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Mystery that needs solving. 90hp 3.cyl 2 stroke

H

Harryyabs

New member
I posted a few days ago in regards to a 90hp merc 3 cyl 2 stroke that had leaked fuel into the oil reservoir tank (Im positive).

my initial reaction was to remove the VRO system all together however I’ve been advised that they are reliable and rarely go wrong. The tank was empty around a week ago so I went to go top up the oil and when I got there the tank was full past the last full line that had been marked!

Boat is out the water and I’ve disconnected the tank and drained fluid it smells of fuel but isn’t that viscous.

I removed the 1 way check valve where oil meets fuel pipe and primed the fuel bulb to see if fuel leaks, it does but I have to press the bulb very hard for it to do so.

does anyone anywhere have any idea what might cause this, I have photos that show the level in the overflow pipe on the tank higher a day later than before which suggests pressure is pushing something into the tank.

I’m absolutely stuck and need advice.

cheers

harry

serial: 09758168 (BELGIUM)
 
Last edited:
Oil meets fuel at a Y in the line after it enters the engine compartment. Pressurized fuel comes into the engine only when the bulb is squeezed, or when pressure in the fuel tank might exist....which it shouldn't........mental thought: If you have a closed fuel tank connected to the engine, especially full of gas, and the tank vent is closed, like is the case on portable tanks, and that portable tank gets hot, expanding the gas vapors present, that could force feed fuel.

Otherwise fuel is sucked into the engine and sucked by the Y line where oil enters. The feed from the oil pump output to the fuel line is protected with a check valve so that oil can enter fuel but fuel can't backup through the pump and into the oil tank.

SWAG is that your check valve is no longer checking. How would you test it? My thoughts: Disconnect the oil line from the valve on the oil inlet side and get ready to receive some fuel from the valve. Prime the engine with the squeeze bulb up to and including holding firm pressure on the line for a period of time, rather than stopping when it firms up. If you get fuel in your container you have your smoking gun...bad check valve.

Otherwise I have no idea as there is no physical connection otherwise.
 
I appreciate the response, it may be that I haven’t vented the fuel tank properly. I did actually do a test when I disconnected oil line from check valve and fuel does actually leak through the valve but I have to press fairly hard.

In regards to the fuel can, shall I leave it vented always? I’m just worried to much air will start to cause other issues with the engine if I leave it open when I’m away.

any other ideas would be appreciated though. Cheers.
 
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