fuel in engine oil

[AJK737]

Thought I'd try one more time on this one. My 2004 Volvo Penta 5.0 GL-D (w/stock holley 2 brl.) runs great at/below 4000 RPMs. Above 4000 RPMs it intermittently boggs down - not much RPM change indicated on tach. When I bring the RPMs back down it runs fine again. I am also noticing some fuel in my engine oil. Compression check is good, so I don't believe it's a ring problem. Also had a Volvo Penta dealer do a tune up. They didn't rebuild the carb but thought it was fine. Intsalled new distributor cap and plugs. Few questions for the experts;

Can the carb have a float problem causing too much fuel to enter the carb at high RPM's, leading to flooding and some fuel entering the crank case through blow by?

Can a bad PCV valve cause these problems?

Can contaminated fuel (perhaps water) cause these problems?

Any help would be appreciated.

 

[insttech1]

Re: fuel in engine oil

Interesting....what about a bad valve or timing? Could this push pre-burned fuel mix back up into the top of the head, and allow fuel to get recirculated into the oil?

 

[Maclin]

Re: fuel in engine oil

Inspect the spark plugs. They are a good source of info about what is going on inside the combustion chamber.

To get fuel in the oil takes a bad carb leak, and it would be so flooded when it sat for a while it would be very difficult to start. Those carbs can leak from the fuel directly into the intake manifold thru their internal power valve. But I think you would have the opposite symptoms than what you have now if you have a bad fuel leak.

Yours sounds more like not enough fuel in the carb, or an ignition advance problem, almost like it is in some kind of limited power limp home safe mode.

If too much fuel the plugs will be wet and the engine very hard to start. If not enough fuel then they will be whitish tan.

They should be darker tan with maybe a hint of black soot.

 

[Don S]

Re: fuel in engine oil

Do a compression test. when you pull the plugs out to inspect them.

 

[AJK737]

Re: fuel in engine oil

Thanks guys. I'll pull the plugs and check again, do another compression test, and also check the timing. All the problems seem to be related to the high RPM spectrum, so based on the feedback, I guess it's not likley a carb leak. Can I learn anything about the condition of the valves from the compression check?

 

[Maclin]

Re: fuel in engine oil

An engine can't fake high numbers on a compression test

If some of the numbers are low then a leakdown test would be next, it would tell you if it was valves or headgasket or rings/piston.

 

[NetDoc]

Re: fuel in engine oil

Fuel in the oil sounds like a leaking fuel pump. There is supposed to be a vent from the pump to the carb to eliminate that problem, but I have seen a few with a car style fuel pump installed: they are cheaper. Low fuel volume would also make your carb go way lean at high RPMs, causing it to bog down.

 

[Don S]

Re: fuel in engine oil

Fuel in the oil sounds like a leaking fuel pump. There is supposed to be a vent from the pump to the carb to eliminate that problem, but I have seen a few with a car style fuel pump installed: they are cheaper. Low fuel volume would also make your carb go way lean at high RPMs, causing it to bog down.

He has an electric fuel pump. Not a mechanical pump mounted to the front of the block.

 

[AJK737]

Re: fuel in engine oil

Quick update on this one;

Changed the PCV valve - Old one seemed OK, but did allow some air flow from carb to valve cover.

Did a compression check (Warm motor, all pulgs out, throttle full open) - All cylendars between 192 and 205.

Checked the new plugs that were installed (have about 45 minutes of operation on them) - All looked mostly normal, but three of them had more carbon (black) than the others. None were wet.

Did notice a small leak in the carburetor diaphram, so pulled the carb and having it rebuilt.

Will keep you posted.