Another DF-90 Gas in Oil Problem

[l3rian]

So my 2008 DF90 is making oil. Actually it is getting fuel into the oil. It is definitely fuel and not water (not milky or discolored, and smells like gas). About 6 months ago this all began. The motor was running bad, and actually cut off on me. I got it back to the dock, pulled it out of the water and notcied oil running out of the prop when I trimmed the motor down to drain it. Took it straight to the shop and was told the culprit was a faulty low pressure ful pump caused by a pinched fuel line by an improperly installed zip tie. Parts replaced, oil changed, all good... Almost.

I work out of town for long stretches, so it sat a while, but with fresh non-ethanol gas and marine stabil in it. It was ran on the muffs at least every 3-4 weeks or so.

Get home, check the oil and its high. Took it back to the shop and had the fuel pump replaced again under warranty (sort of). Got it back and took it out. It was high again. Drained some oil out to get it within range. Now it has been fluctuating. I check it every time before and after I run it. I took it out a week ago. Was within range when I left. Got home, flushed, checked the oil the next morning and high again. From what I have read on here and all over, outboards are made to run hard and if they aren't up to temp they make oil. I dont't like this explanation, but i was doing a lot of slow running looking for bait and trolling last time and the oil rose. Today i decided to test the theory. I checked the thermostat in the house on the stove and it opened and closed as it should at the correct temp. (or as close as I could get it with a dollar store meat thermometer). took it out on the lake by the house and ran it pretty hard for about 25-30 minutes. Ran it at about 4800 rpm mostly with a few WOT stints in there. Came home, let it sit about a half an hour and checked the oil. PERFECT.

BTW the engine has less than 200 hours on it and had good compression in all cyclinders the first time it was in the shop.


so i guess my question is WTF? cause that's all I know to ask... lol

But seriously, I have the engine level every time it check the oil. Anything else that can cause it? another mechanic mentioned the VST. How could that introduce fuel into the crankcase?

Thanks for sticking with me on that long post, I'm just frustrated.

[redlowrey]

I have often wondered what would happen if the float in the vst stuck and the chamber filled with fuel instead of staying at the right height, because the vapour hose is at the top of the vst. No engine will make fuel in the oil unless the cylinder is not firing, even if you left the thermostat out and the engine operating temp was low the ecu would see a higher temp signal line voltage and the engine would run richer. There will be some soot blown past the rings but no way fill the sump with fuel.

[l3rian]

Thanks for your reply. I agree with you that it should not get that much gas past the rings. But I should also mention that it ruins perfectly fine except for that one first incident where the crankcase was completely full. ki and when I ran it hard yesterday, the oil level was high before I ran it and dropped back down to normal after I ran it. Apparently getting it nice and warm is enough to boil off the gas and leave the oil. I will admit I really have no understanding of what the vapor separator actually does. But your reply has made me more comfortable with the mechanic who wants to troubleshoot it and not like I'm wasting even more money.

[redlowrey]

The vapour separator is supplied fuel from the low pressure fuel pump inside the chamber. the fuel is maintained at a certain height with a float and needle and seat and the high pressure pump is also installed in the vst. The high pressure pump is duty cycled by the ecu and pumps the fuel out of the vst through the high pressure fuel filter fuel rail, injectors pressure regulator and dumps the excess fuel inside the vst, the only job the low pressure pump has is to keep the supply up. What I am saying is if the float stuck and fuel rose up in the chamber it might get sucked into the engine via the vapour line, it wouldn't affect engine performance.

[redlowrey]

There should have been a commer where I had pump, the low pressure pump is mounted on the engine.