Mooney Operators Report Leakage, Paint Issues After Using G100UL

General Aviation Modifications Inc. is inviting an operator of a wet-wing Mooney to visit its Ada, Oklahoma for a borescope inspection to assess the condition of the sealant in the tanks. "I would like to have the chance to borescope an older Mooney fuel tank that has not been converted over to a bladder," Braly said in post on mooneyspace.com. The invitation was extended after two California owners reported issues with fuel leakage after putting GAMI's G100UL in the tanks. The fuel is available at three California airports.

Mooneys and many Pipers were not factory equipped with rubber bladders in their fuel tanks. They were formed in the structure of the wing and a sealant used to fill the voids and rivet holes in the metal. Many older Mooneys started leaking when 100LL was introduced and owners either installed bladders or had the tanks resealed with a "sloshing" treatment developed in response to the widespread problem.

One of the owners reported on mooneyspace.com that his tanks started leaking a week after he started using G100UL. Another said his tanks had been seeping (within manufacturers limits) but when he added G100UL the paint blistered in the areas affected by the seepage. GAMI founder George Braly told AVweb it's not clear what role, if any, the fuel is playing in the issues but he did say the formulation is different from 100LL, notably in its use of an aromatic amine called Xylene to boost the octane and hence detonation resistance of the fuel. Aromatic amines are solvents but Braly said in a detailed response to the posts it's the least aggressive of the octane boosting chemicals. He also noted that the sealant in the tanks is likely decades old. "It lasts a long time but it doesn't last forever," he said.

Braly said the fuel has been exhaustively tested on sealants, seals and gaskets used in airplanes under the supervision of the FAA. He also said he's never seen it cause paint to peel. If spills are not cleaned up, it can cause a yellowish tan stain. Many of the responses to the thread on the forum said they were not having any problems with G100UL.