1996 b4000 coolant/temp issues?

[North Idaho 5.oh]

Ok, so this is a 1996 Mazda b4000 that I just recently purchased from the original owner (yes it’s absolutely mint) and it had a coolant leak from the right side of the timing cover (as you’re looking at the engine) down by the motor mount.
It does not have oil in the coolant, or vise versa.
I just went through and re-sealed the timing cover, front main seal, water pump, thermostat, lower intake gasket, upper plenum o-rings, valve cover gaskets and all associated gaskets and o-rings….
Now the issue is, I started it up to burp/bleed the system, and it’s not building pressure and the temp gage is going up maybe 1/4 way up and then going straight back to the C… Heat is on and it’s hot, took it for a drive and it’s the same thing.
Maybe I’m over thinking it or maybe it needs to be bled better? Any input would be great!
Oh, it has an aftermarket radiator cap (with the red lever) if that’s a possibility of an issue….?

 

[SenorNoob]

I'd suspect cap unless you have another leak. And getting the air out completely requires getting it almost full. (I "milk" the upper radiator hose with the cap off. You can see air bubbles.) Make sure you have something in the expansion tank. Then drive it till you have heat. When it cools it'll pull coolant from the expansion tank. Assuming of course that you don't have any leaks and a good cap.

You can usually find a parts store with a loaner tool for testing cap and the whole system. Looks like this.

 

[North Idaho 5.oh]

Ok, I’ll try the radiator cap. You’re the second person to mention that… I just finished the re-seal today so now it’s the fine tuning.

 

[North Idaho 5.oh]

And come to think of it, I believe I have one of those coolant pressure testers…. Just have to dig it out lol

 

[gaz]

@North Idaho 5.oh ,

I would not drive this until the cooling system is sorted out and known to be in perfect working condition and order.

Radiator, hoses, water pump, thermostat, heater core, water temp sender, engine temp sender, fan/clutch and the radiator cap.

If I had to replace the ENTIRE cooling system, that is way better, far cheaper and a ton less effort than losing the engine to it.

While the radiator cap is cheap and could be the culprit, I feel thermostat failure, stuck open.

 

[rusty ol ranger]

Its probably the cap but i had a thermostat fail on my 77 F250 once and cause something similar