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If you have just replaced the coolant, with the radiator cap off start the engine and turn the heat on full blast. Let the truck run at idle for a few minutes, keeping an eye on the level in the radiator. If it drops more than a couple of inches, add a little while running. Do not rev the enigine, as this will usually cause the coolant to spew out of the filler neck on the radiator. You will need to allow the truck to fully come up to operating temperature to be sure that the thermostat has opened. Once this has occurred, check the level in the radiator. if the radiator is full, replace the cap and add to the overflow bottle as necessary. I usually drive the truck around a little bit at this point to allow any possible bubbles to move around. You want to do this with the heat on, that way the heater valve is open and there is coolant flowing through the heater core. After you have driven a while, park your truck and allow it to cool long enough to safely open the radiator cap. Once you have opened it, top off the fluid as needed, and add any to the overflow tank.
If your using a Motorcraft thermostat, or one like it, that has a air bleed valve built in it'll REALLY help in burping the system.
Also parking with the front end up hill, or raised, while idling the engine helps, as it puts the radiator at the cooling systems high point, so air wants to migrate there.
After refilling my system, with the front end raised, I "milk" the lower radiator hose, to get a pretty good burp out of it, before the first start up.
As 643NRK said, you'll want to idle the engine long enough for it to completely warm up & have the thermostat open, as that'll help get any latent air to migrate to the radiator, so it can burp.
Leave it parked with the front end up hill & the radiator cap on & let it completely cool, just be sure you have the overflow tank properly topped up & keep it that way, as it'll burp itself & draw in more coolant as needed after it cools.
Just keep a check on the recovery tank level for a few days & when it's level doesn't drop anymore, it's burped enough to have topped itself off autoatically.
More thoughts for consideration.
Let us know how it goes.
If you are burping the heater core, it easier with a flushing tee. Otherwise, it gets messy. There is likely air in the heater supply line that can be allowed to escape by loosening the clamps on the core, sliding the hose barely off the end of the heater core tube, and letting the air out. Replace the hose, tighten the clamp, and check for hot heater core lines.
Both of the heater core hoses should be hot to the touch when the engine is running. If not, you have entrapped air or a blocked heater core.
tom