Hey guys- Expecting the worse-

Bought a used engine, as it was cheaper this way than rebuilding, but looks like it was a risk. Prior to buying, I did a coolant pressure test of just the block. Held @ 13 lbs for a few minutes until the silicone between the front iron & WP housing block off plate failed. Engine was removed from an NA in prep for a T2 swap.

Anyway, I have it installed in the car now.

-All ducting is in place
-New coolant
-OEM clutch fan
-Aftermarket copper tank radiator, had blown out by a rad shop & pressure tested, held.
-injectors all cleaned
-New thermostat 180*
-No leaks when pumped to 13lbs w/ pressure tester.

*water pump was re-used, however, new gaskets are in place, & again, no leaks

Here's what's going on: The car comes up to operating temps (it's an 87, so 1/4 up the gauge) rather quickly- in only about 3/4 a mile of driving from a cold start. However, it doesn't stop at 1/4. It will continue up to the 3/4 mark on the temp gauge, a confirmed 220*F w/ an infared thermometer measure at the rear iron's outter surface, and 231*F at the top tank of the copper rad. The gauge sits at 3/4 no matter if I'm at a stand still or going 60 on the freeway.

Other than exhaust gases getting into the cooling system from a bad o-ring which lets combustion in, but not coolant out, I think the problem could be from:

-Thermostat not opening fully/at all
-bad water pump? Though the upper rad hose has plenty of pressure when up to operating temp..

Any help would be great- I'm prepared to pull this out again & actually open it up/rebuild this time, so if that's the case no big deal, just some $ & time wasted. But if that's avoidable, that would be great!

TL;DR: Engine slowly creeps up to a 220*F temp when measured w/ an IR thermometer at the rear iron. All shrouding/fan is in place, no leaks as tested with pressure tester, new thermostat, radiator has been blown free of clogs.

Thanks!

 

If you've verified that the cooling system is holding pressure, it sounds like the thermostat isn't opening fully, or the water pump may be bad.

Did you get the thermostat from Mazda? I was in a pinch and went to Autozone to hold me over. I asked for the 180 degree one, and their stock system was screwed up... they actually gave me a 195 one.

In any case, make sure you've got an OEM one.

 

Its not a Mazda but I did obtain it from a mazda service shop locally here. It has 180*F stamped on it, the bypass blockoff when opened, and a jiggle pin in the fsm posistion. It may be not opening fully/at all, I'll have to pull it & boild some water to see.

Waterpump is definitely a possibility, though the impeller looked fine when I had it off

 

How many times did you heat cycle the engine? It took my car 4 times after putting the koyo rad in to full bleed the air out.