Lifespan gasoline vs diesel engine

Joined
Jun 14, 2011
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Denmark, Europe
Hi,

I once read that the major reason why gasoline engines have a shorter lifespan than diesel engines is the cylinder wall wetting problem: Since diesel fuel acts as a lubricant itself, it will hardly have a negative effect on the cylinder wall wear.

Contrary, gasoline fuel dilutes the oil film on the cylinder walls, especially during startup when the engine is cold and more fuel is injected into the engine. This wetting of the wall with gasoline will cause increased wear in the cylinder wall. As a result, the engine will loose its compression over time and will need a complete overhaul.

This should explain why diesel engines have a longer lifespan than gasoline engines.

BUT. Is this still true? Is this "old news" from the times with carbureted engines where the choke nozzle injected large amounts of fuel into the cylinders and nowadays the electronic fuel injections with much better spray patterns dont show this problem at all?

What is your opinion on this topic? Do modern gasoline engines show significantly less wear than old carbureted engines?

Lucas
 
Joined
Aug 20, 2003
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18,958
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NE,Ohio
Diesel run at lower rpm lower rpm = less wear?
modern DI engines have the worst fuel dilution in ages much worse than port injection.

there are too many changes with modern tooling and engine metallurgy(among other things) vs how they were made 50 years ago. its Impossible to draw direct conclusions.. with "cylinder wall wetting"
 
Joined
Nov 24, 2003
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3,408
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Middle of Iowa
Things to think about...

Yes, diesels run at lower speeds, but they also usually have longer strokes, that means the RPM's might be lower, but average piston speed may be similar to a higher revving SI engine.

Diesel engines also take in a "full breath" every intake stroke, so the average cylinder pressure is much higher (higher compression, and compressing a full air load every stroke), so stress on rings/bearings/etc. will be on average higher

IMHO, there may be a small contributing factor to the fuel lubricity, but mostly the longevity is a product of designing an engine that is expected to have a higher duty cycle, higher load life, and longer expected life. If the robustness of a diesel engine were used to build a SI engine, I would venture to guess it would live just as long. Look at the SI engines that have been used in industrial applications....
 
Joined
Mar 20, 2008
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14,330
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USA
100k used to be considered high mileage a long time ago, whereas now 200-300k is no problem at all.

There are too many variables here. Besides what everybody else mentioned, diesels are more likely to be used for long highway driving, which is easier on an engine than stop and go. They also have huge oil sumps (gallons rather than quarts)
 
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Feb 27, 2009
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down in the park
Modern diesels, being direct injection, inject the fuel into a cup in the piston. Cylinder wetting doesn't happen unless you have an injection event when the piston isn't near TDC (pilot injections, post injections or dpf regeneration injections). But they alo have much higher cylinder pressures, and more brutal ignition events. All the fuel burns at the same time basically, coparable to knocking in a gas engine.

And soot.

Older indirect injection diesels injected fuel into a pre chamber in the head, again no issues with wall wetting unless theres mechanical issues, or it's too cold when starting
 
Joined
Jun 4, 2005
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427
Location
Cow Hampshire
In consumer trucks and cars I believe diesels last longer because owners who purchased them are more willing to maintain or repair them.

Almost similar to people with higher mileage Toyota / Honda willing to repair or maintain them because they “last longer”.
 

CleanSump

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Dec 13, 2019
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Quite a few generalizations here that aren't really correct. Maybe carried over from the olden days when few people had diesels except large trucks.
Having owned diesel powered European cars for over 35 years, I can testify they run at the same speeds as the gas motors in the same car/suv.
They don't use thicker oil. The manufacturers spec the same viscosities as their gasoline engines. Many, many owners of the pre-dpf ran a typical American 15W-40 or 10W-40, but the Euro manufacturers didn't require that. This was before 2000 and manufactures weren't requiring or recommending synthetic yet. Mobil 1 and Amsoil were about it for general use synth. And many argued the Mobil 1 "CD" then "CF" ratings weren't good enough in the '90s/early 2ks. (Myths included you'd burn oil, leak, wear out your engine, "it isn't designed for synthetic", and "real" oil is better balogna you still hear.) :eek:
Many of the Euro makes now spec the same oil for gas and diesel.
 
Joined
Nov 4, 2014
Messages
611
Location
Wichita Falls, TX
Quite a few generalizations here that aren't really correct. Maybe carried over from the olden days when few people had diesels except large trucks.
Having owned diesel powered European cars for over 35 years, I can testify they run at the same speeds as the gas motors in the same car/suv.
They don't use thicker oil. The manufacturers spec the same viscosities as their gasoline engines. Many, many owners of the pre-dpf ran a typical American 15W-40 or 10W-40, but the Euro manufacturers didn't require that. This was before 2000 and manufactures weren't requiring or recommending synthetic yet. Mobil 1 and Amsoil were about it for general use synth. And many argued the Mobil 1 "CD" then "CF" ratings weren't good enough in the '90s/early 2ks. (Myths included you'd burn oil, leak, wear out your engine, "it isn't designed for synthetic", and "real" oil is better balogna you still hear.) :eek:
Many of the Euro makes now spec the same oil for gas and diesel.
I agree about the generalizations presented by others. I had a 2007 Ram with the Cummins 6.7L diesel. At freeway speeds the engine was turning 1800-2200 RPM. I used 5W-40 or 0W-40 oil. Not too different from a gasoline engine.

Diesels don't always last longer. I had a lot of trouble with my Cummins, mostly due to the new emissions equipment that was mandated by the EPA. My turbo was replaced under warranty at 30K miles. I had to replace the head gasket twice before it hit 140K miles. Now I have a Ram 1500 with the Hemi gas engine, which turns slower at freeway speed than my Cummins did.
 
Joined
Jul 30, 2003
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2,347
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GA
In consumer trucks and cars I believe diesels last longer because owners who purchased them are more willing to maintain or repair them.

Almost similar to people with higher mileage Toyota / Honda willing to repair or maintain them because they “last longer”

Also, the target demographic for imports has been very different than domestics for decades. Two very different types of people in general with two very different driving, um, "habits".
 
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