I read the FAQs, archives, and current threads. No luck on this strange issue.

I have this '88 convertible that I bought four months ago. For some reason, the temp gauge runs really close to HOT before settling down to about 1/4 of the scale, like 2nd gens usually run. After it peaks, it takes only about 90 seconds to go back down again. Then it runs right where it should but I'm always concerned about how hot it seems to run on start-up.

I initially thought "bad thermostat.": I took the thermostat out, boiled it in water and compared it to the thermostats I've taken out of three my other Mazda rotary blocks. The one in the convertible actually opened the fastest of them all (though the one from my 87 Turbo II was close to the same).

Not deterred by actual evidence (and knowing about the odd bypass issue of the Mazda thermostat), I still went out and bought a new thermostat from my Mazda dealer. I tested it by immersing it in boiling water again before throwing it in the car and its performance was virtually identical to the one I was replacing, opening about 185 or so. Ho hum.

I put the new one in the car nonethess. Same problem after it was installed.

I then assumed I had an air bubble somewhere. I had just had the manifold off to replace the pulsation dampener so I figured that was it.

I've bled this car's cooling system a zillion times. I've run in maybe 700 miles on it since I replaced the thermostat. It has had quite a number of heat-cold cycles on it now. When I open up the highest cap, there is no air. Hasn't had air up there in three months. I've bled all the other oulets too (air screw on top of radiator, radiator cap, etc).

Coolant never boils. Iit doesn't seem to use any coolant in the overflow bottle, which has a rock stable level when cold.

The car is old--180,000 miles on the chassis. This is at least the second engine and I don't know if the radiator was ever replaced. However, if it was just junk in the radiator system or restricted cooling capacity, the problem of high temps would never go back down like it does.

Is there any other valve in the cooling system that could be opening later than I'd like?

Or should I just ignore this and chalk it up to a wierd old OEM gauge?

 

Verify it with another gauge before you assume there is a problem. Also, it could be a sticking fan clutch. This page may help:

http://www.aaroncake.net/rx-7/cooling.htm