BoatU.S. Magazine has recently reported a preliminary investigation into claims about gasoline containing ethanol causing older fiberglass fuel tanks to fail. The ethanol additives could reportedly lead to weakened tank walls and bottoms that potentially could lead to a leak or explosion.

Industry-wide changes in fiberglass resin formulations made in the mid-1980s could be a beneficial ally in correcting this condition. The problem appears only to occur in fiberglass tanks manufactured prior to the changes. It is also important to note that diesel fuel systems do not appear to be affected.

In the preliminary reports, BoatU.S. confirmed the claims of gasoline leaking into the bilge following tank wall failure. The reports also indicated a tar-like substance that produced hard black deposits which destroyed the engine through continual damage to the intake valves and pushrods. BoatU.S. speculates the tar-like substance is created by a chemical reaction between the older fiberglass resin and the ethanol.

Boat owners should be aware of signs of engine backfiring and hard or sluggish starting in which the motor turns over slowly as though the battery is weak. In addition, affected engines may not reach their rated RPM. Chuck Fort, associate editor of Seaworthy, the damage avoidance newsletter from BoatU.S., stated, “Ironically, the substance seems to pass through fuel filters leaving no tell-tale marks – some have appeared clean on our reports. The only way to know for certain is to pull the carburetor and inspect the underside for a black, gummy film which can indicate a serious problem.”

BoatU.S. is recommending all early 1980s or early vessels with fiberglass gas tanks be stored empty over the winter.

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