Outboards “making” oil

[brutus]

Yes, the dye makes it easy to see when fuel has entered the crankcase oil but it’s not the cause of fuel getting past the rings.
There is a Vancouver Island Yamaha dealer who “guarantees “ that it’s only marked gas that causes this problem. He is emphatic - and he is wrong!

Agreed,from my research(resent) cause my new to me suke, I s making oil, there is always a 10-15% tolerance of fuel in the oil without serious catastrophic failure, but when your making a litre every 30-50 hrs it can’t be good, mine is down to about a 1/4 litre every 40-50 hrs, when it gets there I just change the oil

 

[Samnjoe]

Yes, this is a common problem with four stroke outboards running in cold water. The engines run cold because the manufacturers install cold thermostats to help prevent salt buildup due to high temps. This makes for poor piston ring expansion (bad ring seat) and engine compression squeezes fuel past the rings and into the crankcase. I had Yamaha tell me that this was “ no big deal”. BS. Ask any engine builder if diluting your engine oil with a solvent (gasoline) is no big deal!
Piston ring expansion (ring seat) is improved when temps are allowed to increase. Engines like to run warm. Unless they have changed over the past few years, Yamaha runs cold thermostats. My F300 had 140F thermostats. I switched to Suzuki thermostats (170F) and the problem disappeared. It does help to run the engine hard now and then to help seat the rings, especially when the engine is new. The recommended break in procedures of babying the engine and running with cold thermostats is a recipe for poor ring seating. It would be better to warm the engine up while running gently and then romp on it for short periods.
By the way, that theory of the dye in marked gas causing the problem ( as spouted continually by one of the local Yamaha dealers) is total BS!

I agree the dye theory is BS but if you are making oil that oil will take on the color of the dye. Mine used to look like ATF when I changed it.

 

[scott craven]

Agreed,from my research(resent) cause my new to me suke, I s making oil, there is always a 10-15% tolerance of fuel in the oil without serious catastrophic failure, but when your making a litre every 30-50 hrs it can’t be good, mine is down to about a 1/4 litre every 40-50 hrs, when it gets there I just change the oil

Did you try the colder running thermostat already ?

 

[trophywife]

Did you try the colder running thermostat already ?

hotter, lol

 

[scott craven]

hotter, lol

Right, I must be dyslexic

 

[brutus]

Did you try the colder running thermostat already ?

I am running the hottest thermostat suke makes, my issues is carbon built up from trolling hrs on the engine, running ring free seams to help so far

 

[brutus]

hotter, lol

Coming from @trophywife hot hot hot

 

[Doubleheader]

I am running the hottest thermostat suke makes, my issues is carbon built up from trolling hrs on the engine, running ring free seams to help so far

Always been a thing with every zuke I’ve had, and I rarely troll on the main. Can of sea foam or any other similar product in the crankcase prior to oil change does the trick. I’ve even used diesel and atf, take it for a rip and drain it when it’s hot. Started winterizing by adding a can to the racor and crankcase, idling until she starts smoking and shut er off. Warm up and replace fluids in the spring. I stopped adding anything to the fuel tank during the season, didn’t find it helped.