l own a 97 Subaru Legacy, and this is mind boggling to me. In the summer, the AC is on and the temp does not raise, but in the winter when it is cold, it raises pretty high. l have to turn the heat all the way up to bring the needle down. Someone help!

When you are running the A/C, the electric fan is on all the time. With the A/C off, the fan only runs when the engine reaches a certain temp. My Chevy is the same way.

There is a mechanical thermostat that opens & closes allowing coolant to run from the engine to the radiator & when it is very cold this thermostat may not open at all or not open fully. Sometimes u will se the temp go up & then down & then up & then down over & over again in extreme cold as the thermostat opens & closes. Depending on engine design, some thermostats allow seepage of coolant to the radiator even when closed so that the hot coolant can reach & effectively ''open'' the thermostat. Otherwise the hot coolant runs past or near the thermostat without passing through to the other side so the thermostat may open at too high a temperature & the rapid change in coolant temperature from boiling hot to ice cold (as in the dead of Winter) causes too rapid a change in engine temperature & this creates stress on the engine management systems & can cause a headgasket problem.

The cold Winter air temp is actually help cool the engine through the air intake manifold, the heater core, & the engine block, in ur case l believe it is aluminum, & of course the radiator.

Your cooling fans (radiator fans) will not come on in Winter & may run non-stop in Summer.

The only thing u might check if this bothers u is the actual mixture of coolant & water. It need to be a 50/50 mix & l recommend u use distilled water when u mix it with antifreeze. This keeps scale from building up in the coolant jacket & cylinder heads & radiator. They sell these little antifreeze/water concentration testers in most department & auto parts stores.

If this were an air-cooled engine the opposite would be true & none of the above would apply.

Good Luck!

Now that is interesting. My Escort reaches the same temperature on a frigid winter day as on a hot summer day with a/c on, & it has not varied by more than a few degrees maximum for 3 years. If u have a thermostatically controlled radiator cooling fan, the switch may be shot, or the fan itself may be dead. If the temperature is fine when u r cruising the highway in the summer, & creeps up when u r in town, that sounds like the fan is either not coming on, or is coming on really late. That is not a terribly expensive fix either way.

simply because of your a/c fan and radiator cools the air down before it gets to your motor radiator