Tried vacuum. Raised front end high. no matter what I cannot get the air pocket out of my cooling system. 97 F-150 4wd, 4.6 liter. All ideas accepted. Even the crazier ones! Oh and this happened after a thermostat replacement. Heater core not blocked, I have heat sometimes. Temp gauge spikes for a second or two every now and then. Engine isn't running hot. Pretty certain there is no blown head gasket.

 

Got to ask if you have taken the water cap off and just let the truck idle?
You can run the truck without the water cap for a little while as most hard air bubbles will then come out. (Just remember to take water with you on a short drive)
Dodge had an engine that they invented a vacuum pump system to put water in and take water out even with two bleeders for air. Go figure what that engineer was thinking.

 

Air pockets in a sealed system with an expansion tank don't happen. The air is forced out during circulation. What is most likely happening is you have a thermostat that is sticking closed and then opening past its set point. You are not the first to ever report these same symptoms. The issue always comes from using a non OEM thermostat. The required Motorcraft thermostat has the right size bypass and bleed holes in the base and its part number 7L3Z-8575-D and carried by every dealer nationwide.

 

Yes I've let it idle for over an hour with the cap off. Still have a bubble. Its a PITA, And I need to be able to let the wife drive this truck and don't want her either cold or stranded.

 

I used a large funnel that sealed well into the opening in the coolant reservoir. I filled it about 2/3 of the way to the top. I ran the motor for about thirty minutes allowing the thermostat to cycle several times. Large amounts of air was replaced with coolant. It seems to have done the trick. I'll know more tomorrow. I have a short trip that should prove if its working correctly now.