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gas in oil??????

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bcarli

New member
I have a yamaha 20 hp and I have noticed that slowly the oil on the dip stick is increasing. There seems to be no water intrusion so I am thinking it must be gas but I can not smell any....This is a slow process taking weeks of use to raise the oil on the dip stick a 1/4 to 1/2 inch...
any ideas?
 
I have heard of this before but in motorbike engines. From what I remember is a faulty gasket or faulty fuel bowl float that allowed fuel to leak into cylinder and into oil. also remember reading about engines with this problem suffering some sort of compression lockup and completely wrecking them. This was a few years ago now.
 
Before you say there is no water in the oil, I would pull the crank case drain plug to make sure. There can be water in the oil sitting in the very bottom of the crank case and when you pull the dip stick you would only see oil.
 
Yamaha shipped those motors with 12 pitch props. From my experience there aren't many boats for which an F20 with 12" pitch prop is appropriate. More likely a 10.5 pitch. So what happens is your motor lugs and you compensate with extra throttle and as a result the excess fuel goes buy the rings and into your oil. You need to be able to turn near 6000 rpm. You probably aren't going to put a tach on that motor but you need to go back to your dealer and tell him what is happening and ask if he really thinks you are getting 6000 WOT rpm on the boat you own.
The other possibility is your thermostat could be stuck open and letting the motor run cold and resulting in some condensate from running cold, also if you are trolling a lot there could be some fuel dilution.
Did you run the motor enough with a load during breakin to get the rings seated? Good luck.
 
Thank you all for responding to this for me. I have the engine on a 12 foot hard bottom inflatable. I am the second owner and I know the first owner used the boat a few times and then it basically sat for over a year before I bought it, so I do not know about " breaking it in", however we use it almost daily now. I also was told that there could be a small hole in the fuel pump that would allow gas to enter the oil. I would think I could smell gas in the oil if it was gas but I cannot detect any.
Thanks again
Bill
 
Found out there was no thermostat so the engine never warmed up so the rings never set in right. Have corrected it...and so far the oil level is staying the same...thanks for your input
bill
 
Check that prop pitch too. It is probably ok light but if it is a 12" pitch and you are running much load in the boat I doubt if the motor is turning up like it should. Not good for the long term
 
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