1999 Expedition over heating

[Off the wall]

Hi all new to the fourm,

Here is the problem that I'm having with my 1999 Expedition maybe someone has had the same problem.

I can be driving, heat will be hot then it will turn cold and it will over heat. Can shut off for 1 minute and then it will be fine. It can happen on freeway or city driving. Doesn't happen all the time, just sometimes or the heat will be hot then it will go cold but not over heat. Never flags a check engine light. Can fill expansion tank with coolant one day; get up next morning and expainsion tank will be empty, but no coolant on ground. No coolant coming out of tail pipe. No exhaust in coolant.
Parts that I have replaced:
pressure tested cooling system; no leaks detected.
waterpump
thermostat
clutch fan
expansion tank cap
removed radiator flushed and power washed

Does anyone have an idea?

Thanks
Mike

 

[Makdaddy]

Sounds like the Heater core may be going south