I live in Michigan and it’s January so any help is very much appreciated.
I’ve replaced the thermostat yet the temp gauge and stays below C and blows cold air. I put a cardboard box in front of the radiator and the temp went up a little to C and still blew cold air.
Now the weird thing is when driving on the highway at 75 mph the other day at 13 degrees F I heard a change in sound under the dash and it started blowing warm air.
The temp gauge was still at or below C.
This lasted about 8 minutes (believe me I noticed when it started and stopped) and then went back to cold air.
Is there some mechanical device that start or opens the flow of hot or even warm water through the heater core?
Inside the cabin is dry and NO fogging up of windows.
I drive 150-240 miles to appointment for work and this is my only vehicle and it’s cold outside 
Thanks
Check the coolant level. When was the last time the coolant was changed? How long has it been like this? I am thinking air in the system.
Coolent is full inside radiator when I lift the cap and half in bottle. I had it power flushed 2 years ago. If it is air in the system what would I need to do to get it out and how did it get in there in the first place so if this is it it doesn’t happen again Thanks for the input.
With a new thermostat the engine should warm up. You installed the thermostat correctly, right?
Don’t block the radiator. It’s not necessary. The thermostat controls when the coolant flows through the radiator, and it shouldn’t until the engine reaches operating temperature.
You say the gauge stays below “C,” but is the engine getting warm? Maybe the sender for the gauge is bad, or the gauge itself.
Is there air in the cooling system? You have to make sure there are no air pockets.
Feel the hoses going to and from the heater core. When the engine is warm they should both be warm or hot, too. If not, there’s no coolant flowing through the core.
If the core is hot, then the problem is in the HVAC system under the dash. You had heat briefly, so there must be some coolant flowing through the core, at least sometimes.
Make sure there’s no air in the cooling system, and that the engine and heater core are warm, then look under the dash.
Yes thermostat was installed correctly.
Radiator was only blocked before the thermostat was replaced.
Yes engine is still getting warm
Don’t know how to check for air pockets
I’ll check the hoses to and from heater core
What is the HVAC system under the dash? If the other items are working what will I be looking for with the HVAC?
The time it did blow warm air there was a different sound under the dash when it was working. I can’t explain it well a subtle difference but after driving it for over 190k miles you pick up on those things.