Originally Posted by cmgood
The coolant temp indicator seems to fluctuate a bit. It will warm up to a directly vertical position only at a stand still or in slow traffic. If I am on the highway it will cool a notch or two and then return to vertical a while after sitting.
This could also indicate a very low temp thermostat was installed, or no thermostat is installed, or it has been disabled.
Radiator fan is controlling temp while sitting, but when you drive at higher speeds, ambient air is cooling down coolant to a lower-than-normal operating temp.
Agree with doing a new thermostat (87 C) when you do the TB service.