My 336D has been having issues lately. Will start and run for about 15 minutes and then the rpm's will die down to almost nothing and the engine will quit. Will not restart or if it does on occasion it will barely run at an idle but if I put it in gear will die again. Have not been able to figure out what is going on with it except maybe it is overheating. Perhaps the thermostat is not opening. Does this sound like the problem to any of you that are much more experienced than I am? If so, What thermostat does it use and where do you find one? Thanks for the suggestions