hey guys i had another thread in which many of you guys gave very good responses. the truck stays cold a while when running,then once its hot it gets really hot, the temp needle goes far enough to the right that the red engine light comes on, but after several minutes it will cool all the way down. the motor had recently been apart for upgrades. so hoping i would find something wrong i tore it back down and everything is in order. i just replaced the radiator cap with a nice one and i keep hearing that an air lock is the problem. i have no heat either. ok so today i went out started the truck cold with the cap off and let it run till it got hot, with the cap off the heat started working again, and good too. every now and then some stuff would come out the radiator, but not alot. the level would fluctuate in the radiator. but when i would rev it to like 2000 it would go down and then on the way down to idle more fluid would come out. and my headt was still working. so i filled up the overflow tank full. and went for a drive. to my disappointment , the heat soon went cold again and the temp went up again. not as high but high. and when i opened the hood the overflow tank was bone dry......
what did i do wrong???

 

What type of thermostat was installed? Stant, Motorcraft?

 

Stant 195 degree i believe

 

Some folks have mentioned loosening one of the heater hoses to allow air to escape when filling the cooling system. Your symptoms also lead me to believe you have a large air pocket someplace.

 

That happened to me before, same engine too. My truck ran low on coolant due to a pinhole leak I couldn't find. I ran the engine with the radiator cap off for several minutes and filled the radiator slowly until it was full. I had a big air pocket somewhere in the system and had to bleed it out.