Diesel engines easily run 400.000km especially Mercedes cars but petrol will give up way sooner
In: Engineering
I regularly get 300,000 miles 483,000 km on my GM 3800 petrol cars. As a regular member of pretty much all top 10 best engine lists this is to be expected. I don’t know that there’s any currently selling engine that can go this far.
There are more moving parts, some of which have very critical timing and alignment. That raises the cost at a constant level of durability. However, people like inexpensive cars. The “solution” is to make less expensive parts, even if they are less durable, as few cars survive to reach 200,000km, much less 400.
This is a pretty common type of engineering tradeoff, cost vs durability.
Diesel fuel is lubricating. Petrol is a solvent. This also affects materials chosen for durability.
Biggest reason , moving parts . Diesel engines are lower revs then petrol , lower revs , less wear . The difference nowadays is near 0 , since the diesel engines have been pushed towards higher power outputs , vs petrol with low rpm turbos . It however still is the case for large engines , like in trucks , boats , where diesel is still running low rpm , they can run many many hours without breaking down .
I believe part of it is you need fewer revs to get the same power out of a diesel engine. So over several years that could be tens of millions of fewer revs on the diesel.
One big factor is RPM. Less cycling of the motor while traveling the same distance means that a diesel effectively sees less wear.
I’m not an expert on diesels but don’t they not even have an ignition system? The glow plugs need to be warmed up initially but then the combustion is caused mainly by the compression in the cylinder.
Diesel engines being built “stronger” means the parts in the engine that move around a lot, weigh more. This limits RPM which is less of an issue with diesel engines because diesel fuel generates more power per unit of fuel than gas. So diesels can rev lower and still make plenty of power. The higher reciprocating mass also generates more torque (the actual, measureable work) at lower RPM.
Not all diesel engines are robust. I had a 1995 GMC 3500 work truck with a diesel engine. In 4 years and less than 75K miles, it blew a head gasket and the engine was trash.
It’s not as easy as saying “diesel engines are more reliable than gasoline engines”.
There are plenty of ultra reliable gasoline engines that will run virtually forever with nothing more than basic maintenance. Just like there are plenty of diesel engines that are absolute garbage for reliability.
I think some of the bias in favor of diesel is that it tends to be the fuel of choice for heavy duty applications where long term reliability is more important than other applications where an engine is used. For example big trucks for transporting goods tend to accumulate a lot more miles than a personal car so the engines are designed to be more robust, which also makes them more expensive upfront. That upfront cost is worth it for the application but it’s not in a personal vehicle.
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