If you’re like a lot of fishermen who use outboards you should pay attention to this, because you probably get your fuel at the local service station when you gas up the pickup. In most cases that means you have been using a mixture of 90 percent gasoline and 10 percent ethanol, or E10 as that mixture is called.
The benefit of combining ethanol — made from things like sugar cane and corn — with gasoline is that the combined product produces a better burn and thus reduces air emissions.
The E10 combination probably hasn’t been a problem if you have a fairly new outboard, as the more recent models have been tested to run successfully with E10.
But they have not been tested to run on a mixture with 15 percent ethanol, and as of Jan. 21, 2011, the Environmental Protection Agency said the use of ethanol in gasoline could be jacked up to 15 percent. It will probably be a couple of years before outboards are tested for E15.
The problem is that ethanol is a solvent, and increasing the mixture by 50 percent could adversely affect an engine’s fuel lines, fuel tanks, pumps, injectors, carburetors, valves, O-rings, and gaskets.
Even assuming E15 doesn’t damage those engine components, if it remains too long in the fuel tank or even the carburetor, you can have the same problem you would have had with E10 — phase separation. That’s when ethanol, which absorbs water and holds it in suspension, takes on too much moisture. Then the ethanol-water mixture drops out of the fuel. It settles on the bottom of the tank and is sucked into the engine.
If the separation takes place in the carburetor, the bowl can corrode. On a 4-stroke the mixture could gum up and corrode the small passages in the carburetor to the extent that the carburetor can’t be repaired.
There is a way to avoid ruining a perfectly good outboard: Buy your outboard fuel at the marina, not the local service station. The EPA waiver allows the use of E15 only with newer cars and lightweight trucks and is not permitted to be used in boats, which is why the Coast Guard recommends you only use gasoline purchased at marinas.