Why is the inside of a diesel engine cleaner than a gas engine?

Joined
Jun 11, 2013
Messages
33
Location
oxfordshire United KIngdom
I’ve recently been changing some timing chains on a mix of diesel and gas cars. I’ve noticed with the diesels, while the oil is generally black compared to the gas however the inside of the engines are cleaner, nothing has that golden tarnish or sludge that you see in gas engines? I’ve noticed the pistons and heads don’t have any heavy deposits on them, they’re black but it seems more like a thin layer of soot vs the heavy deposits seen on a gas car.

Why is this, is there something in gas that reacts with oil, do gas engines run hotter and burns the oil?
 
Gas burns hotter and perhaps they're tuned to run hotter as well. Oil should make no difference as they are dual rated for light duty passenger cars.
 
lower fractions of diesel are similar to kerosene/white spirit, generic cleaners.
and diesel fuel is also sometimes used for cleaning.
since boiling temp is so high, it may stay longer on surface doing his thing.
or maybe just prohibits oxygen to reach the oil.
 
diesel oil is designed to attract and suspend particulate and for two identical cars the diesel model will be burning less fuel for the same distance.
 
High speed diesel engines use HDEO engine oil . Diesel oil is what runs the engine.
 
Diesels make mostly soot? Fewer partially burned hydrocarbons leading to a narrower range of soluables? ive noticed this too and it’s a good question.
 
lower fractions of diesel are similar to kerosene/white spirit, generic cleaners.
and diesel fuel is also sometimes used for cleaning.
since boiling temp is so high, it may stay longer on surface doing his thing.
or maybe just prohibits oxygen to reach the oil.
I’m not sure how true any of this is but when I was an engine rebuilder, the previous owner got tired of adding motor oil because the 1ZZ-FE was burning oil at such a high rate, he started using Diesel Fuel, literally….

Let’s just says that engine cleaned up really nicely really fast, weirdly enough the VVT-i gears on that car get sticky and stop engagaing properly(no noise just don’t work properly) it was one of the handful of the VVT-i gears that actually worked properly out of the 99 1ZZ-FEs that I rebuilt. I think diesel fuel cleaned up that engine real nice, there wasn’t any scoring or damage on the engine though.
 
Gasoline is a nasty fuel, which, once partially burned, breaks down in oil to create sludge and varnish.
The hard sludge and varnish seems to be more prevalent in engines with egr.
Gasoline engines, even carburated ones in boats (which are often run hard with high oil temps and fuel residues in oil) are usually free of the particular hard tarry varnish and deposits found in modern emissions controlled gasoline engines.
 
Since everyone else is guessing…

I’ll go with lean burn. Lots of air and heat. No fuel present during compression stroke (no raw fuel slipping past rings) (well at least while running, starting would be different). But lots of air, so it burns fully or not at all.
 
Back
Top