Getting Gas In Oil

[ccampbe1]

What would cause me to be getting gas in my crankcase? I have a 2003 225 Yamaha 4 Stroke.

[boats.net]

Bad fuel pump, VST overflowing, engine not turning enough RPM's, engine running too cold or getting past piston rings.

[ccampbe1]

Ok, how would I go about figuring out which is the problem without just changing parts?

[rodbolt17]

bad fuel pump, not gonna happen.
VST needle leaking, possible but not likely, the VST vents to the intake.

over propped for the load THAT day, very possible.

any LOAD you run with the engine MUST be capeable of 5700+ RPM.

stuck open Thermostats yep that can do iot.

extended idle with no WOT time can as well.

now the expensive one.
ring gap alighnment.
if the gaps on a piston ring alighn you get fuel in the oil.
can be easily found with a leak down test.

you can test all 6 cylinders in about 20 minutes.

[ccampbe1]

Thanks. With my luck it will probably be the last one. Don't think it will be the prop because the starboard motor is proped the same and isn't doing it. I rarely run either motors over 4500 Rpms . I will try a new thermastat and see what happens and if it still happens I will get a leak down test done. Thanks for the info.