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Safety Warning - Fiberglass Tanks and Alcohol-Blended Fuels Donít Mix

The following is a summary of an account submitted by EAA member Dave Brents which relates the extensive damage to a Rotax 912 engine attributed to the use of a fiberglass fuel tank exposed to alcohol-blended fuel. Because the damage was so quick and extensive, it’s important to remind all builders the seriousness of this problem. Fortunately no one was hurt, but a brand-new Rotax 912 engine was damaged to the tune of about $10,000. The account was drawn from postings to the Rans S7 Courier builders and flyers Yahoo discussion group with the subject line, “This Rotax 912 is already broken in.”

The Rans S7 builder seemed to have problems with his new engine almost from the very start. It was hard to start, backfired, and occasionally made sounds which caused the builder to be concerned about the possibility of some major mechanical problem. After only about one to two hours of running for lifter tests, leak check, and carburetor synch, and about one month after the first engine run, it stopped and wouldn’t turn over anymore. Cylinders #2 and #3 had zero compression. The Rotax 912 was examined by Lockwood Aviation and found to have ruined valves, ruined pistons, and bent pushrods.

The cause was a mystery at first and thought to be due to overspeeding or perhaps a tachometer error. During a full rebuild, it was found the intake valves were stuck so tight they had to be driven out with a hammer. The valve stems were coated with a black resin. The intake valves had hit the pistons, push rods were bent, cam ruined, and the gearbox dog gear ruined. The exhaust valves were fine.

Then the builder realized what had happened. He had installed a custom-built fiberglass header tank. His own words say it best. “I think ethanol and a fiberglass header tank could be the reasons my 912 was destroyed. I sumped the fuel system two or three days after I first ran the engine. I crawled under the fuselage and opened up the fuel drain valve immediately below the header tank. Imagine my horror as I saw emerging from the open drain not a steady clear stream of gas, but a trail of viscous, gooey-brown ‘snot.’ I immediately realized that the tank’s fiberglass resin must be dissolving in the gasoline, and the brown goo was settling to the bottom of the tank where it will inevitably find its way to the engine. So I removed that header tank right away and later replaced it with a similar tank fashioned out of aluminum. Unfortunately it was too late - by that time the engine had already eaten enough brown goo to cause damage. I did not realize this until it was too late. The engine felt funny to me when I turned it by hand, but I thought that was normal because of the gearbox and clutch.”

The manufacturer of the fiberglass tank stated that the epoxy resin used for its construction was supposed to be fuel resistant and offered a full refund to all its customers. Many manufacturers, including Rans, have moved entirely to plastic or aluminum fuel tanks. Since we would prefer our fuel tanks to last the life of the airframe and we cannot predict what additives might be in our fuel in the future, extreme caution about fuel tank selection is advised. Alcohol-blended fuels should be avoided if possible.

This story ends on a happy note. The builder installed the rebuilt engine, the aircraft passed the airworthiness inspection, and the first successful test flight was completed in early February 2010.

See a related story about Alcohol Fuels in Ultralights and Lightplanes in the December 2009 issue of Light Plane World.

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