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Engine Life - Petrol vs Diesel

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Old 15 April 2010, 11:11 PM   #1
velohead66
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Default Engine Life - Petrol vs Diesel

Need to buy a vehicle asap, and have seen a Misubishi Pajero 3.0L V6 Petrol at a good price, but the milage is around 125,000 miles and is 1994.

Just wondering, for a well looked after engine (regular basic services, not pushed to extreme revs or adverse driving) then what is the life (in miles) for....
a) a non turbo fuel injected petrol engine
b) a non turbo diesel engine.

Also when the engine is starting to fail, what components start failing.

Thanks.
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Old 15 April 2010, 11:15 PM   #2
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Life is different for every engine. Some years some manufacturers make good engines, other times they don't. Also, there are not too many non turbo diesels around.

I'm guessing you are thinking about repair costs, but engines alone are not the only issue. Suspension, gearboxes etc also start having issues with lots of miles and can cost lots to solve.
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Old 15 April 2010, 11:15 PM   #3
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Damn SN and double posts

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Old 15 April 2010, 11:34 PM   #4
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Engines go on for 200,000 miles if looked after and not messed about with ..... regular Oil changes is the single thing which extends life - doesn't have to be expensive oil (just good oil)!
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Old 16 April 2010, 01:45 AM   #5
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A diesel should outlast a petrol by over double the mileage if serviced similary, the diesel will use half the revs to that of the petrol car (4 pot v 4 pot for instance) so less wear, but most as pete said will run 200k before needing a rebuild (though I have heard of diesels doing 1000k miles without being rebuilt, I have not heard of any petrol getting anywhere near that)

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Old 16 April 2010, 07:48 AM   #6
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the legendry 4.2 diesel engine in the Toyota Landcruiser will easily (and regularly) do 250 - 300 thousand miles
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Old 16 April 2010, 08:10 AM   #7
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Engines themselves last a long time but ancillaries ( pumps, turbos etc ) will go first.
So a difficult one to answer.
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Old 16 April 2010, 08:10 AM   #8
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X 2!

Last edited by thesyn; 16 April 2010 at 01:32 PM.
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Old 16 April 2010, 09:27 AM   #9
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Its usually neglect or rough treatment that kills engines, most cars go to the scrapper with perfectly good motors.
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Old 16 April 2010, 10:57 AM   #10
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My old Impreza Turbo was on 240K when I sold it and was still going strong. The only things replaced were water pump and radiator + a few oil seals.
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Old 16 April 2010, 11:07 AM   #11
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the car may be cheap - petrol cost and the pajero 3.0 petrol mileage work against it, you are looking around 20-25mpg real world driving.

Mitsi parts are not cheap, you could easily buy into a money pit that appears on the surface to be a good buy.
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Old 16 April 2010, 11:38 AM   #12
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I think you will struggle find a non-turbo diesel in ths day and age; but certainly these are the ones to plumb for.

Also one needs to consider the engine's output vs its capacity. And if its derated for commercial/industrial applications or uprated for performance/race use.

For example a 6.2litre 6 cylinder Perkins diesel producing 150BHP (as found in our old AWD truck) treated right would probably outlive its modern counterpart; an Iveco 3.9litre 4 cylinder with 160BHP (as found in its replacement).

Both engines have more or less the same output, but the Iveco is under alot more stress. Firstly it relys on high boost from the turbo to get its power. In comparison the Perkins is very understressed and has a very small low pressure turbo for scavenging purposes (mainly to reduce black smoke). Combine that the Iveco uses lighter weight materials for block, rods, crank and pistons whereas the Perkins is more over engineered, at a cost of increased weight.

The Perkins was still going strong when it was scrapped; the truck fell apart from around the engine and chassis. The gearbox had become very uncoperative, and the cab was ready to fall apart from rust.

I doubt the Iveco engine will last as long, be so durable or be so tolerant to faults or abuse (dribbling injectors or overboost etc) Rest of the truck may fare better as it has better corrosion protection. But then it has alot more elctronics on it and it is Italian (AWD had no electronics whatsoever ).


I could use the same argument for Subarus with the same capacity EJ20 engines: The old 200bhp Legacy 4cam Turbo vs a later (say MY99) 280bhp JDM Sti - which engine lasts the longest? Usually its the former. The latter is more stressed, and prone to abuse and modifications, and suffers as a result.

However, there are cases where engine design may dictate otherwise; For example, series II Landrover engines only had three main bearings on the crank. Both petrol and diesel versions used the same engine design (albeit the diesel had stronger components). The diesel, due to its high compression was notorious for crank flex, which in turn hammered the main bearings. The Petrol version had very low compression (so it can run on crap fuel) and inturn the crank and main bearings were less stressed and therefore the petrol engine tended to last longer.

Last edited by ALi-B; 16 April 2010 at 11:44 AM.
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Old 16 April 2010, 12:07 PM   #13
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Quote:
Originally Posted by ALi-B View Post
The diesel, due to its high compression was notorious for crank flex, which in turn hammered the main bearings. The Petrol version had very low compression (so it can run on crap fuel) and inturn the crank and main bearings were less stressed and therefore the petrol engine tended to last longer.
Presumably the flex is nothing to do with the compression ratio - it's the torque output that would cause it.

After all, any piston is pushed downwards with a lot more force than it took to push it upwards... that's where the power comes from!
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Old 16 April 2010, 12:11 PM   #14
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Diesels do tend to outlast petrol engines because of the lower revs but regular oil changes make an enormous difference as long as the correct oil for diesels has been used.

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Old 16 April 2010, 12:29 PM   #15
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Lower revs and stronger construction to withstand the higher compression but I wonder what the uber diesels will last like, the 335d for example, specific output is getting on for 100 bhp/litre.

Design and quality is a big factor, look at the K series, damn good little unit with a cruicial design flaw that sunk it, Honda did something similar, no design flaws and slightly heavier construction and it goes forever.

The gender of the owner has an impact as well
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Old 16 April 2010, 12:29 PM   #16
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Lower revs and stronger construction to withstand the higher compression but I wonder what the uber diesels will last like, the 335d for example, specific output is getting on for 100 bhp/litre.

Design and quality is a big factor, look at the K series, damn good little unit with a cruicial design flaw that sunk it, Honda did something similar, no design flaws and slightly heavier construction and it goes forever.

The gender of the owner has an impact as well
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Old 16 April 2010, 12:37 PM   #17
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Lower revs and stronger construction to withstand the higher compression but I wonder what the uber diesels will last like, the 335d for example, specific output is getting on for 100 bhp/litre.

Design and quality is a big factor, look at the K series, damn good little unit with a cruicial design flaw that sunk it, Honda did something similar, no design flaws and slightly heavier construction and it goes forever.

The gender of the owner has an impact as well
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Old 16 April 2010, 12:59 PM   #18
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Lower revs and stronger construction to withstand the higher compression but I wonder what the uber diesels will last like, the 335d for example, specific output is getting on for 100 bhp/litre.

Design and quality is a big factor, look at the K series, damn good little unit with a cruicial design flaw that sunk it, Honda did something similar, no design flaws and slightly heavier construction and it goes forever.

The gender of the owner has an impact as well
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Old 17 April 2010, 12:39 PM   #19
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That must be a posting record J4CKO.

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Old 17 April 2010, 01:43 PM   #20
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Holy triple post batman!
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Old 17 April 2010, 03:25 PM   #21
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My first car was a Peugeot 309, 1.9 Diesel, Bought it when i was 17 and it had 90,000 miles on the clock! The engine died at 256,000 miles. Put in another lump with 75,000. It had 400,000+ on the clock when i sold it on
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Old 17 April 2010, 03:31 PM   #22
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Quote:
Originally Posted by mr_impreza View Post
My first car was a Peugeot 309, 1.9 Diesel, Bought it when i was 17 and it had 90,000 miles on the clock! The engine died at 256,000 miles. Put in another lump with 75,000. It had 400,000+ on the clock when i sold it on
still thought you had a tractor for the sheep
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Old 18 April 2010, 09:35 AM   #23
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Thanks for the replies guys. Most informative.

Well, despite the wife saying NO upon hearing the milage of said vehicle, I managed to convince her to just see the vehicle, and meet the owner.
All your ponts helped.

The vehicle has a good service record, the seller seems sound to both of us and we have purchased said vehicle, as we needed one ASAP.
Pick vehicle up on Thursday, cant wait.

Thanks again.
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