My 91 rx-7 is having a strange problem. The temp gauge stays are about half or so for a while (such as 20 miles of stop and go driving or 10 minutes idleing. Then the gauge rises quite a bit. The coolant level is fine, and the themostat seems to be opening since the upper radiator hose gets hot. If I let it go too long in the upper range, and I shut off the car, when I come back later, the upper radiator hose is sucked in, like all the air has been sucked out of the system. It does not appear to be leaking coolant. The coolant has no oil or anything like that in it. So, what the hell is going on. Any suggestions. The car has good oil pressure and no loss of power. I am stumped. Thanks guys.

 

Possibly a bad cap.

 

Sounds like coolant isn't being sucked back into the system from the overflow tank after the car cools down. There shouldn't be any air (or very little) in the system to begin with. Yeah, I guess a bad cap, or clogged overflow hose?

 

Ya i have a similar problem to this. I have the same symptoms except the part about the hose being sucked in. I changed the cap already and it still overheats. Im pretty sure the thermostat works but im gonna change it tomorrow anyway. What else could it be?

 

Air in the system, waterpump going bad, fan-clutch dying, etc. etc.....all can cause overheating.

 

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

But the original poster's problem is probably due to a clogged overflow tube, or perhaps a pinhole air leak.

 

I will check it out tomorrow. I'll try the cap and see what is up with the hose. I was afraid that something was really messed up. Thanks for the help guys. It's great to have a place where everyone loves the 7's.