Temps can be very deceiving. We once ran an engine on our test stand and measured the temperature at the rear of the cylinder head, where the aluminum was smooth. We used a contact probe and measured 375-degrees F. The engine was an O.S. Max .40 FP, and was running on Cool Power fuel with 10% nitromethane. We did our testing at full throttle with the mixture leaned to peak RPM. The engine would run "all day" like that. After a few hours' worth of running, we stopped and examined the engine and found absolutely nothing wrong with it. That engine was used on the shop's radio test airplane for several years before a crash into some very hard ground put an end to it.

We find that if you rely on temperatures to set an engine's needle valve, your engine will have a very short service life.