My Detroit 60 will drop engine temp to 50 idling in cold weather.

coolant mix ratio wouldn' t have anything to do with it. even straight water will run the same.

i usually drop to 170 when idling that cold. the fan don't ever come on. your heater core works just like the radiator. when it's that cold. the heater alone will cool the truck down.

i would do a ecm check. see if the ecm is reading the same as the gauge. your sympton is typically a bad thermostat. but like others have said. it could be the gauge sensor.

 

i changed both thermostats, no more cardboard, good heat

cost $85 parts and 30min labor (my labor)

 

Hi