Diesel in engine oil

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crown22

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Hi everybody a follow up thread. The contents of the sump are now in a clear container in my garage.About 2.4 litres pumped out maybe 0.2 litres that the pump
couldn't reach and maybe 0.2 litres that went into the bilge when I removed the dipstick. Yanmar 2GM20.Capacity is supposed to be two litres. So can't decide for
sure if it was overfilled by the previous owner before I bought it or there is diesel in the oil. I expected the diesel and oil to separate but that hasn't happened yet?
The viscosity seems thin to me compared to what comes out of my Mondeo diesel car engine? Or maybe 5/30 oil was used? So maybe there is no diesel in the engine oil
and I have been worrying without good reason and all that has happened is that the previous owner has overfilled with low viscosity oil? Thanks again.
 
My only experience of this was on an agricultural engine. There was a small split in a rubber gasket on the fuel pump. The fuel pump is operated by a cam within the engine oily side. Might be worth removing the pump just to check it.
It was an easy fix with a replacement fuelpump.
 
Don't think the oil and diesel will seperate, but it should smell a bit of diesel?
The faulty fuel pulp diaphragm has been talked about before in these cases, well worth a look. Parts4engines do a well priced one.

About the previous owner over filling. I thought you checked the level sometime before it overflowed?
 
If you have diesel in the oil to any material extent you will smell it.If you do have diesel in the oil most likely cause is the fuel pump diaphragm as has been mentioned. If its not the fuel pump could be fuel wash down the cylinder if the timing is slightly out-basically if the injectors are realising fuel too early or late it may not all burn and can get past the rings and drop in to the sump. The crack you experienced may indicate some timing issue. May be worth checking if it is not a leaking fuel pump-I have experienced it once myself on a 3GM and took a lot of tracking down.
 
Not really sure how diesel would get into your oil.
I would think best way to find out is to check density.
Or send a sample to be tested.
Might as well find out for sure.
 
If it doesn't clearly smell of diesel and it doesn't look like water mixed my guess is its an over fill of oil. Thinking about the oil coming up the pipe it could be just from being overfilled when running. Oil should live in the sump other than when its being pumped around the engine. If its too high and enough that the crank is running in a bath of oil it will froth up which I'd imagine could be enough for it to push some up the tube when its hot. Could be good news. But remind us what happened with the crack sound. Did the engine miss a beat or was it just a sound you heard while it was running?
 
The test we used to use to check the ship's diesel generators for oil dilution involved two small cups, about the size of egg cups, which each had a small hole in the bottom. These were hung from a small frame with a receptacle beneath. Into these were poured some of the sample plus a quantity of new oil, the time they took to rain through was then compared, and if the used oil was noticeably faster then this would denote the oil was excessively diluted and hence of lower viscosity. At a certain dilution a change was required.

I recall this is also how an oil's viscosity in Redwood Seconds is established, but lube oil viscosities are normally measured in centistokes.

There is plenty to read about fuel dilution if you google it. Most oil labs would use gas chromatography to determine dilution levels. A typical Finnings test is about £25, and will tell you a lot more than just the viscosity.
 
superheat6k said:
The test we used to use to check the ship's diesel generators for oil dilution involved two small cups, about the size of egg cups, which each had a small hole in the bottom. These were hung from a small frame with a receptacle beneath. Into these were poured some of the sample plus a quantity of new oil, the time they took to rain through was then compared, and if the used oil was noticeably faster then this would denote the oil was excessively diluted and hence of lower viscosity. At a certain dilution a change was required.

I recall this is also how an oil's viscosity in Redwood Seconds is established, but lube oil viscosities are normally measured in centistokes.

There is plenty to read about fuel dilution if you google it. Most oil labs would use gas chromatography to determine dilution levels. A typical Finnings test is about £25, and will tell you a lot more than just the viscosity.
Click to expand...
I have done hundreds of these tests, using the brass cup with a calibrated hole in the bottom, on bitumen cutback solutions. Used to take longer to clean the cup afterwards than to do the test!
 
The usual cause of large amounts of fuel dilution is from a leaky diaphragm on the lift pump however most small diesels with fuel pumps in the crankcase such as Volvo 2000 , 2020 MD 2 MD 2b Beta Nanni Yanmar 2gm etc do have minute constant spill leakage into the crankcase hence the reason for frequent oil changes.

If there is as much diesel as you suggest then you should smell it on the dipstick and it the oil must be removed as oil with this amount of diesel contamination may cause an engine runaway especially of there are worn piston rings.
 
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How do you know the capacity of your sump? I ask because that written on the instruction manual for my gearbox was woefully out: I duly put a container below it of a bit more than the manual said, and opened the drain. Panic a few mins later as said container overflowed into the bilge... The manual was just a work of fiction.

Perhaps not surprising as most manuals were written 30 years ago by those B-ark people whom R&D had already rejected as numpties not to be trusted with a actual design, and have never been rewritten since (or updated despite design changes, diesel moving to ULSD, or synthetic oils becoming cheaper than mineral etc, etc... ).
 
crown22 said:
Hi everybody a follow up thread. The contents of the sump are now in a clear container in my garage.About 2.4 litres pumped out maybe 0.2 litres that the pump
couldn't reach and maybe 0.2 litres that went into the bilge when I removed the dipstick. Yanmar 2GM20.Capacity is supposed to be two litres. So can't decide for
sure if it was overfilled by the previous owner before I bought it or there is diesel in the oil. I expected the diesel and oil to separate but that hasn't happened yet?
The viscosity seems thin to me compared to what comes out of my Mondeo diesel car engine? Or maybe 5/30 oil was used? So maybe there is no diesel in the engine oil
and I have been worrying without good reason and all that has happened is that the previous owner has overfilled with low viscosity oil? Thanks again.
Click to expand...
Not quite the same engine, mine is the 3GM30F. The sump capacity according to the manual is 2.6 litres. I know that an oil change for engine and gearbox using my Pela, not changing the filter, takes exactly 2 litres.
 
Hi everybody I compared the smell of my Ford Mondeo Diesel dipstick with what came out of the Yanmar sump. Fairly certain that the Yanmar oil smells of diesel. It hasn't separated in the sample jar I saved. So maybe I checked the oil level correctly before my short
90 mins of motoring?Thanks DownWest. My main suspect now is the lift pump diaphragm.Does anybody know if it would leak diesel into the sump even when the engine is not running?The fuel stopcock next to the tank is seized open. Another winter lift out job.! I might try making a clamp to squeeze shut the rubber pipe connecting the first stage fuel filter to the lift pump.
 
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