Reader Question: I have a 2000 Ford F-150 Pickup. The temps around here are -20 today. This morning I set out for work, started the truck for 30 min when I got in the heater was blowing warm air.
I got 10 miles down the road and noticed the temp gauge was pegged in the hot zone, my oil pressure light and check engine light came on but my heater was still blowing hot air, I pulled over and the engine wasn’t overheating I shut the engine off and restarted the temp gauge came down within 30 seconds.
This has not happened the rest of the day. I have added more coolant. One thing I noticed now is the temperature gauge now does not come up to the 1/2 way mark. I still have heat.
The coolant in the reservoir is cold, the top radiator hose is warm not hot my hoses going to the heater core are hot and I do not feel coolant moving thru the hose. I have left it idle for an hour and seem to get no pressure when I remove the reservoir cap.
Before I added coolant, it was good for -20 below
After I added coolant, it was good for -35
It is late, I am tired, and maybe that is why I do not really understand what your question or what the problem is or if you really have a problem. I want to know how much coolant is in the radiator itself and not the overflow bottle, how much coolant did you add to the system and is there a coolant leak in the system somewhere.
-20 degrees is darn cold! Since you say, you still had hot air coming out the heater vents that is actually a good thing. That tells me you HAD enough coolant in the system to operate the heater and that there probably was some circulation of coolant.
You also said that you did not notice actual overheating taking place, no boiling over or hissing noises, etc. etc.
So, here is what I would suspect…a gauge problem, probably due to a faulty temperature sending unit or a bad connection at the sending unit on the engine. Temperature gauge goes red; you pull over and turn off the engine thus resetting the temperature sending unit.
Now, you have a very different reading than you did before and you really did not do anything to change it. The sending unit is just reading different. The sending unit is cheap and easy to replace yourself if you want to take a guess.
OR a wacky thermostat that stuck for a moment just enough to show up on the gauge. I guess that is possible, and if it has been awhile since you changed the thermostat. It would not hurt to install a new one as maintenance.
Keep me posted.