I have a 2000 Ford F-150 XLT 4x4 with 193,000 miles. I had a no heat issue and replaced the thermostat. That wasn’t the problem. Turned out to be a blend door actuator. Then about 5-6 weeks after the thermostat and actuator replac started experiencing some coolant loss and a slight smell of coolant in the cab. First thought was a leaking heater core. Always had heat and good heat too. My thought is the overflow container spewed some coolant out from a loose cap. I filled the low coolant and tighten the cap till it clicked. Seemed to have done the trick. Then every once in awhile I’d get an overheat issue and it triggered the temperature icon dummy light on the dash and service engine soon light. Plugged in my OBD II and gave me a code (can’t remember) states the head has exceeded or high temperature warning on the heads. Clhecked for a blownn headlgasket simply by checked the oil for splotching or other signs of contamination and it looked normal. I believe now there may be an air pocket in the cooling system and tried a few techniques and it worked some suspect there is still air in there. As I still get the overheat issue. How do I get the air out fully from the system without filling the coolant under a vacuum? Also can a water pump wear internally to to point it isn’t circulating the Coolant sufficiently? Before any bearing issues because she sounds normal. I thought I also smeltt a wisp of sweetness from the exhaust but not sure. Now I’m thinking it might still be a head gasket. Want to try some coolant sealer stuff before replacing but need all air out. Is there a trick doing a coolant fill using a shop vac or something? I’d appreciate any suggestions comments or criticism please.