I have a 2000 xlt ranger wit 4.0 ohv with 155000 miles. This past summer I replace the head gaskets and redid the upper half. Now all of a sudden the engine is overheating while driving than cools down to normal with in a minute .Than once I have stopped you hear coolant bubbling into the reservoir. I've flushed the cooling system, replaced the thermostat , radiator cap and checked all hoses. can someone please help me?

 

bump lol

same thing is happening to me and i have the same miles as you and the same motor. im about to do the thermostat on mine to hopefully fix it. I have a new radiator, cap & hoses and have never had head work done. replacing the decade-old thermostat i HOPE fixes it and if not, then its on to intake manifold gasket. i have no answers for you but your post discouraged me lol. i havent even had the work youve had done. it seems like replacing things on our aging cooling systems only re-directs the the issue to the next weakest link and its only a matter of time before a head takes a crap.
dunno if youll see this post, but if u do, did u ever get the issue resolved?

or did your coolant just turn brown one day?

 

I'm sorry to say my problem turned out to me a small leak in the head gasket

 

sorry to hear that, i just changed out my thermostat and the problem seems to have gone away. i may have also had air in the system from when i had in the shop (they installed a new radiator and heater valve), so getting a new t-stat and getting all the air out of the line myself i think fixed it