2017 Peterbilt 579 Heat not properly working

You need to get everything drained. Disconnect all the hoses from the cab-related stuff. Disconnect what coolant hoses you can from the engine and radiator. Remove the coolant filter. Then, take a garden hose and start flushing every coolant passage you can find. Get everything as cleaned out as you can and start over. I’d go so far as to get a new thermostat, as it’s probably plugged up, too. That’ll allow another place to blast water through the engine. Again, those restrictors and valves need pulled out and looked at. You just have to start over.

 

If you got to pull t all apart
I would put a box of Cascade in the radiator on your way home.

 

Yes the Cascade dish washing detergent. Don' t use the liquid !!!

 

Sure won't
But will clean out your system

 

I had a car that acted like that. Turned out to be a thermostat.