seevi

I was driving to the gym this morning at 6:00AM and the ambient air temperature was 28 degrees. I had the temperature set to 80 degrees to replicate the inside of a toaster when I noticed the engine coolant temperature was 205 degrees. I dialed the temperature down to 70 degrees and the coolant temperature dropped to 198. I turned the temp back up to 80 and sure enough, coolant temp went back to 205.

Anybody have similar experiences? Any thoughts?

Ragtop 99

Coolant temps will vary as the T-stat opens and closes and the fans cycle on and off. Probably just the stock fan settings cycling on and off, although I don't the stock settings convenient to check for you.

nwc6

Could it be the climate control saw enough of a negative temperature change to command the AC to come on, triggering the fans to run?

davekp78

Are you running the stock thermostat? What temp do you usually run at?

YLOFEVR

Engine temps vary with T-stat function--all commanded by ECM, not your climate control.

blue383

I agree with Ragtop 99, probably you just happened to change the setting when the fan cycled. The only effect the climate control could have would be if the engine is getting too hot and the cooling system can't keep up - then turning up the heat in the cabin could REDUCE the engine temp by removing more heat from the coolant. That would never happen in winter.

Bill Dearborn

It could happen under the right circumstances. I had the radiator freeze over in one car that had a low antifreeze concentration. It was windy and just cold enough for the radiator to get cold enough to freeze. The only way I could keep the engine from overheating was to put the heating system on full outside air and turn the heat all the way up.

Bill

seevi

I’m running a stock 187 degree thermostat. Last October I drove across country in temperatures ranging from 40 to 105 degrees and the engine ran at 198 degrees day and night at speeds from 65 MPH to 80 MPH. As for the fans, there set to come on early.

The recent cold snap that hit eastern North Carolina has giving me the opportunity to duplicate the rising temperature occurrence on three occasions. At first I thought the computers might be intuitive enough to somehow let the engine increase its internal temperature for the comfort of faster cabin heating but couldn’t figure out how. Commanding a higher cabin temperature by increasing the temperature continuously drives the coolant temperature up to 205 degrees on each occasion. Dropping the temp down to 72 degrees brings the coolant temp down to 198.

Vito.A

The coolant temp changes you see in the DIC have a lot to do with the location of the sensor.
Your heater core is a heat exchanger just like the radiator, but smaller. As you increase the inside cabin temp the climate control is opening the coolant valve letting more coolant flow through your heater core resulting in a temporary drop in coolant temp and then the thermostat reacts by closing slightly reducing the amount of coolant going through your radiator which in turn results in an overall rise in coolant temp.

I suspect if you were on the free way traveling at a constant speed you would see less effect.

seevi

All three times, curz control set at 65 MPH.

davekp78

I agree with this idea except that the heater always has full coolant flow. The temp control varies the amount of air flow passing through the heater core.
Anyway, we have an unusual thermostat arrangement in that the thermostat is very influenced by the temperature of the coolant returning from the heater. A large drop in the heater return line temperature could "fool" the thermostat into opening more than usual, resulting in a lower than usual DIC temperature reading.

dgrant3830

Same thing happened to me many years ago in a VW Scirocco that I drove forever. Coolant mixture wasn't right for the temperatures that I found myself in and sure enough, it froze up but the overheat light came on. Did the same thing, used the heater core as a radiator till I was able to warm up the real radiator, drain and refill with the proper mixture.