I have noticed that my coolant temp (the DIC reading) reads higher when I turn on the heater in the car.
I've always thought turning on the heater helps "lower" the coolant temp, not "raise" it....

Not that I have overheating problem with my car, I was just curious if that's normal in HHR?

I have ZZP tune and fan kicks in at 194F and yes the fan also kicks in when the AC compressor is on as well.

Without AC: 190-194 cruising on freeway
with AC: seems to be no changes (about 194 cruising on freeway)
with heater on (AC compressor is turned off): 194-198

when turbo boost kicks in, it seems to raise the coolant temp rather rapidly.... I've seen it 200+ (205/207 is the highest ive seen)

and yes, I have checked to coolant level, parked the car with front end higher over night after coming home from work and it checked out
ok next moring, several times.

Any thoughts? or nothing to worry about?

Thank you in advance for any input, as always.

 

Are you sure the compressor is off? In recirc, defog, or defrost, the compressor runs.

 

How old it the coolant? Recommended to change it every 5 years, going over that can noticeably change cooling performance.

 

Yes Dexcool, change it every 5 years, with 50/50 mix Dexcool and if you haven’t changed the thermostat, a new AC Delco 131-158, is a must!

 

 

I very rarely use my heater because of the mild temps around here. But, because of our unusually cold weather lately I used the heater yesterday and was watching the coolant temps.
30 mile round trip that I've done many times.
Heater off. Temps are normally a steady 185-187 while moving.
Heater on yesterday. It was showing 189-192 while moving.

Guess it does raise the coolant temp. Why? I don't know and I'm not really concerned with a 4 or 5 degree increase.

My suggestion is don't watch the temp reading so closely. You'll fry your brain trying to figure it out.

 

 

I watch everything all the time. The coolant temp definitely goes up about 5 degrees with the heater on. I suspect the flow of coolant through the system is slower since the volume of plumbing is greater when the heat exchanger is involved. Lingering longer in the block warms it a little more than usual. ?
I probably put it on defrost for a few minutes in cold weather (or zero/frigid like now) so maybe that's what it is.

 

I believe the water flow is constant - the cabin temp is controlled by the flaps and fan in the HVAC system.

 

Yeah, this is an HHR here, no fancy valves or passages like on the German cars. After first seeing this post I tested mine too and sure enough it does run hotter at first with heat on, but then evens out. Who knows why!