I use to have Ext Temp in my old car to watch out the temps. Make sure the mixture not too lean to melt the head or seize the engine. It's also help for tuning the car but not too good. Because the temp from the probe is not respond fast enough. Air-Fuel Ratio meter is better. The best is hookup computer to the car and see the real time. I think 1100 F-1200 F is the safe range not go over 1350 F. Not sure about the number so Don't quote me on this.