Ford Repair: Mazda B4000/Ford Explorer overheating problem, blown head gasket, coolant tank

Question
Hi. My 1994 Mazda B4000 (Identical to the 1994 Ford Explorer) has been acting strange. The thermostat will climb to 3/4 hot, and will fluctuate around that area. The RPMs are running higher and causing the transmission to freak out as a result. I do not know whats wrong. The coolant is fine, but after the car is turned off, bubbles come out of the tube running from the coolant tank. Can you help me? Thanks in advance.

PS, the reason I am asking about a Mazda here in the Fords is beacsue the Mazda expert is no longer active, and Mazda B4000s are nearly identical to Ford Explorers.

Answer
These vehicles have plenty of problems with the engine thermostat, that is where I suggest you start. The coolant is most likely boiling due to a stuck thermostat.

Another alternative is a blown head gasket causing the bubbles, but if it is running ok otherwise I doubt that is the problem.

I am aware of the crossover of Mazda and Ford.