heating problems

[d.brown]

i have a 98 ranger that heats great while idling, but when I start driving it starts blowing cold.. I have replaced the water pump, thermostat, radiator, and flushed it several times.. Heater core not leaking and after driving it, when I turn it off, I can hear a gurgling sound, which upon inspection, anti-freeze is going into the reservoir. Please help...... at wits end... Thanks

sorry I left this info out 3.0L, 4x4 with AC

 

[johnphufnagel]

almost the same problem

I have a 95 explorer I have heat only sometimes not very often and the temp gauge goes from 3/4 and drops down to cold.
I have flushed the cooling system 2 times I changed the thermostat 2 times and now I put a new water pump on still the same problems
I have been a mechanic for 25 years and never not been able to fix a problem.

It has nothing to do with the heater valve or the or the blend door the gauge would not be moving up and down if those 2 thing where the problem. and if the temp sender was bad and causing the erratic gauge I would have heat all the time

it is acting like there is air in the system but I am sure there isn't..
Is it possible the timing cover where the water pump impeller is could be wore down and not circulating coolant?

BTW after I turn off the engine I can here a THUMPING sound from under the hood

Please guys give me some ideas