Fiberglass gas tanks may fail or cause engine damage when filled with gasoline formulated with ethanol, according to damage reports collected by BoatU.S.

BoatU.S. has learned of more than 50 cases of fiberglass gas tanks, many of them manufactured before the mid-1980s, that produced an engine killing sludge or began leaking after being filled with 10% ethanol gasoline.

The investigation is ongoing, but it appears that 10% ethanol gasoline, which was introduced in Long Island and other areas of the Northeast to replace gas additive MTBE in late 2004, may be attacking the resins used in older fiberglass gas tanks. These tanks were standard equipment on some Hatteras and Bertram models and may be present on other boats of the same era. Diesel tanks are not affected.

The engine damage appears to be due to a tar-like substance — possibly from the chemical reaction between the resin and ethanol — causing hard black deposits that damage intake valves and pushrods, ultimately destroying the engine. Early symptoms may include engine backfiring and hard or sluggish starting in which the engine turns over slowly. Affected engines may not reach their rated rpm.

Fuel filters have not captured the substance. The only way to know for certain is to pull the carburetor and inspect the underside for a black, gummy film.

BoatU.S. has also confirmed reports of tank wall failure in some of these tanks in which gasoline was found leaking into the bilge. BoatU.S. has commissioned laboratory experiments to determine the exact cause of the problem. Those results are expected this spring.

New York and Connecticut boat owners have reported the majority of problems, along with one owner in California. Ethanol and MTBE are used to oxygenate gas to reduce harmful emissions. MTBE has been banned in half the states, so some regions now use ethanol blended fuels in its place.

Anyone who has observed or experienced this problem should send details to BoatU.S. via e-mail to cfort@boatus.com.

Boats with fiberglass tanks built before the mid 80's (Bertram, Hatteras, Viking) may be at risk to ethanol eating away at the tanks. The resins work their way through the filters and seperate out when the engines cool down and the gas flashes(evaporates) off internal engine parts. The resins then stick to the engine parts and reharden. The most common problem being that the vales would stick, resulting in bent or broken pushrods. This past summer on Long Island, there were many complaints about problems in newer outboards, especially Yamahas ......here's a link to a thread started on 6/29/04, 27 pages long
http://www.noreast.com/discussion/ViewTopic.cfm?topic_ID=26297&page...

The other scenario with ethanol is that it is an efficient solvent. Therefore, it is cleaning years worth of slime, crud, and varnish that has accumulated in the tanks over that time. Until you are certain that the tanks have been cleaned out, a spare supply of filters and frequent checking would be a good practice.

Lastly, the addition of year round fuel stabilizers would also be a good practice to prevent the ethanol from absorbing water. Also, ethanol gas does not have the same shelf life as straight gasoline and loses it's octane rating if left untreated or unused for long periods of time