Good question....I hooked my vapor coolant gauge to the coolant line coming from the head so that it will read the temp of the coolant coming from the head. Then I set my warning light on my vapor to 175* & my danger light @ 190*. My reason for setting them at that temp was cause my motor averaged 150* when I'm riding it normally without keeping it under load for long periods of time. I'm not saying that's the best temp to set you're at but that was with my vapor using my old 421 cub cylinders. So it might be different for stock cylinders, jetting & etc. hope that helps. Reek.