Have a '97 F-150 just replaced the thermostat (twice) and have flushed the system 3 times and replaced with all new "green" coolant. I am still having trouble with spiking once the system has cooled. I have been told the coolant needs to go in under pressure because of the pressurized system. Anyone know how to get an airlock out of this type of system.

 

you can normally run the motor for a few minutes untill the thermostat opens and circulates the water. the air goes to the top of the radiator. shut off motor and let it cool, open the radiator and makeup tank and top off. do it a couple times if needed. that should get the thing full. run the heater to purge the heater core also.

 

I found two plugs on the front-top of the throttle body that, once pulled, kept coolant in. These would probably be just about the top most part of the system.

But I've drained my '99 4.6 and refilled it without any problems - no air locks. With the water pump working, and the thermostat open, I would just keep the holding tank filled to the line and let it air itself out. I don't think our engines are known to be prone to keeping air pockets in areas that really need coolant for any length of time.