4.3 liter engine problem
 

i just bought a mariah from my buddy. it has 4.3 liter mercruiser in it. after we run it hard for a couple of hours it seems to get fuel in the oil, we took it to the shop and they tell us nothing is wrong with it. this has happened several times. any help would be great. thanks guys...

Re: 4.3 liter engine problem
 

Assuming that you have a mechanical fuel pump, it sounds like a leak in the diaphragm of your fuel pump is causing the problem. Because one side of the pump diaphragm contains fuel under pressure and the other side is connected to the crankcase of the engine, if the diaphragm splits (a common failure), it can leak fuel into the crankcase.
It's also possible that raw fuel is getting past worn piston rings (blowby) but any amount via that method would be very small so i would suspect the fuel pump diaphragm first.