Yamaha 4 strokes getting fuel in the oil

24 Albemarle

Seaman
Joined
Jul 30, 2008
Messages
54
Over the last 4 months I've worked on four yamaha's 50, 60 and 70 hp all made in the last 7 or 8 years with oil saturated with gas. One fellow had gotten some E85 and it literaly disolved his fuel pump diaphram and let fuel directly into his valve cover through the fuel pump until it was ready to hydraulic itself to pieces, when I pulled his dipstick it blew oil all over me,him and the boat. Another was a stuck thermostat (stuck open) motor wouldn't heat up computer said more fuel and injectors oblidged until it bypassed rings into crankcase raising oil level to critical. Other two had injectors stuck open and sprayed continuosly until high oil level was detected.The last two motors ran well right up to the point of discovery of high oil level. We are on the east coast and are being fed a diet of 10% ethanol (so they say) and I have tried to search this forum for others with similar experiences and have not seen any... I have a hard time believing I am just the only guy to come across this as I only do 20 or 30 a year what must a dealer or big shop be experiencing? Anyone?
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Here in the Midwest we've used E10 fuel for decades and simply do not have the issues you speak of. A ruptured fuel pump diaphragm does not necessarily point to E10 fuel as most four strokes are new enough to have ethanol tolerant fuel system components. All of the other problems you mentioned are not fuel related -- they are mechanical issues. Making oil is a problem on some engines but the two main reasons seem to be running too cool or running the wrong prop (one with too much pitch).
 

GA_Boater

Honorary Moderator Emeritus
Joined
May 24, 2011
Messages
49,038
Actually all but one of the problems are mechanical problems. A bad thermostat and stuck injectors are mechanical. Fueling a marine motor with E85 is operator error, but maybe that is mechanical too since it ate the fuel pump diaphragm. None can be blamed on E-Fuel.
 

24 Albemarle

Seaman
Joined
Jul 30, 2008
Messages
54
I agree on 10% alcohol now bring sold is working with these engines, the one I referred to came from Delaware and they sell e85 there, now I cannot say that's what dissolved the diaphragm, not ruptured but literally disintegrated the perimeter of the rubber at the drive disc. The one I did yesterday has working thermostat (verified w/ thermometer)In about10 hours run time made half a quart. motor has 140 hours. Runs perfectly and has whatever pitch prop Carolina skiff Dealers sell w/package.
I'll ask him what she turns, I didn't run it out. I did notice it was an aluminum that had seen the rougher side of an Eastern Shore oyster bed, at one time or another.
Anyway I wasn't really inferring that the specific fuel was causal, but it's physical presence in the oil is disturbing. BTW Plugs looked perfect and motor ran great, according to owner.
So, it could be too cold, injector stuck open, rings not seated or fuel pump breached, or over loading engine with prop. About right? Thanks,
 
Top