When I drove my 70 300Hurst to the "first" pacific nationals in vegas - middle of august !!! I had the AC cranked to max and temp gauge was reading 225-230F running down the Interstate at 75mph. No detonation, no pinging, no coolant pushing out the rad/rad cap. I do remember it climbing up going up the hills, to 250F . . .but again, nothing other than higher temps, once got to top and going down, temps back down . . . But hey, it was 120F in Vegas - who has a car show on blacktop then ?????