So, I have a 1989 rx7 FC. Stock 13b n/a. I have been having an issue with my cooling system lately. The car has never overheated. Here are the symptoms:
I lose coolant, but no visible leaks
Overflow tank is getting more and more full.
Coolant Buzzer will go off sporadically at least once a week, sometimes more.

Usually when the buzzer goes off, I just top off the radiator and it satisfies the issue but isn't the solution. I don't think I have a leak, I think as the car gets warm, the coolant expands and overflows to the overflow tank, but for some reason when it cools down it isn't drawing that fluid back into the system.

so what would be a good starting place for this issue?

Thanks for any help!

 

Maybe a new sensor.

 

The small tube that empties into the overflow tank could have a pinhole in it. I believe if this were to occur then a change in pressure within the system would pull coolant out of the system and into the overflow tank.

 

Building on what satch said; check the cap to the overflow tank cap as well. I've seen several crack with age which causes a pickup issue. It also wouldn't be a bad idea to check the condition of your radiator cap(s) as well.

 

Would a crack in the overflow cap really affect anything, because system isn't a closed system. Air is already escaping through the dump tube on the overflow tank. I am thinking there may be a tiny little pinhole or something in the hose causing it not to be able to creat the suction. Ill replace the connecting hose from the radiator neck to overflow. For the radiator caps, what psi cap should i get. Also, is there multiple caps?? I have only ever seen one in my car unless the second one is super hidden.
Thanks for all the help!

 

do a champagne test. i only know of one reason why coolant gets pushed to the overflow and you have to keep adding water...

 

Thats where u take off ur cap, run the car and look for bubbles right? I havent done that since bleeding the cooling system after i flushed it. I will try it. But the idea of a rebuild in the near future is not good. Id probably have to get rid of my 7. So hopefully its just a pin hole in the tubing or something simple!