1990 b2200 overheating

Hey guys I need some help plz. I recently got a 1990 Mazda b2200 and the engine was supposed to been rebuilt. It runs great but it gets hot and when u check the water its low and always takes a lot to cool it back down. What could be wrong please help. Thanks.

Well, there's ONLY two choices for the coolant being low:
1. a leak, which may only show itself once pressure builds up. Common places would be bad cap, leaky radiator, bad radiator hose (don't forget the three small bypass hoses on the passenger side of the engine), bad heater hose, bad heater core, bad water pump.
2. coolant is getting into the combustion chamber (like through bad head gasket, cylinder head, a crack) and going out the tailpipe

So you need to isolate first which scenario it is. Even without a leak or a leak into the combustion chamber, a 22-year-old radiator can become so obstructed that it can't shed enough engine heat. Do you have a coolant overflow reservoir hooked up, and correctly?

It has a new thermostat and tax cap that I installed myself. When u cut the truck off it bubbles inside the over flow very baf. The over flow is all hooked up correctly. How could I tell if the head is cracked or gasket is blown without pulling it off. It doesn't seem to steam outta the exhaust.

Cylinder leakage test. Air pressure put into the cylinder through spark plug hole when piston is at TDC; air/bubbles observed in the radiator indicate path from cooling system to combustion chamber.

Thoughts are crappy radiator and heator core as said.And if the engine was when coolant was added the air bubbles inside were not bleed off would create this issue.Try cold start leave rad cap (OFF) heat on,fan high run for 15-20 minutes and yes coolant might bubble over use rags to catch then cap it.This helps remove the air unless you have issues with a rad/htr core I seriously would just go new,and not flush forever on end with same issue.Also placing some cardboard between the rad support and block air flow speeds up the heat up time in half and see if you have air pockets (bubbling) with rad cap of while it warms to normal temps.Sorry for the book just giving as much info to rule out the engine being a problem,and the easy stuff rad/htr core.

if u plan on gettin a new radiator go on ebay theres a radiator shop in Hialeah Fla where i got mine all aluminum all welded stock replacement cheaper than the crap and autozone and advance and its 2 row direct fit