I have a lanair..this is the second year of operation...the build up is from excessive parrafin in the oils IE valvoline = worst quakerstate = second worst. the prehaeter gets to 140 f and the parrafin is separating out at THAT cool of temp??!! whats happening inside the engine? I already know..there is NEVER any smoke comming from the vent pipe, ar EPA approved except california ( farting is illegal in california ) AND provide excellent heat. gear oil will not burn well, transmission fluid and less to non parifin oils burn well IE pennzoil / castrol etc. A little carb cleaner and a few tools you can clean one carefully with full dissassembly in about an hour..and thats a full dissassembley...usually just unscrew the tip and clean and you cookin again.