91 ford explorer overheating?

Question

one day it just started overheating. Now the weird thing is, i can drive it around the block and it will heat up dramatically, but if i park it and it run, then it will cool down to normal or just above normal. Then if i rev the engine to 2 and hold it, it cools down more. But once i take off and drive again, within about 50 ft, it starts to overheat again. I figured it had bad antifreeze so i replaced it and it didnt help.

Some things i notice right when u shut the engine off

-heater hoses sound like air leaks out of them on the firewall.

While the engine is running, no bubbles coming out of the reserve tank.

When i replace the fluid, there was no oil so i doubt its the head gasket.

any thoughts?

Answer 1

Change the thermostat

Answer 2

You have bad cylinder heads.  This is an all to common problem.  Usually misdiagnosed as bad head gaskets.  Yes I read your whole question and the no bubbles part.

Answer 3

many thoughts, im guessing the water pump impeller is broken from the description you give. it may be just grabing enough to spin a bit when idling but under load cant keep up. a bad thermostat could also be the problem for similar reasons when the flow is light it can deal with it but when faster its restrcting. a coolapsing heater hose , normally there is a spring inside that holds the long section round but if the spring has colapsed the center will suck closed and you overheat. the way the cooling system works is the thermostat holds back water in the radiator for a period of time to allow the air traveling through it to cool the water below 200 degree's(aprx thermostat setting) if removed the water continually travels and doesn't stay to cool so it just gets hotter and hotter.