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97 Mazda Millenia runs hot when cold outside!

Mechanics can’t find out what’s wrong but the car doesn’t overheat when it’s hot outside & I use the AC, only when it’s cold outside and I use the heat. I’m not sure what the mechanics tried thus far but they can’t figure it out. Ideas??

It may be that the radiator fan isn’t coming on unless the air conditioning is on. This fan may need to run in cold weather to pull air through the radiator, particularly in stop and start traffic. If it doesn’t overheat in cold weather when you are doing highway driving, but only when driving in traffic, this is probably the problem.

I agree. I don’t believe the primary radiator cooling fan is operating when the heat it used.

A quick way to determine if this is what’s happening is, drive the vehicle either with the defroster turned on all the time, or turn on the air conditioning. This will force the secondary radiator cooling fan to run. And as long as you have the heat set to high, doing this won’t freeze you out of the vehicle. If when doing this the vehicle no longer overheats, it pretty much confirms the primary radiator cooling fan isn’t functioning.