Originally Posted by 2101955
The gauge drops slowly and returns to normal slowly and heater air is cold
sorry I forgot that part about the heater getting hot.
It almost sounds like you donít have sufficient coolant in the system.
Note with the radiator cap off, as the engine is warming up, the coolant shouldnít start flowing out the top rapidly. It will slowly start to come up. Once the thermostat starts to open it will start to run out. However, if you rev up the engine it should be sucked back down and you should see it flowing rather rapidly through the radiator. Once you let off the gas it will rapidly rise back up and start to overflow.
If while revving the engine the coolant lowers to the point you can see the core tubes, your probably low on coolant. If you donít see any flow or its very slow either the core is partly obstructed or the water pump may be on its last leg.
Try this, with the engine cold, start it up, allowing it to idle with the heater set to full hot. While its warming keep checking the heater hoses that go to the fire wall to see if they start getting hot. If both hoses start getting hot, coolant is circulating through the core.
Once the truck is up to operating temperature, the upper radiator hose should start getting hot as the thermostat starts to open. Shortly thereafter the lower hose should start getting warm as well.
Note, it may take a while for the thermostat to start opening. I know my 2001 w 3.0 outside on a cool or cold day will take forever unless I constantly rev it up.
PS: it can be a PTA to purge the air after fully draining the coolant. I had to park mine on steep incline, while running it to get most of the air out. I did find you could get more of it out with a flush tee installed in one of the heater hose allowing it to burp out the tee cap. Even then the next day I still had to add some more coolant directly to the radiator.