I have an 87 TII and I had my engine rebuilt about 5000 miles ago and have been trying to trace down an overheating problem since I got it back. I have replaced and checked everything I can think of thins is what I have done so far:

new water pump
new radiator camps
new koyo radiator
new mazda thermostat
new perma cool finger choper fan
flushed and bled it a few times
auto meter manual temp gauge

I just recently put in the manual temp gauge, so before that I could tell it was over heating because the stock gauge would rise to over half way when I was at idle for a while or when I was in stop and go trafic. but as soon as I got on the highway it would drop down to 1/4 as it should so I always assumed that the stock gauge was correct and not just giving me random readings.

Now that I have the manual gauge installed I am getting weird readings that show that the engine is running way to cold. Most of the time it won't go over 130, which is where the readings start. But everyonce in a while it will go up to about 160 to 170 and not move even as I go through stop and go traffic and the stock gauge goes up. I am not sure if the manual gauge is broken, which I don't really see how I mean there is not much to it. Or maybe I mounted it in a bad place, ( I put a T in the radiator hose that leaves the back housing and connects to the fire wall, see pic below ).

Any advice?

 

Is it mounted after the thermostat?

If so, your thermostat could be stuck shut, and not flowing the water it needs to properly read the temperature.

 

That is a bad location. It might work just fine IF you turn the heater on. Lever to the full hot setting. You have no flow thru that line if the heater is turned off. Not the fan but the setting has to be to the full hot so you get full flow thru that line.

I'd say it would be a faily accurate reading if you do it that way. Accurate enough to make a comparison with the stock unit anyway.

 

I can't beleive I didn't think of that of course it has to be on, thanks!!!!

Now i realize why it is a bad location.