Mercury 25 4 Stroke. Gas In Oil

[LittleRedFisherman]

FishinWrench and others, looking for some help. I noticed before my last couple smallmouth trips that when I checked the oil, it was plum full to the top of the stick, the oil was thin and smelled of gas. So I changed the oil and filter and went fishing, it didn't seem to me to accumulate any more that time. I fished again with it a week later, and now it's sat for a couple weeks. I checked it earlier today and it was full again. Not sure if I got it setting there, or from my second trip? I talked to a local tech guy and he said there's a diaphragm in the fuel pump that will bust and put gas in the oil. I'm also wondering if leaving the gas hooked up in the hot sun would cause this. I"ve had my shop full working on harvest equipment and the boat has been setting out the past week in the heat. I'm wanting to look at the diaphragm, wondering if anybody can tell me from these pics where to look for it, or am I barking up the wrong tree? thanks for the help. Bret.

[fishinwrench]

"Making oil" as it is called, is a pretty common ailment with 4-strokes. Obviously either water, raw fuel, or both is entering the crankcase and floating the oil level up.

Determining where it's coming from is the first step.

Remove the two screws holding the fuel pickup pump to the block but leave the other two that hold the fuel pump components together in place. Then while squeezing the primer bulb tightly look for any fuel exiting the vacuum side of the fuel pump (Careful...don't let it squirt you in the face).

Report back with your findings and we'll take it to the next step.

[LittleRedFisherman]

Thanks wrench I'll check this out and get back

[bfishn]

An unvented fuel tank can cause that.

[fishinwrench]

An unvented fuel tank can cause that.

On a carb motor, yeah. Pressure can build up enough to blow the needles off the seats. But not likely with a EFI system that's designed for higher fuel pressure.

[LittleRedFisherman]

On a carb motor, yeah. Pressure can build up enough to blow the needles off the seats. But not likely with a EFI system that's designed for higher fuel pressure.

The tank is vented properly looks like. Wrench, where in those photos is the fuel pump I need to take off?

[fishinwrench]

#1 in this diagram

[LittleRedFisherman]

ok thanks, i'll get on it tomorrow and holler back!

[LittleRedFisherman]

Wrench, took the pump off like this and pumped on bubble pretty tight. No leaks

[fishinwrench]

Ok. Next step is to change the oil/filter only filling to the 1/2 area on the dipstick, go for a nice long slow cruise (idle to 1/2 throttle with no 3/4 to full throttle operation), allow engine to cool, then take note of the oil level.

THEN.... Go for a nice long balls-to-the-wall (wide open) cruise, allow to cool and check again.

If the level rises at an idle....then falls back to where it was during high speed/heavy load use then the factory techs claim that either the piston rings have not seated yet, or the engine was not broken-in correctly.

If the oil level continues to rise regardless of how it is run then it's time to sell it and buy a 2-stroke...because you won't be willing to pay what it will take to fix it.... Or just continue to run it and change oil about as often as you trim your fingernails, or at least before it blows out the dipstick tube. Don't just drain it down because the oil is being thinned/diluted.

(So much for "clean/green running engines", right?)

Some techs are blaming the use of synthetic oil, but I'm not even gonna weigh-in on that one.

Bottom line; There is no reasonable ($$$$) repair that can be made.

All of the above is assuming that it IS FUEL and not water. If there's water in the oil then we need to troubleshoot differently.