contaminated oil

[candycat]

I have Yanmar 3GM30F and there seems to be fuel in the oil. We changed oil and put in new fuel lift pump but problem still exists upon looking at the oil again.
What else can I rule out
Thank you

[senormechanico]

I'm no diesel mechanic, but I'm familiar with the engine. I assume you changed the oil after finding diesel in the oil. Did you change the filter? There may possibly be a little diesel left over even if you did that.

Does it run ok?

Steve B.

[Boracay]

I don't know what the Yanmar uses as a lift pump but if it is the normal diaphragm type them the diaphragm can develop small leaks that allow diesel fuel inside the engine.

[Alan Wheeler]

How do you know there is fuel in the oil. It takes a lot of fuel before you can easily detect it.
Fuel can enter in a number of ways, but before I go there, lets see the answer to my question, and we can then dig in a little deeper.

[senormechanico]

Boracay,
I had a 3hm35 and it had a conventional diaphragm lift pump driven by an eccentric.
I am assuming the 3GM had the same.

Alan,
Is there a possibility that the injection pump could pee into the crankcase?

Steve B.

[Alan Wheeler]

Pat woudl be the better to ask on that. But I would say no. As I said, it's a lot of fuel required before you can be sure, from visual inspection that is. A proper oil sample is required for true confirmation. If the amount of fuel required is in there, you would notice a rise in oil level. Apart from the lift pump, fuel can get in via the cyclinder. but there would be many tell tale signs in the exhaust smoke to suggest a badly worn engine, or a failed injector.

[GordMay]

Raw Fuel in the Engine Crankcase Oil is called FUEL DILUTION, which lowers the oil's viscosity and flash point.

Every engine generates normal amounts of fuel dilution. Unburned fuel is normally evaporated from the heat of the engine.

Depending of the application and operating conditions, 0.1 to 1.5% (by volume) fuel dilution may be allowed, provided viscosity has not changed.
However, at anything over 1%, it may be recommended to examine the engine and analyze operating conditions.

Dilution ranging between 2.5% to 5.0% is considered excessive and requires immediate maintenance action.

If fuel dilution problems(*1) occur, it is necessary to correct the root causes(*2) of the contamination.

Oil analysis(*3) can provide an immediate answer to determine whether there is fuel dilution occurring in the engine.

1. PROBLEMS:
-Reduced oil viscosity
- Disrupts the oil film strength causing metal asperities to contact each other promoting engine wear, particularly in the cylinder/ring area.
- Increases volatility (in very extreme cases it can lead to a crankcase explosion)
- Weakened lubricant detergency
- Accelerated lubricant oxidation
- Varnish formation
- Acid formation/corrosion
- Low oil pressure

2. CAUSES: Excessive fuel dilution is caused by improper operation, such as extended idling, low compression, cold (short duration) engine operation, overloading, or by worn pistons (blow-by), and/or defects in the fuel or air delivery systems (Restricted: fuel return line, or air supply, or exhaust system).

3. ANALYSIS: Fuel dilution is detected in the laboratory by three (or more) methods: viscosity, flash point and gas chromatography.

[candycat]

In answer to the questions: Yes the oil filter was changed with the oil. We will be sending out the oil for analysis but the oil does smell like diesel and the viscosity is thinner. There was also a rise in oil level again. Initially there was black exhaust smoke but after the lift pump was changed it ran fine however when checking the oil again it looked thin and the level rose.
This engine has had a history of problems and we had new injectors put in last year. The engine had the 2 year European warranty but it was a constant fight to get things paid for under the warranty. Of course the warranty was up 4 months ago.

[GordMay]

Restricted: fuel return line, or air supply, or exhaust system?

[candycat]

We sent for the oil analysis kit so we can send it off ASAP. What a great forum this is; we are exploring everything. So much knowledge and it is most appreciated. Thank you

[David M]

Good..an oil analysis takes much of the guess work out of diagnosing the problem

[Joli]

Usually if you are making oil it is going to be a bad mechanical fuel pump seal. Any chance you can get a refit for an electonic pump?

Also check compression. Is the engine box dirty?

[never monday]

Is this a 3GM30F-YEU?
How many hours between the pump replacement and the latest observation?

[candycat]

Don't know agout refit for electronic pump; however the diaphragm had a slight tear in it so I thought we were home free.
One hour after new pump was put in we went for test ride, engine ran fine but oil still looked diluted however there was not a raise in the level.
The engine is E3 GM 30 F The E is for European I was told

[never monday]

Run it for about 30 min under load and change the oil again.
You have a 3GM30F-YEU. The E means it was built in the Neatherlands.