I tested the coolant system with a pressure tester today. Got it from advanced auto parts, it was a pretty good kit. Don't get the pressure tester they have at auto zone, it only has one adapter and no, it is not the one for the rx7 that's for sure.

I hooked up the tester to the filler neck area and applied pressure. It went up to 13 fine and would hold at 12. Then after I let it sit for a minute or two I could tell it was going down really slowly. In about 5 minutes it had gone down to 10psi. I looked all around for leaks but I didn't find any. So I thought the worst, that coolant had gone into the chambers through the coolant seals. So I replaced the cap and started up the car. It did struggle a bit to start, but there was no steam or smoke from the exhaust and it idled fine after about 5 seconds. I am stumped. I don't know what it's doing. Unless someone has another suggestion for me to test another way I am going to take this car to a shop tomorrow and hope they can diagnose it.

Perhaps it's the radiator itself. Still wont take coolant back into the system.

 

plan B would be to put the tester on it, pump it up to like 20psi and just wait.

if it only holds 10psi for a minute or two, it should not be too hard to find, unless its something weird like the heater core

 

When the car is running and the cap is off, does it spew a lot of coolant? Not just the normal fluid expansion as it heats, but flows out. If it does, chances are you have a water seal leak. The compression of the rotors is pressurising the coolant system and forcfing fluid out the the only open hole (the radiator cap)