hi all

going through the coolant loss drama

did a big search of the archives and cut and pasted up a few pages to help me find the problem

so far have tracked it to the ast pressure cap. it vents coolant to the overflow bottle when engine is hot, (seems to be about 250ml/half a pint every engine cycle, is this normal???) but doesn't suck it back when engine is cold, so eventually the collant buzzer goes off

when engine has fully cooled there is a definite vacuum in the coolant system.

you can tell because if you carefully loosen the filler and ast caps but don't removbe them they are held down by the internal vacuum, you might hear a small leak as air is sucked past the loosened filler cap

when there is a vacuum like that the small negative pressure valve at the base of the ast cap, (built into the postive pressure valve that you can push with your fingers), should be sucked open and draw the expelled coolant back

my -ve pressure valve was gummed closed. cleaning it and cycling the engine again with a remote overflow tank above the car worked for testing but connecting the overflow line back to the ast hasn't worked for driving around

have ordered a new cap from the dealer, will post back to this thread as i get more info

eric e

a big help in testing it all out and working out what is happening has been using a 6 foot length of soft flexible clear hose and putting it on the plastic overflow pipe of the ast housing instead of the black rubber oem line to the overflow tank

that way i have been able to watch the coolant leaving but not returning to the system

 

here's a photo of the test rig

 

Sorry to be the one that delivers the bad news but it sounds like a bad o-ring.

I was in denial for a while: https://www.rx7club.com/3rd-generation-specific-1993-2002-16/coolant-overflow-troubles-searched-extensively-422656/

I wish you the best of luck. Try the block seal, it worked for me, but my problem is returning, i think with another treatment of block seal and it would seal up completely. I'm done patching it though, I found a good deal on a new engine.

 

No other problems have come up? No smoke? Weird smells? etc.....?

 

Last time I had that problem, I ended up w/ a rebuild!

 

Your motor is fine, check and / or replace the hose from ast to the overflow tank, it's cloged or has a hole in it. The smallest of pin holes will not allow the coolant to be drawn back in to the cooling system. You might want to replace the oem ast with an aftermarket aluminum one, the oem ones are known split and dump your coolant.

Please post back and let us know when it's fixed.

 

I'm in the same boat as you. However when my problem started I did not have an AST, so I installed one hoping to solve the problem. So far I have the same thing happening. I've replaced all of the hoses that run to and from the AST with no luck. I am going to replace all of the caps (radiator, therm. housing filler cap, and AST cap) this weekend and see if that does anything. Please keep us up to date with what you find out and I'll let you know if I make any progress. Most of the people on here are quick to say that you need a new engine.

There is suction inside of the system when I try to remove a cap after cool down as well. However sometimes the system manages to suck coolant back in and completely fill itself up, but once it loses a little it doesn't do it anymore.

Personally my car has NO smoke at startup and there are no bubbles in the coolant when I run the car with the cap off. So that leads me to believe that my coolant seals are not bad, and the problem is with a bad seal somewhere else in the system.

Good luck, and keep us posted,
-Charlie

 

Agree with the above - your motor is probably just fine. A noticeable vacuum means coolant is not being drawn back. The AST cap (spring cap with pressure-relief spring and coolant return check valve in middle) or the line to the overflow (or the nipple on the overflow tank, itself) is plugged. The FILL cap should be a plain cap with no pressure-release spring.

 

nope look at the color of the AST... it's BLACK; no need to change it "yet". once it starts changing colors to a greenish black then it's time to replace with an aftermarket..

 

update on the lost coolant

i've used some of that pink hose to bypass the overflow line and run directly from the ast overflow pipe straight to the overflow tank, going down the dipstick hole

seems to have sucked all it needed back once but not the other time i've used the car

will need more testing

seems very important that you don't rush the check and allow the car to fully cool down

no other symptoms of a blown O-ring; no champagne bubbles, nothing more than the usual condensation burn off at startups, no excessive oil in coolant system, (the smell check i'm not so sure as i don't have much experiance with rotaries and the exhaust always stinks of unburnt gasolene to me)

what i would like to know from owners with problem free cars is how much coolant is pushed out in a simple "start and run to cooling fan" test. if the whole system is designed to only cope with half a cup of coolant being pushed out but i'm getting from half a pint to a pint then perhaps it is a blown o-ring pressurising the coolant but not letting much coolant into the combusion chambers as it's still so small???

to do a test like that you'd want to swap a length of clear hose for the black rubber overflow line and drop the other end into a clear bottle

car isn't my daily driver so i'll do lots of tests to work out what exactly is going on

have attached a pic of the ast cap with -ve release valve pulled open. was gummed up on mine and i'm hoping cleaning it out and getting it opening again will fix my problem

 

I think you've got it!!! That cap would do it.

 

Any updates? Did messing with the cap fix the problem?

Thanks,
-Charlie

 

yeah good luck on the fix
hopefully it aint a rebuild for sure