Alright guys see if you can help me out with a problem. I get in the 7 and drive bout quarter of a mile from the house and the coolant buzzer starts, so I drive back home and fill it up then drive to work. Well it never comes back on but I get home from work and the car starts leaking coolant out the overflow tank from the small grommet at top. So today I check the level in the tank and its empty and the filler neck on the engine needs a little coolant also, so i fill the filler neck and start the car to check for leaks as at this point I didnt know where the coolant was coming from. Well donno what the problem could be, sure hope its not a bad seal, the engine has like 7k miles on it and starts easy and doesnt smoke at all. Could it be a bad cap on the ast or filler neck? I hope so please tell me something good.

Laterz
Jeremy

 

Jeremy,

A couple of things to try. Another radiator cap for the one on the engine. Also, check the line going to and from the AST to the overflow tank. There's a connection in line that might need some zip ties. Also make sure it's not kinked or the IC sitting on it. Mine did that and I thought it was down for an engine replacement soon but it was the kink line that would allow the hot coolant to go through to the over flow tank but not when it cooled off and under vacuum back to the engine.

See ya soon,

Tim

 

damn i just saw this post after i just posted mine up above, sorry i cant help you though im having even worse cooling problems.......DAMN rx7's.........hahah i still love em though considering this is my 3rd fd, and 4th rx7 total.......

 

I had problems with the breather at the top of the overflow tank, but it seemed to fix itself?

X...

 

If the ast and coolant caps are swapped it can cause that to happen. Sadly enough a mazda dealership did that to my fd when I first got it before I found this forum and charged me a **** load to replace the thermostate and a bunch of other things and left the fact that the caps were switched on a small note in the bill.

 

I had this exact thing happen to me yesterday and I immediately pulled over to find coolant leaking out under the car. After a couple hourse of letting it sit and cool I took the cap off of the main coolant resevoir on the engine and found that the rubber underneath it had basically been torn off. Could this be my problem? And if so, why would this happen?

 

veit.. how did they switch the caps? i dont remeber what a stock ast looks like but they can be interchanged?

 

Yup, the caps look different, but they are the same diameter and can be mixed up. I believe the AST cap is supposed to allow air to leak out and the filler neck cap is supposed to hold pressure, so when they are switch after the engine gets warm the coolant backs out the resevior.

 

Doesn't the AST cap have a spring on it.. that goes up when pressure(heat) builds then lets it over flow to the reserve tank... but the other cap just has a rubber thingy...

 

Hey Jeremy,
LTNS... anyway mine is doing the same thing under heat soak. This did not happen until I installed the Fluidyne radiator last fall. I am diagnosing this currently and as soon as I find out what it is I'll tell you. I do not think it is a bad coolant seal in the engine because I NEVER have white smoke that would be a telltale sign of coolant being burned. I am still on the original engine BTW... currently at 109K =). Because of this, I was actually suspecting the thermostat being in need of a replace. I still suspect it but it could be the pressure cap on the polished AST I installed a couple years ago, which happens to be a STANT unit...
I may get another cap to try before I go and replace the thermostat.
Hey man next time you install a new engine call me.. I would have *gladly* helped. I wanted the rebuild experience for when I do my engine LOL.
I didn't know you were replacing it until you actually had finished!

I gotta go to a dyno meet sometime soon, been so busy since last year I have had no time really. Do the guys still meet up at the Dyno in Marietta?

-Dane

 

YES.



PureMdMa----can be simple or complicated. Just start with the things "Tim Benton" mentioned. Along with check coolant lines and like "EVERYONE" Mentioned, check the CAPS.

 

Jeremy,
Developed the same prob last week. Glad and sad I'm not alone with this pain. The problem started after I replaced the top filler cap(top of engine). I noticed that the rubber seal in the top cap had ruptured and coolant was getting out under the cap. The coolant was running down over the front of the engine from under the top cap. I get the correct cap from Mazda, no spring - just a rubber seal. Test run gets the temp up (110) so I check the fluid. I put about a pint in the top and fill the overflow tank. Next test run, the 7 runs hot and the low fluid alarm lights up! I stop and let cool, figure I lost about a quart on the ground after I stopped. Here's the part that got me, after it cooled it took almost a gallon of coolant! No way I lost a gallon either when I was moving or after I stopped. I had just filled it 5 minutes earlier which consisted of about a pint. The worst thoughts mentioned in other posts were coming to mind. No sign of coolant in the oil or anywhere else and I have the correct AST cap(with spring). The local shop thinks I might have an air pocket in the cooling system and needs a burp! He said its pretty common in Hondas and would explain how the system looked full but a took a gallon 5 minutes later.
When the rains stop, I'll burp the beast and let you kow what I find out.
G

 

so the cap with the spring doesnt go on the filler neck. i eliminated my AST when i was simplifying my turbo system and accidentally misplaced my foot and broke my ASTs nipple off. i just looked under my filler neck cap and it has the spring on it.

 

"IF" you eliminated the AST the pressure (spring) cap goes on the filler neck. "AS" long as you have a hose on top like most fillter necks so it can bleed the air over to the overflow

 

damnit, thats what i was afraid of. ill have to check out my setup considering i did it forever ago and i just keep adding coolant to it so i can drive it around town.
its just ironic that it started overheating and eatin coolant within a week after i got it back on the road from turbo simplification and elimination of the AST.

 

Oh another thing make sure you get your radiator cap from Mazda. The same **** happened to me I went and bought one from my local autoparts and nothing. My builder also replaced it and nothing. It wasn't until I forked out the $24 (yes for a stupid cap) that it fixed the problem.

For me next time: thermosensor, thermostat, radiator cap are all coming from mazda. Generic aftermarket replacements are well generic.

 

PureMdMa

Quick question for you, was your leak coming from the top left of the rad ? (if your looking at the rad from the front)

because i have a leak here too .


thank you


shaQ

 

How it's supposed to work:
Think of the engine as a coolant pump to and from the overflow bottle. When the engine warms up the coolant expands and forces its' way through the overflow tube into the overflow bottle. When the engine cools down it creates a vacuum, which sucks coolant back from the overflow bottle.

This works fine until one of your coolant caps develops a vacuum leak at the rubber seal. Then all that happens is some percentage of the coolant in the engine is pumped into the overflow bottle and remains there, leaving the engine a little low. This allows the pressure to drop after shutdown (because air is compressible), which in turn allows the coolant to boil after shutdown. The metal in the engine holds a lot of heat when the engine is running, and this is ok as long as there is coolant flow to carry it away. Once the flow stops, the coolant will heat up more than normal, and if the pressure is low enough, it will boil.

The classic event run is you notice the engine coolant level is way down (checking when cold, of course) when you look in the water pump (engine) fill tube. You pour in more water. It gets pumped into the overflow bottle (to stay as you have a vacuum leak and can't get it back to the engine). You are now nervous, and check the level in the engine every day (morning when the car is cold), and fill it. Soon (two to three days) the overflow bottle is full to the top and leaks out where the filler tube (removeable) joins the bottle. You see the puddle and panic.

It happened to me. Solution - replace both caps (they were old - one with spring goes on the AST, if AST has been removed, the engine cap must have a spring), replace all small coolant hoses to/from overflow bottle (they are not designed for pressure use as there is no pressure in this part of the system, so they are thin and can be collapsed under suction - stopping the coolant from returning to the engine. I replaced them with suitable pressure coolant hose routed so it would not kink (it's thicker so care must be taken when routing it - it will not bend as well). I also replaced the AST with a metal one - the stock unit is "designed to trash the engine" - it can split and leak out your coolant without giving any warning. I also ensured the lines to and from the AST were pressure type (thick) and routed so they would not kink.

Hope this gives you enough info. to solve your problem.

 

i had the same problem. i replaced my top radiator hose with a steel flex hose from summit, now it never gets hot, leaks coolant, or the stupid buzzer never goes off. btw, i have a koyo radiator.

 

Jeremy,
Got the correct caps and still had the problem, stated in above post. Took the advice of my local shop and burped the coolant system by parking on the steepest grade I could find(approx 30 drgrees) and removing the top cap! I lost some fluid and soon as I popped the cap, maybe a pint. Then we turned the car around and repeated process. Results, a one hour test run at 89-91 temp. The test run was at night so the air temp was cooler that normal. That fact that I was able to cruise for almost an hour without problems tells me the problem is fixed. The only change I made was to burp the coolant system, a cheap fix! Hope this helps some one else.
G

 

i had the same problem. David's right about the boiling and the pressure when the car stops therefore so does the coolant flow creating more heat. Well, what I did about 1 week ago was change my thermostat. And believe it or not the guy i bought my FD from put stopleak in the radiator and there was a solid chunk of it in between the thermostat spring. So i replaced it and no light came on. Then i drove hard on the freeway for about 5 minutes to my girlfriends school to take her out for lunch. After we got out of taco bell to eat my gf noticed about a quart of coolant on the ground. I looked under the car and it was from the brether hole in the overflow tank. I then went home and let it kool then i put about 3 times as much as what leaked. So i guess i had an air pocket. So then i drove my car around for about 15 minutes with my blower on hot all the way. Then I went home and filled it up a little more. I just finished doing all of this abotu 3 days ago, but I have not encountered any splurges or that damn buzzer noise yet. Hehe notice the word "yet"

 

I had to replace the stock filler neck cap, because the rubber had basically fallen off, and I replaced it with a 13lb autozone cap WITH a spring.... and i still have the leaky coolant. My coolant overflow tank is above the full line so I'm guessing there isnt a crack in it. Do you think the new 13lb cap WITH a spring is my problem? or could it still be the coolant lines running into and out of the overflow tank?

I'm guessing I will need to get the correct Mazda cap.

 

Yes. Do that. And just for clarification, people often refer to the filler cap as the one on the passanger side that does not have the spring relief valve. The cap on the AST is the pressure relief cap and has the spring.

The other point which needs to be made clear is if you do an AST elimination, you *must* replace the neck assembly off the filler cap with one from a second gen RX-7. This assembly has the correct fitting for a pressure relief cap and a nipple to hook to the overflow bottle.

 

Using a pressure relief cap on the filler neck should not cause problems; the pressure relief feature will simply not be used (assuming you have not eliminated AST and
modified your filler neck).

On the other hand, using a non-pressure relief cap on the AST will cause problems, as your system will not hold pressure; coolant is free to exit to the overflow bottle.

In other words, switching the caps will produce an unpressurized system and overheating.

What I don't understand, however, is how coolant is supposed to return to the system from the overflow. If pressure drops in the system below the cap's rating, the spring-loaded cap effectively seals off the overflow line, right? How is the coolant then returned from the bottle?

 

Aah, in answer to my own question in the previous post, apparently the pressure-relief cap has a one-way check valve that allows fluid to return. Makes sense now...