1992 F150 here with the 300 CID inline 6.
OK, I changed out the NAPA rebuilt water pump I put in 4 years ago. Front bearing was going out and I replaced it with an Advanced Auto new unit.
I now have gurgling noise coming from behind the dash. Obviously I have air in the system. I had the temp **** to full hot position when I filled the system.
Kept it full as the motor was running. I had the proper level in the overflow tank. I've driven it every day including a 3 hr round trip yesterday. I would have thought any air would have been purged out by now with all the heat/cooling cycles, yet the overflow tank never drops. Truck runs at it's normal temperature and never gets hot. Just a bunch of gurgling especially upon a cold startup. Unless I have missed it, I don't see a high point cooling system vent to purge any air. Funny I didn't have this when I replaced the water pump 4 years ago. Any thoughts? Thanks.

 

this is normal if the heater hoses have been replaced and not hooked up properly. it happens when the input coolant is put on the top side of the heater core instead of the lower side.
when input is put to the lower side it fills the core pushing any air out. if the input is connected to the top side of the heater core, the coolant can "fall through" it leaving air pockets.

this is not a major concern, it will eventually completely fill the core and bleed the air out

 

Burp your radiator, I run the truck, with the radiator cap off, softly squeeze the upper radiator hose. The level in the radiator should rise then drop, and keep adding coolant until air bubbles (burps) stop. Could also be a sign of a clogging heater core.