Like Corse - R said, every engine is different. For instance, my rsr4 rtr3 .15fe engine can go up to 280-290 degrees (thats info is straight from hpi themselves). The new engine i have for my ntc3 is a mugen mr12 and the guy i bought it from said dont go over 220. Some guys at a track I race at told me to try not to go over 250 since 250 degrees is boiling. I've run my rs4 rtr3 up to 275 with no problems but i try to keep all my engines around 250 give or take.