Temp Guage

[bigkat91]

Today I was out driving and the car was warmed up to half way between hot and cold. I sat waiting on my dad with the car idling for about 5-8 minutes and the gauge dropped to a quarter the way up. Is this normal for 3 degree weather and the heat was on.

[TrdSpeed140]

yes, using the heat draws air across what's called the heater core (like a mini radiator). The heater core has engine coolant circulating through it so when you use the heat, the heater core is losing heat to the air being drawn through it which translates to lower coolant temperatures which makes the coolant temp gauge to go down.

[karazy]

If you have it in defrost mode, it will activate the AC, which will turn on the radiator fan, which will cool it even faster.

[tarbasd]

Not speaking about the fact that the idle speed of the engine doesn't even produce too much heat, and the 3 F outside air provides a pretty significant cooling effect. So yes, it is probably normal.

[TrdSpeed140]

definitely normal

[bigkat91]

i knew that the heater would cool it a little bit but I wasn't expecting that much of a drop in coolant temp. I guess its just a 1.8L

[caddymac]

The Corolla tends to run pretty cold, which is especially noticeable in frigid weather. It has a terrible time keeping the passenger compartment warm once it gets down in the lower teens I've noticed.

I suppose some cardboard in front of the radiator would help, but I'm always afraid to forget to take it off come warmer weather.

My method to try to get the most heat is to either use the floor position (which doesn't engage the AC compressor) or to turn the defrost setting with the fan set to off (also doesn't engage the AC). When I need to defrost the windows I cycle the fan off and on as needed.

[Adama]

If it’s not needed, you can disable the a/c completely from the defrosters. Where I live, its not needed and its less wear and tear plus a little better gas mileage. The DIY is here.