Running warmer then normal

Does any one have an idea why my vehicle after sitting for a few days will run warmer then normal if I use the heater. To cool it down I have to turn the air conditioner on. It is backwards. I have taken my car to the dealership and two other shops and they can not figuar it out. Help

Model and make would be helpful. Try defrost mode with heat on high that usually kicks in the ac and see what happens. How many miles and radiator flush ever done?

thank you for your response. I have a 02 Mustang coupe, it has about 85,000 miles on it and yes I have flushed the radiator. When this started that was recomended. So in the process of less then six months I flashed the radiator three times. I had the sending unit changed, and the thermastat changed as well. The last time the dealership had my car they wanted to change the radiator but could not guarantee that would fix the problem. It does not leak any fluids I do keep a very close eye on them.

If its just a little warmer, not anywhere near the hot zone of the gauge, then I have a theory. The sensor that powers the gauge is well before the thermostat. The hot coolant is being diverted to the heater core where it gets much cooler. Somehow the thermostat isn’t seeing the hot coolant that the sensor is seeing so it doesn’t open as much. Less coolant through the radiator, so the sensor sees hotter coolant.

A lot of this depends on how the heater hoses are routed.

If I take my car back to the dealership I should then ask them to check the sensors to the cooling system? And can they/it be checked or just replaced?

I would look at changing the water pump.

I asked about the water pump and they said it was not leaking so it was good! I hate not knowing much about cars.

Occams razor point of view here . . . change the thermostat then watch it . . then change the radiator cap and watch it . . . then the sensor and watch it . . . look for debris or bent bodywork underneath which blocks cooling air . . . you’ve already changed the coolant and flushed the system . . . maybe a new radiator? Good luck! Rocketman

Have you checked to see if your radiator and A/C condensor coils outside in the very front to see if they are dirty or debri in them.

No I have not. I will do that this weekend! :o)

You hit on another idea, the AC radiator could be icing up, blocking airflow over the radiator. Turning on the AC will heat up the AC radiator, melting the ice and increasing flow to the radiator.