Mercury oil injection draining into gas tank

[pmarz]

Hello, I just recently purchased a boat with a 1989 Mercury 40hp classic oil injection outboard on it. The previous owner told me to unplug the gas line when you stop or all the oil in the oil tank will flow into the gas tank. Does anyone have any idea what would cause this?

 

[critchfielda]

I have the reverse problem on the same motor, only a 1990. I have gasoline entering the oil tank, seemingly when under power, but possibly also at rest.

 

[Faztbullet]

Check valve (oil) on fuel pump

 

[QBhoy]

Yeah...there should be a N/R valve piece on the oil pipe to carbs just before they split.
Jeez, she must be smoky !
I'd be inclined to disconnect the oil pump and pre mix.
Had a really bad day out once with a big 200hp Merc oil injection failing.
Resulted in a crank shaft out the side of the block at 70mph and a few thousand on a new engine.

 

[QBhoy]

Not crank shaft....rod even !

 

[pmarz]

Thanks, I've had her out a few times and haven't had a problem but I carry extra gas and oil. I think I'm just going to disconnect the oil pump and premix.

 

[Bocastan]

I have a 150 Mercury carberated and I found 2 stroke oil in the ball and water separator so l guess I should look for a defective check valve in the oil line ? The 2 stroke tank on the engine is also not full.