9.9 Mercury 4 stroke Fuel in Oil

[Bullie]

Working on a 9.9 4 Stroke Mercury serial number OR4415xx. I pulled the dipstick and fuel/oil spurted out. I am guessing the fuel pump is the only way for fuel to get in the crankcase?

 

[QBhoy]

There are a few ways.

if you have a thermostat in it that’s not working and engine is running too cold, you can occasionally get fuel washing down past and into the oil.

poor compression can cause the same

running your engine for prolonged time at idle and not under load can sometimes do it too.

on some engines this size, if you lay down or store your engine on its side the wrong way, fuel from the carb can sometimes run through and into the sump. Only on some engines though.

check the compression of your motor and check it’s nothing serious first off.

 

[Bullie]

Ok. I assume I need to get the oil that's in it now out before I spin the engine to check compression?


I was told the motor was idling well and quit when they attempted to throttle up. So, I am thinking the gas got in while it was running. I would say a cup or two of gas/oil spurted out when I removed the dipstick. The engine is on a pontoon boat so it has not been on its side.

 

[QBhoy]

Sounds like it could be a bit serious. If you have that much in the sump it’s overflowing. Check the basics. Check the colour of the plugs, get some fresh oil in it and do a compression test with plugs out and lanyard off. See how you get on.