most highly exposed, but risks cannot be estimated confidently from these data because of possible confounding by smoking and lack of information on historical exposure levels."
Why do diesel engines last longer ? - Nortones2
Thats fine RF, but an unfortunate end for your Uncle.
 

Value my car