Today, in 100+ weather, I noticed that my engine temp was getting up to 221F at highway speed with the A/C on.

Observation A) turned the A/C off temp went down to 199F.

Observation B) when I turned the heat regulator 3 notches toward HOT the engine temp went down to 209F with the A/C on.

Observation C) when the air temp got below 100F, the engine temp went to 189F at highway speed with A/C on.

I don't think that there is a problem here, just observing. 221F engine temps just make me a little nervous since my blown head gasket experience. BTW, the radiator fan is working fine.

 

On a really hot day the AC condensor is working really hard to cool down the gas so all that 'extra' heat is blowing right thru the radiator after exiting the condensor which makes the cooling system work that much harder to cool down...now with the heater turned on the heat core is acting as a secondary radiator to help cool down the water....which is good to remember when you have an actual overheating problem...alot of vehicles will experience higher coolant temps when the outside temps break into the 100's considering the cooling system is designed as minimal as possible...( why some options in clude heavy duty cooling..IE..larger radiator, and tighter fan clutch.)