Quote:
Originally Posted by Father Of Giants
Do gasoline engines suffer from fuel dilution more or do non gear heads akathe general public idle a lot?
I ask this because more often than not when I changed motor oil it reeks of gasoline, however my E320's dipstick does not have this smell.
I don't idle over 1 min unless at drive through.
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Bear with me for a moment - not necessarily a simple answer.
From my understanding and research the OM61x engines' oil change interval is dictated primarily by soot loading. The nature of their IDI design means they're less efficient than a DI diesel (like a VW TDI, Cummins 6BT, or modern Duramax, Powerstroke, etc.) and that begats more combustion contaminants in the oil. When soot saturation reaches a certain level it will result in accelerated wear, BUT that point on a 617 in any decent state of tune is far past what's seen under normal 3-5,000 mile intervals. My concensus when I got my 300CD and wanted to insure the engine's longevity was that 5,000 miles on a synthetic oil was safe under any conditions and regardless of how poorly (aka, inefficient) the engine could be running. Synthetics withstand heat better, are "slicker" (lower friction) and they also capture and control afore-mentioned soot better than conventionals. Not to mention the 617 holds two gallons of it, which is a much higher oil-volume-to-displacement ratio than a lot of engines of its day that still have a reputation for great longevity.
I've not done a lot of comparing of diesel vs. gas fuel dilution levels, but I *think* your average gas engine will have less fuel or fuel by-products in the oil than your average diesel. However! This doesn't apply to direct-injection gas engines, which started getting popular about 10 years ago and now are basically the norm. Instead of injecting the fuel into the intake manifold or head port, to be sucked in when the intake valve opens, they moved the injector into the combustion chamber - like a diesel engine. This allows higher compression ratios, where gas present in the combustion chamber on the compression stroke would pre-ignite, but when sprayed at the point ignition is needed followed by the firing of a spark plug it burns normally. Basically borrowing diesel designs to make gassers more efficient. Anyway, DI gas engines commonly dilute the oil worse than port-injected engines, sometimes to a point that can compromise the oil's ability to lubricate not far outside the recommended change interval. DI has had plenty of teething problems - troublesome injectors, high pressure fuel pumps (HPFP), carbon buildup on intake valves (because there's no gas passing by the intake valves to keep gunk washed off), etc.
That's not the whole scoop, but maybe it'll give you a better idea of the whole fuel dilution thing. BobistheOilGuy forum will have days worth of reading on this, if you care to search.