i have an 85 70hp evinrude motor. after running and then sitting for a while it leaks what appears to be fuel oil mixture coming from the lower unit around the prop shaft. the oil leaked is black as can be. I dont believe it's gear oil as the gear oil has been changed a couple times and still looks like new. Any input would be appreciated, Thanks
What you said. Unburned fuel draining from the exhaust where it picked up black particles of carbon, turning it black. (The exhaust goes out through the prop hub). This is often a result of long periods of slow running OR running on muffs in the driveway. Good guess??
What's your oil mixture? As Gator stated, continuous low speed operating will create more buildup. VRO's or variable ratio oiling was created to avoid this by providing leaner ratios at low speed. Your motor was supposedly engineered to run at a claimed 100 to 1 mixing ratio by Johnson Evinrude but with cheaper grade oils that is a risky proposition. The only oil that I have trusted at that ratio and have used for many years is Amsoil 100% synthetic. Their100 to 1 product was made available to the public in the late 70s. Many techs on this and other forums scorn it's use at that ratio, but none of them, I assure you, have the experience using it as long and using it as successfully as I have. These two 80's vintage 30s in the background have been 100:1 Amsoil since first tank. Used constantly WOT for frieghting in remote NW Ontario. After 30 years one was stolen from my shed, the other has no mate, so it just sits now until I can find it a partner.
