Diesel Engine Fuel Dilution
Diesel Engine Fuel Dilution
(OP)
I have been told by the OEM's that fuel dilution in the oil to within certain specified limits is acceptable. Any comments as to what you believe these acceptable limits should be and what the possible consequences of excessive fuel dilution could be.
Ken
Ken





RE: Diesel Engine Fuel Dilution
Oil dilution happens whenever fuel actually hits the cylinder walls before combusting, so it's a major concern with diesel misfire or things like post injection.
I've seen some test cell work in a research lab using post injection for some things on an engine that had a cylinder that would misfire when cold. After 100 hours of testing, they'd gotten about 9% oil dilution which I think translates into about a 25% loss of lubricity. The only thing that kept the engine from being severely damaged was the testing had only run at low speed/loads up to that point.
RE: Diesel Engine Fuel Dilution
RE: Diesel Engine Fuel Dilution
As to the cause of dilution, my experience has been with faulty injectors or fuel lines under the valve covers rather than misfires. Some engines (such as Cat 3406) have no return line from the injectors. Any fuel leakage from worn injectors goes into the oil. There are many other ways fuel can leak into the engine oil that are more likely than misfires.
RE: Diesel Engine Fuel Dilution
It also depends on viscosity of oil, bearing loads, clearances etc.
I have a question, how come diesel has enough lubricating qualities for the injection equipment, but supposedly not enough for the rest of the engine?
Isn't lubrication a fascinating subject?
RE: Diesel Engine Fuel Dilution
Cheers
Greg Locock
RE: Diesel Engine Fuel Dilution
Also, the loads bearing surfaces in the engine are much larger than the loads in the fuel pump.
Regards
pat pprimmer@acay.com.au
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RE: Diesel Engine Fuel Dilution
(He kept trying to tell me that it was a gasoline car, and that the fuel filler was up front, not in the rear.)
I ran it (not too hard) for several miles, whereupon I then dropped the oil, which would now flow freely, put fresh oil in, and ran that engine for many, many years thereafter.
That did not seem nearly as bad to me, with respect to dilution of the lubricating oil, as the time I got stuck in the creek, engine partially submerged, and I failed to remember that the crank shaft oil seal on a VW is a internally threading screw labrynth type seal, which promptly 'screwed' my engine full of water as it sat in the creek idling.
So much for dilution of the lubricating oil.
rmw
RE: Diesel Engine Fuel Dilution
As for the VW with oil dilution, it becomes a much bigger problem if your customers are are going 35,000 miles between oil drains and are hauling 80,000 lbs. of stuff up and down the interstate daily. Like I said, our prefered spec is 0%.
RE: Diesel Engine Fuel Dilution
On the subject of oil dilution; Consider the two stroke boat engines. They use 50 to one dilution. Forty years ago McCullough brought our a series of engines that used 100 to one. They were great performers and did not have crank problems. The rod bearings were needle bearings however.
I like to run jet boats. It is an all too common occurrence to fill the engine with water. This is due to the cooling water being supplied by the main jet pump. The operator gets the valving screwed up which pressurizes the water jacket to 100 psi or so. This blows through the gaskets of the old large blocks and fills the crankcase with water. The engine usually survives but it is a real mess to clean up.
RE: Diesel Engine Fuel Dilution
The reason diesel is ok for FIE and not for engines is, as stated above, the loading. In nearly all diesel FIE the lubrication of the high pressure parts is done by the fuel, and all the motion is effectively sliding. The lower parts with high contact forces or rubbing tend to have an oil feed or oil bath of normal lub oil.
I cant go into the specifics of what leaks where, as different applications have different needs.
RE: Diesel Engine Fuel Dilution
Neil