Okay so if I am sitting in traffic, my coolant temp will go way up to beyond 3/4 hot, but the other night rambling down the highway, it was abit of a chilly night ( maybe mid 50s ) I tried using the heat at about 90 kph and the temp gauge went from about 2/4 down to less that 1/4 and the heat I was getting was unnacceptably weak, even on full blast with the temp on full hot it still felt pretty cool.
The A/C definitely was not on, and it seemed that when I turned off the heat the temp would come up a little more. I suppose I should be checking for proper operation of the control valve on the heater hoses.
Any other suggestions?
Failing thermostat maybe?
I had one that would do that. That one was the coolant level was low.
Failing thermostat maybe?
X2 Sounds like it's stuck open.
Yup have exactly that on another car here right now that's in need of a new thermostat... Thermostat all the way!