Fuel leaking into oil crankcase

[HTBaggett]

Originally Posted by shakey doug

I note that you mention having the HP fuel pump is it possible to post a list of work carried out & parts used. Main suspects given other work already done would have be bad pump element or bottom delivery valve joint.

Shakes Doug,

Thank you for your input. It’s actually doing the same thing as before all the attempts to fix. I just don’t think it was anything done so far.

HTB

[HTBaggett]

Originally Posted by Jesse

Faulty return to tank line is a possibility worth checking. I've encountered it twice and both times it was after recent work on fuel system.

Jesse,

I have replaced the fuel return line, but Thanks for your input.

HTB

[Mike Banks]

Several things could cause this. This is my order of likelihood and expense.

Fuel pump diaphragm leaking.

Cylinder head gasket leaking--any evidence of misfiring or uneven running?

Cracked cylinder head.

[HTBaggett]

Originally Posted by jimbunyard

Don't know why this stuff seems to run in spells, but I changed 3 gallons of diesel out of a 6.6 Isuzu crankcase yesterday...but that's a story for a different thread.

This is a little strange.

Does the engine run well, with no starting, full RPM or power problems?

If it does, I would make sure that the new lift pump isn't defective, and that it is correct for the application.

As far as I know, the injection pump on this engine doesn't have any rubber seals that seal the diesel injection side from the crankcase. The delivery valves would leak to the exterior, probably the only ultimate source for diesel to get into the crankcase from the injection pump would be the copper gasket (item 6 below), where it would enter the crankcase via either the rack/pinion (14/26) interface, or between the pump body and the guide plunger (18). Re-use instead of replacing the #6 gasket could cause a leak, as could dirt or faulty pump assembly---but the engine probably wouldn't run very well if that is the case.

Seems a case of simplest first (check the lift pump), then bring the injection pump back to the rebuilders. There doesn't seem to be any other real candidates for where that amount of fuel can come from in that amount of time, at least not to my eyes...

Jimbunyard,

Thank you for your extended input. The engine starts right up and runs great. It does slow a bit when I engage the transmission, but nothing special.

The injection pump could be the issue but I had it professionally rebuilt. Hopefully they inspected it for damage and cracks prior to rebuilding. They were supposed to replace all damaged/wear parts and test before returning it to me for operation. I was charged based on the necessary parts and labor.

I and convinced the lift pump is fine. I isolated it completely with an electric fuel pump.

[Wulf]

Check if retainers (#12) are tight. These sometimes loosen if HP injection lines are loosened without holding the retainer with a second wrench. If not tight fuel will bypass internally in the HP pump and end up in the crankcase. I found this on one boat (Yanmar too by the way but can happen on others as well) while in Mexico. Owner was ready to pull his hair out...tightened all up, no more problems. Easy to check.

Originally Posted by HTBaggett

Jimbunyard,

Thank you for your extended input. The engine starts right up and runs great. It does slow a bit when I engage the transmission, but nothing special.

The injection pump could be the issue but I had it professionally rebuilt. Hopefully they inspected it for damage and cracks prior to rebuilding. They were supposed to replace all damaged/wear parts and test before returning it to me for operation. I was charged based on the necessary parts and labor.

I and convinced the lift pump is fine. I isolated it completely with an electric fuel pump.

[scallowayuk]

hi, most comments are coming back to the lift pump. i know you have checked replaced but it is the most obvious likely problem as youre engine starts so well , so no compression problems hence no cracks in head. i had this problem and it was a small split in the lift pump diaphram . when fuel was pumping under pressure it passed through the split straight into the sump, not all lift pumps have a hole in the bottom and even if they do as my did they become blocked and fuel cant drain into the sump regards

[Jimgreen8c]

It's easy to check the fuel pump. Remove the pump. Cap the output end. Pump fuel using a cheap hand pump into the input side. If the fuel pump diaphram has a hole in it, fuel will leak our of the area where the lever goes into the crankcase.Move the lever slowly and gently . If no leak, the only other place Fuel oil can get into the crankcase is the injector pump assembly. Again it can be checked, but it's harder to do. It is usually the fuel lift pump diaphram.

[RaymondR]

Originally Posted by jimbunyard

Umm, the pump in the diagram is the pump on the engine if you have a 2gm20. The 2gm10, 15, and 30 have the same style pumps. There is no rotating shaft, nor are there rubber seals internally.

Whilst the above is true my recollection of the pumps on this series of engines is that the high pressure pumps are actually located inside the body of the engine and I think are driven by cam lobes on the camshaft itself. Consequently the two most probable leakage points for diesel into the lube oil are the camshaft driven fuel lift pump diaphragm or a leak down through the HP pump plungers.