All RB211 in 747's and Tristar had automatic fuel heat from the FCOC - fuel cooled oil cooler. JT9 had manually controlled fuel heat with switches on F/E panel. I was once slightly involved with an incident where the F/E on a 727 had the fuel heat selected on take off - the fuel into the engine overheated and on reducing power went sub idle causing all three generators to trip off - fortunately it was daylight and he managed to land with no further incident. On Pratts advice all 3 engines were replaced. Expensive error.