2006 Yamaha T8 Gas in Oil ( crankcase )

the fog ducker

the fog ducker

Well-Known Member
so , this motor has been babied , religiously serviced , good solid compression still ,
will do a test later today , motor ran ok all summer , but twice it started to burp and fart ,
check the oil , was very full , very thinned out and smelled like gas ,
im reading a common problem , ran this motor since new ,never full bore , but days of heavy rpm in the wind and current , i would drain the oil and refill with 500 ml only , says ta use 800 ml , but kept it lower so wouldnt refill so fast , about after about 30-40 hrs of use , it would overfill and start to run poorly , especially at lower rpm , ive heard this is a common problem , i ran it pretty hard last outting to try and reseat the rings , still making oil though , any suggestions ?? ring job ?? motor still looks new , fires instanly , no oil burnage , worth fixing ?

thx in advance

felix
 
too many hours at troll = never getting hot enough for complete fuel burn.
soumds like you're doing everything right, try running 5-10 mins at wot at end of the trip.

:)
 
It is true they will make oil trolling but if it is making it quickly and its puking out of the dipstick tube guaranteed it the fuel pump.
 
I also had the same problem and changed out the thermostat and it fixed the problem.
 
When the crankcase fills quickly it is the fuel pump diaphragm, and when it fills slower it is the t-stat. No need to check compression just replace the t-stat. Running cold and not burning all the fuel properly.
 
I had the same problem on my T8 a couple of years ago. Thermostat was stuck open. Replaced the thermostat and problem was gone.
 
I have run marked fuel since I had my own boat at 13 years old and every outboard since. No issues.
 
If your making oil regardless of fuel pump or thermostat or carbs fix right away as it may if left for to long glaze the cylinder walls resulting in complete rebuild...ask me how I know this....
 
If you aren't in the habit of checking your oil regulary it should tell you that your crankcase is overfilled by running crappy (mostly irradic speed). and you will notice a fuel/oil sheen in the wake of your boat as it slowly pukes out the excess into the water.
 
Most likely the engine is running cold, a thermostat that is stuck in the open position will not allow the motor to come up to full temperature. This will allow fuel to get past the piston rings and into the crankcase. Using marked fuel compounds this problem due to the engine not being able to burn the added dyes. Another cause as suggested is a hole in the diaphram of the mechanical fuel pump, alowing fuel to be pumped into the crankcase. Using Ring-free, as suggested by Yamaha can also do wonders on a motor that's run at a constant lower rpm in our cool westcoast environment.
 
The only difference between an engine not running up to temperature and allowing either marked or unmarked fuel past the rings is that you will see the dyed fuel colour in the oil with an engine using marked gas and and the oil with an engine burning regular fuel will just be diluted. Both are allowing fuel into the crankcase and the dye has no relevance to this.
 
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