Hi Folks
I remember many years back a friend telling me diesel engines ware normally good for double the amount of millage than a petrol engine - engines running at lower revs and diesel having a lubricant in the fuel were i seem to recall the main resons- . At that time before ecus he said around 100k-120 - pertrols and 200k for diesels. In recent posts on this forum it seems petrols engines are good for between 120-200k and i was wondering if diesel engines would still do double the amount of miles than a petrol - and if not why not??
Cheers
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The basic power unit (block, head etc) is good for very high miles. What tends to kill off a modern Diesel is some failure of the engine management system which costs more to repair than the car is worth - hence the car is scrapped.
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Ive seen a PSA HDI lump with 400K + miles on it, Think it was attached to a Citroen C5
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I doubt they can last longer. With large truck engine maybe it is worth stripping/re-building the engine and being fastidious with servicing. When a car gets old people start to neglect things. A cigarette burn on the upholstery probably has more effect on market value as you can see it; you cannot easily guess engine wear without leakdown/compression test.
Diesel engines use heavier parts but have more violent combusion process. Diesel engines do not rev as much which might suggest longer potential life. Petrol engines have problem that petrol works against the lubricant. Diesel engines have more dirty byproducts. If used on short trips diesel engines stay cold for longer which cannot be good.
The problem is always a lack of real data. If manufacturers have it they probably wouldn't advertise it, and there are many variables between bench testing and real life.
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Hi
Thanks for the reply just in realtion to the point quoted 'If used on short trips diesel engines stay cold for longer which cannot be good' why does a diesel engine take longer to warm up than a petrol engine on short trips???
Cheers
Andy
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Two reasons among many are;
1) Diesel engines are more thermally efficient - they reject proportionally less heat into the coolant or body of the engine
2) Diesel engines are heavier, hence they have higher thermal capacity - they need more thermal energy input (see point 1) per unit temperature rise
Number_Cruncher
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We've seen something of a revolution in recent years on the diesel front, not only in terms of technological advances, but also how diesels are marketed.
Go back even a decade, and diesels were mostly bought by economy minded motorists who weren't in the least bit interested in performance, and drove their cars accordingly. Typical service intervals were 6,000-9,000 miles, and the typical diesel engine even in turbo form made something around 50 bhp per litre. In short, most diesels were low-stressed, frequently serviced and driven gently.
Nowadays of course, we have the high specific output "performance diesel" which is marketed to enthusiast drivers, and is likely to be driven much harder. Plus of course, government tax policy has sent almost all fleets down the diesel route so the typical "boot to the floor" rep is likely to have an oil burner under control of his carpet-welded right foot, and fleet marketing has meant extended service intervals. I believe there are now diesel engines from Vauxhall and others that only require servicing every 30,000 miles according to manufacturer recommendation, and specific power outputs of 80 bhp + per litre are not uncommon.
I often wonder whether all this will result in the hitherto 250,000 mile diesel engine experiencing a much shorter life in many cases. The application for the diesel engine has changed beyond all recognition, the specific power outputs of modern diesels were undreamed of a decade ago, and service frequency is as little as a fifth in some cases.
This is only a hypothetical argument. I have no evidence that modern diesels are any better or worse in longevity terms than their ancestors, although I have heard of several with very expensive component failure at relatively small mileages. As was mentioned above.
Cheers
DP
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Thanks for thoughts on this issue. Thats interesting to hear of major componant failure at around 250k on a diesel. I would be interested to know what sort of components needed repacing at at this millage?
Cheers
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