Macrobb
Full Access Member
Minimum operating temp is 195-ish...I think the correct operating temperature is 195* I could be wrong. Motorcraft thermostat opens at 190* I know this for sure as I put my new one in a pot of water turned on the heat and it began to open at 190* and was fully open at 195* checked with infrared thermometer.
You are forgetting the glycol.I think with a 13 PSI cap your boiling temp is 220*-225*
50/50 glycol/water mix boils at 223F at atmospheric.
At 12 psi, that goes up to 259... Which is probably why the "HOT" light doesn't come on until above 250.
I do know that the fan, stock, doesn't engage until like 230F(and until recently, I would have backed off the throttle myself if I hit 220F)