overflow tank boiling over?
 

I have a strange coolant leak. The other day when I came home from work, I went outside to go check the mail. As I walked up to my car down the walkway, I noticed there was about a 1 foot puddle of coolant on the left hand (passenger side) section of my car. I was curious where it was coming from so I jacked up the car. I took the splash gaurd off, and looked around under the car. I noticed there wassn't any leaks coming from any of the main lower or upper radiator hoses, or from any of the ast hoses and such. This leak was also not coming from my radiator due to the fact I have a fluidyne radiator. Then just as I was about to give up, I looked over toward where the overflow resivoir sits. There was fluid all over the bottom of the plastic under the overflow tank it self. I took the plastic piece out of the way, and saw fluid all on the bottom of the tank, as if it leaked down from the top somewhere on it. So I lowered the car, poped the hood and looked at the overflow tank fillter neck. Nothing seemed out of the ordinary, until i noticed spashes of fluid around the engine bay. It looked like it had boiled over somewhere. The filler neck had a small crack on it right by the top cap. So I pulled the neck out of the tank, and got some tape and taped it really tight to where nothing could escape it. After that I put it back into the tank and everything looked ok, i guess...

I went to a car show last night and noticed a 1 foot puddle of coolant on the ground...very pissed off, i drove home and went to bed.

I know it's not loosing the coolant from the radiator or block, because my motor runs very cool when it leaked out. I pretty much am assuming it's coming from the over flow resivoir but I dont' know where. Also, it only leaks once the car is off and has sat for a second. What would you guys recogmend I do? Or does this sound familiar to anybody? Any help would be greatly apreciated, if i can't figure this out by the end of the day, i'm taking my car to Marvelspeed and having them fix it.

Thanks

AST cap needs to be replaced.

Ok...is there a way to test this? or is this just your gut instinct? I take it this has happened to you?

There is a way to test it, but it runs five bucks to replace it so why bother.

No, this has not happened to me but this has happened to others on this forum.

Ok, i'll try that, thanks.

Same thing has been bothering me for the last three months.At first it was tiny cooland(maybe 5-10 cc)missing setting the add cooland buzer off.Then cooland would come out from the base of the neck of the overflow tank.
After having presure tested the cooland system,inspected all hoses,having the radiator cleaned,even changed both caps,it was still the same story:after shutting the engine down,I would hear bubling noises from the overflow reservoir,and coolant coming out from the botom of its neck...It seems that it's "neck"is only attached to its main "body",n o t broken!!
Now bad news is that the cause was O-ring failure:As the O-ring got more damaged the problem got worse.
Good news is that the engine didnt overheat.Now I have to face engine repair....
Hope you'll be more lucky,with only a minor problem!!
George.

AST cap... could be. Mine was the filler neck cap.

I suggest you get a REAL MAZDA cap not the autozone/napa/aftermarket replacement cap.

The autozone cap didn't do shit for me, and I tried a couple of them (so did my builder). It wasn't until I bought one of Mazda that it fixed the problem.

I dis-agree with everyone's opinion. I think its your overflow tank. I'm fairly certain you have a crack on the bottom of the tank.

What happens is the tank develops a hairline crack. When you fill the tank up it doesnt leak. Go for a drive and the heat causes the crack to expand. When you park the hot coolant causes it to expand and it leaks. It usually takes 5 minutes or so after you park. when you fill it back up it doesnt leak cause the crack contracts again.

Its not your AST cap. Trust me your coolant system is under pressure if that was the problem you would have coolant leaking when you are driving and it would be obvously leaking around the AST (you would see white/green residue).

BTW, dont bother looking for the crack on the tank..I have my old tank and cant find it, but I know its there.

One of the things I did to hold me over until I got my new tank was by permatex seal a gasket and spray on the bottom. A better idea would be some silicon glue like "goop". Just cover the entire bottom of the overflow tank and let it dry before you drive.

I had this same problem all of a sudden one day and I noticed when I took off the filler cap that the rubber was basically gone(provided no seal). Replaced it with an Autozone cap and the problem was still there... then replaced it with a Mazda OEM one and Voila! It was fixed.

Also, There is supposed to be a hole at the base of the overflow neck. This is designed incase you put too much coolant in the tank it overflows.

When it happened to me I replaced both caps and the problem was gone. My AST was also showing a bit of coolant on top sometimes so I also got the aluminum replacement. I have had good luck with the autozone caps.

Zerobanger seems to be hitting it on the head, due to the fact that the coolant is resting on the bottom of the tank. Thanks for the input guys i'll check on it today and see if i can figure it out.

Two theories:

1) the AST cap leaking. Since the filler neck cap is not even a pressure relief cap, if it is not visibly leaking coolant it should be fine. On the other hand, if the AST cap's "pressure relief seal" is not sealing with the AST neck then coolant can escape to the overflow bottle and overfill it. I had an aftermarket cap whose seal did not fit the AST's neck correctly - it had to be "bunched" or "bent" to be inserted - it leaked, and caused the symptoms you describe).

2) you have been checking the coolant level with the engine warm. Under normal operation when the engine cools it develops enough vacuum to draw coolant back from the overflow bottle. If you are routinely checking the coolant level before the engine is completely cool you are preventing it from sucking coolant back out. Then, since the level in the filler neck looks a bit low, you add more, repeat a few times, and the overflow bottle soon overflows.

Not true necessarily. The inner pressure-relief seal is the one that is suspect, not the cap seal, which would indeed show obvious telltale signs of leakage if it was bad.

Guys,

You all mean well, but it has NOTHING to do with the AST. The AST is on the OTHER side of the car toward the battery. The puddle would be on the drivers side, not the passenger side. AND...it would leak when he is driving it as it is pressurized..as he stated it only leaks after he parks it. And again, there would be coolant smell inside the car and stains where the cap is..

The problem is the overflow tank itself.

Well yes it certainly could. When the cap leaks on the pressurized (inner) seal, coolant leaks into the overflow hose and fills the overflow bottle which IS on the passenger side and will NOT show a leak on the driver side. It typically leaks after the car is shut down, as that is when the temperature is no longer in check by virtue of circulation through the radiator, i.e. that is when the coolant is at its hottest and therefore highest pressure.

The coolant overflows from the overflow bottle well out of sight and away from the heat of the motor, so no smell and no stains at the cap.

I hate to argue with 3400+ posts, but in this case you're missing the issue.

WOW, yeah i pretty much had the exact same problem the last couple of months. My car would start overheating unless i had the parking lights on, and its wierd because when i shut the car off after a good long drive, and tried to turn it back on, sometimes my collant buzzer and light would go off, i figured it was boiling over and going into the overflow and seemed like it wasn't comming back. It would be low sometimes when i went to check the regular filler neck. Oh and i definitely had lots of gurgling, boiling after i shut the car off almost everytime. Anyways, today i went up to ray at malloy and picked up both the regular cap and ast cap and replaced them, so far its been running cooler, and better, now i just have to see if it's leaking anywhere, or if the coolant stays in, it sucks though because when i was leaving the temp gauge started climbing quick, before i replaced the caps, so hopefully, i didnt do too much damage, oh by the way guys......if the it overheats bad......what kind of damage does that do, as far as is the motor still good, although it would have to be rebuilt, or would the motor be trash and i need a completely new motor? i don't think i hurt too bad because with my parking lights on the temp was usually normal in the middle, just today it started climbing for the first time after an hour drive up there in the heat. hopefully all is well still, i hope.

I would bet the problem he is having is the coolant tank itself. I dont have experience with the issue you are talking about, but what ever the problem is I hope he solves it.




Please post back when you resolve your issue!!

Well a little update, I went home the other day after work. Parked the car in the garage, and poped the hood and let it sit, i sat there and watched it for about 30 minutes, and going in and out after that. It never leaked. I'm guessing I had the tank too full. Even after it was leaking a lot before, the tank was full, as well was the actual coolant in the car. Thanks for the help guys, i think for now it's fine. If it comes up again, i'll see if i can look for any other signs of it being something else. Thanks

^ Don't be too surprised if it happens again. :)

You did state that the coolant was on the bottom of the tank right?

Two scenerarios:

1) Your tank really is craked like zero said.
Or
2) You missed seeing the coolant coming over the top of the tank and then resting on the bottom. (this would mean that you over filled it, AST/filler neck caps crapping out on you, a small hole in your coolant system, blah, blah...)

Here is another option, which would cause a leak between the AST and the tank.

The stupid oem line going into the tank.

It is actually 3 separate hoses, with some stupid plastic connectors in between.