Yamaha 8HP 4stroke kicker making oil

casper5280

Crew Member
Just went and checked all my fluid levels in the boat and the kicker oil level is quite high. I remember there was a thread about this and I thought it was just the bigger motors doing this. Any clues on what to check or fix. Can't find the thread relating to this. thanks for any help.
 
Usually when an engine is running to cold the fuel entering the cylinders isn't completely burned off and the residue slips past the rings and enters the crankcase. That unused fuel mixes with the oil and over time will raise the oil level in the crankcase. If this goes on too long the fuel will dilute the oil to the point where some lubrication qualities are lost and moving parts could start to show signs of friction damage. Not a problem with 2 strokes obviously, quite common in 4 stroke kickers when a t-stat sticks open. Another way for a crankcase to fill up with fuel is when a fuel pump diaphragm develops a tear and raw fuel passes past the diaphragm and directly into the oil reservoir. This will fill the crankcase quickly.

words from Profisher


 
Yep. on these smaller Yamaha engines it is a fairly common problem. I always carry a spare fuel pump and a t-stat so I can make quick same day repairs. Both are very easy fixes. I bought into the higher cost of keeping a complete spare pump over just the diaphragm simply because it is way faster to change out a complete pump dockside than to break open the pump and change the diaphragm. If you take your boat home every night I would just buy a spare diaphragm and make that repair at home.
 
Quite likely, your oil has been diluted with fuel. Did you follow a break in procedure to help seat the rings? A carburated engine may need to have its mixture screw turned down ( if it even has one ). Incomplete combustion allows fuel to go past the rings diluting the oil. It gradually worsens as the diluted oil no longer provides a good sealing medium. Prolonged idling exacerbates this condition. You might want to check the thermostat operation as the raw water might never get hot enough to "boil off" the raw gas.
 
Once raw fuel enters the crankcase it will never "boil off". An engine even when operating at normal temps never reaches temps high enough to do that. Over long periods of time gas exposed to the atmosphere will evaporate but once mixed with oil it is pretty much there to stay.
 
I have had the same problem several times on my 9.9 Yammi-the guys are right on-fuel pump leakage or T-stat-either will do it. Not a big problem to fix.
 
Thanks on the way to the parts store I guess. 1 Hour in and I already have the problem diagnosed.
 
Spent a lot of time and money on a 9.9 Yami HT with this problem and there are many causes. In my case it was the carb and not the fuel pump or t-stat. etc. that turned out to be the problem in the end.
 
What ars the opinions to running a hotter thermostat temp as these engines typically are at fairly low rpm? Guys with Honda kickers seem to do that often.
 
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