91 Mazda b2200 overheating

Was on a road trip and the truck started overheating, I turned on the heater and it cooled down and got me home. Replaced the thermostat, replaced the water pump, hooked up a water hose (removed the thermostat) and water flows through the system. It is fine while idling but overheats in 2 minutes of driving, sometimes the cab heater blows hot at the start and quits or does not work and then starts. No white smoke at tail pipe.

Can I have a "sometimes" block in the heater system as well as the radiator cooling stuff? A blocked radiator would overheat the engine, but what about the heating system? Everything combined has got me confused.

Lifted the front end last night and lots of air bubbled out. The truck worked great, lots of heat, started and stopped it several times, drove around the block. All worked well. THEN this morning, no heat out of the heater and overheated in 2 miles. So I am back to square one. Going to check my oil for water and then go over each hose and maybe install a bleeder valve at the high point.

Here is what I found out. Hindsight is always better, but maybe this will help someone else. The truck would overheat and I would notice that the radiator was a little low, I would fill it up and be good for another 2 months. No big deal, small leak in a hose somewhere. Now jump to today and the radiator cap was really leaking. Thought I found my coolant loss, bought a new cap and no coolant loss but now white smoke and now I have water in the oil. So, head gasket, maybe more....that's my story.

With these trucks it can be hard to get the air out of the cooling system. Put the front of the truck on jackstands and start it with the radiator cap off with the heater on. That will get the air out of the system. Trapped air can cause overheating sometimes.

What I would suggest is getting a bock checker and pumping up the water jacket and checking for small leaks. The small hoses will break and not give much of a clue as to leakage and will give the kinds of symptoms you are describing.

Swami Cuss says: If you still have the original old radiator, I see a new 2-row radiator in your future...