Looks like you fixed it. Good job.

 

So did you put the cap back on and then drive it some to make sure its fixed? Hopefully you can move on to the next item on the list. LOL

 

You're a prophet. Drove it to the gas station today - about 3 mi.

It overheated.

Now what? What should I focus on? It ran at idle for 15 min. and never got near half on the temp. gauge.

Drive it two miles and it overheats. What does that indicate?

 

I feel like you pressure tested it, it leaked from 15 psi to 8 psi pretty quickly, but there was no repair or definitive cause diagnosed for that? Am I correct?

 

When the gauge indicates that the engine is overheating, do you hear the coolant boiling in the radiator or overflow tank? Any external coolant loss?

Did you confirm that the air was out of the system and that you had good heat?

 

I can hear the devil himself inside the radiator.

When I turned it off, once I got home, I could hear
the pressure being released.

I was not able to see any fluid leaking in the engine
compartment, and there was no fluid on the ground
under the vehicle.

One interesting thing, if I kept the car in 2nd or 3rd
and didn't exceed 30 mi. an hour the car wouldn't
'max' overheat. I drove it home that way. As long as
I kept in 2nd or 3rd and under 30 the temperature
stayed under control..

Does that indicate anything?

 

Is the car smoking or smelling sweet?
All that fluid must be going somewhere, and if you can't see it, there is only one way: the engine.
Unfortunately, only one cure, a rebuild.

 

That's odd that at higher rpm driving in lower gears the engine wouldn't overheat as much as it would if you were at a lower rpm in 5th gear. Either way, I feel as though you have a bad coolant seal near the exhaust port or a corroded seal channel in the housing near the exhaust port. There's no reason the engine should be overheating when driving if the cooling system is working properly. And running it hot so many times has likely caused further damage unfortunately.

Is the engine hard to start after it sits and is there any excessive white smoke from the exhaust? Just spit balling for the suspected coolant loss.

When you flushed the coolant and replaced the thermostat, did any chunks of corrosion come out in the coolant? Was the coolant rusty brown?

 

No smoking, no sweet smell.

When I let it cool and remove the cap there is coolant in the radiator throat - it was still 'full' . It doesn't appear that any fluid was lost; even though it was overheating.

 

Car fires right up after shutdown. No white smoke, no odd noises. It doesn't see to have much 'umph' but it is just 1.1.

No rusty color or chunks of anything in the coolant when I replaced the thermostat.

 

If thermostat is OK and you have no loss, the water pump could be dead.

 

Could it be a belt loose enough that it only works at higher rpm ? This thread came down to loose belts...he could spin the water pump pulley by hand when the engine was not running.

https://www.rx7club.com/new-member-r...oning-1115056/

 

So just to set a baseline, are these items correct -

*Car is not losing coolant? (Earlier we thought the car was losing a gallon of coolant every time you ran it.)
*Is the fan spinning and moving air? (This would also indicate the water pump is spinning.)

IDK. Just for fun look up at the radiator through the air inlet (the car's mouth) and make sure the radiator fins aren't smooshed flat or blocked with grime, trash or rats nests. Long shot but since you're trying to rule things out....

 

I wouldn't be surprised if the impeller came off the pump. You could take out the thermostat and run it. If it still overheats, the next thing is the pump, if you're sure the radiator flows.