Viton / FKM / FPM / Fluorosilicone

Viton is a trade name for a type of fluorocarbon rubber developed by DuPont specifically for the aerospace industry. The ASTM in the USA uses FKM as the generic term, but DIN/ISO in Europe and the rest of the world prefer FPM. It is often the most expensive of the three rubber types discussed here. FKM is compatible with petroleum fluids (including dino and synthetic lubricants, pure gasoline, and diesel). FKM is also fully compatible with water and ethylene glycol coolants. Most FKM grades are also a little better than NBR at handling biodiesel and ethanol-blended fuels, although FKM is still not the best choice for ethanol -- and it is a downright poor choice for nitromethane. Its high 400F operating temperature makes FKM a better choice for sealing engine, transmission, and differential oil systems.