F150, 2000 overheating.

Does the fan turn on when the engine reaches operating temperature? If so, the problem's most likely the water pump and possibly the cooling system might need to be flushed.

Try bleeding air from system like this. Remove cap from overflow tank add antifreeze to full mark leave cap off and start vehicle and let idle you may notice level in tank start to rise this is normal once thermostat starts to open level in tank will drop add more antifreeze to full mark then put cap back on. If it still overheats after this or if antifreeze freeze overflows out of overflow tank you have a serious problem like maybe bad head gasket or water pump.

I'll check. I flushed the cooling system. I can't tell if the water pump is working. It is odd that the temperature will drop so quickly when you turn the truck off.

Did a pressure test. It drops pressure but no clue where it is going. No leaks underneath, no exhaust evidence, no smoke. The top large radiator hose does not have pressure. I replaced the thermostat. Didn't help. Still will ride perfectly for about 5 miles, then temp spikes. Turn off engine for 2 minutes and it goes down to normal. Run another 4 miles and it starts to spike again.

Three flushes of the system and it resolved it. Thanks for the help yall!