Hi all,

I did a search on this problem before posting, and found that the most common causes for this to occur is:

1. Dodgy radiator cap - Have already tried 2 (although not genuine Mazda ones), problem still there.
2. Coolant leak - Yes, I have a very small one, but I'll get to this later
3. Failed (or failing) coolant seal o-ring - well... I hope it's not the case... It passed the "bubbling test" and I haven't had any problems with overheating.

I've found a very small coolant leak coming from the plastic upper water pump hose (seeping from under one of the bolts). It isn't losing a lot of fluid from there, but is it possible that when the engine cools down, because of the slow rate of cooling, instead of pulling the coolant from the overflow tank, it pulls air through the crack in the plastic hose?

Any suggestions will be greatly appreciated. Although I doubt it would cause any major issues, I'd really like to get this fixed before the track day next week...

Thanks in advance
- TT

 

maybe the water pump is no good?

 

It's a very tiny leak.
It's enough to suck air, but not big enough to leak coolant.
In fact, coolant probably leaked through the hole and then crusted enough to prevent further coolant to leak through.
But air still leaks by...


-Ted

 

Whats the bubble test. You turn ure car on and leave the cap off. ANd you accelerate and if it comes out the rad cap then u have a blown coolant seal. or do i have it reversed

Jason NYC

 

i would try fixing that leak first. if its not your problem then at least the leak is fixed. take off the plastic goose neck from the thermostat housing and reseal it. thats if its an S5. the only difference with the S4 is that the neck is metal i believe and it has a cap on it.

also use mazda genuine caps due to the fact that our coolant systems are so touchy that if something isnt exact it could cause a serious problem. for instance the cap could not have the bottom part that is used for overflow. or the rating of it is off and could be too high of a psi cap. off hand i dont know the actual mazda specs on those caps. sorry.

Brian

 

Thanks for the feedback, everyone.

Ted, that's exactly the theory I was going on...

Jason NYC, the bubble test that I did was leave the cap off (when the car is cold!), removed the EGI fuse and got my bro to crank the engine over, looking for any bubbles coming up out of the filler neck. If you turn the car on with the cap off, and the fluid level is approximately at the filler neck, after about 30 seconds of running, the fluid will have expanded enough from the heat to overflow from the filler neck! Well, that's what happened to me when I first attempted the "bubble test" anyway...

Brian, yes, it's a S5TII. I'll check out that leak next up, before unloading some stupid amount of cash for a radiator cap from mazda... might even take them 2 months to get it in, like everything else.

Hopefully it's not the water pump! If it was the case, I'd expect to see leaks after the car was sitting around for a while and also I haven't had any overheating issues. It's not losing any noticeable amount of fluid (apart from when I don't check the overflow bottle for a while and it pisses out all over the concrete)

Cheers,
- TT

 

Mazda radiator cap $17.00 two years ago. You will find a lot of negative experiences posted with other than OEM caps if you search. The cap came in two days after ordering from dealer.

 

thermostat

 

Fair enough about the radiator cap, I guess that's the surest way of removing all doubts. It's just that I've had nothing but negative experiences with dealing with Mazda in Melbourne...

As for the thermostat, well, I'l have to disassemble the upper goose neck to fix the leak anyway, so I might as well as have a look at it.

Cheers,
- TT

 

ted answered the questeion

no its not the thermostat... dltreezan, have you even seen a thermostat?

 

I love all the random crap that was thrown out in this thread by people who don't know...Clearly the problem is the water pump! LOL. (that's sarcasm).

If you DON'T KNOW, DON'T POST! Guesses are not acceptable.

As Ted mentioned, it's a pinhole leak. Likely in the hose that runs from the pressure cap to the overflow bottle.

 

well the same thing happened to me when my thermostat went out. Car would get warm and all the coolant would go into the overflow and not go back in. Maybe that was just my experience. I had also been driving the car for 43 hours straight.

 

ding ding ding, ted got it.
most likely a small leak in the hose, possibly check the plastic around where your overflow nipple connects to the cooling system. 80s mazda plastic is very brittle

 

hmm, i was thinking faulty cap but you guys seem to have it under control..



that was sarcasm btw!

all we can do here is post educated guesses.

there was no mention of how much fluid is going into the overflow or how quickly. small amounts? fine maybe a pinhole in the reservoir tubing. large amounts? obviously something is overpressurizing the system forcing coolant out and replacing the coolant with air(sometimes an engine can pass the bubble test but that doesn't mean it doesn't have a popped seal/cracked iron). other possibility is simply a faulty cap, yes you can have more than one faulty used cap.

my bet is likely on a intermittent coolant seal leak but i didn't want to kill his hopes. the crack in the reservoir cap or pinhole is a good quick place to start though.

come on guys, i think you can do better.

 

Hi you might want to check the overflow hose itself. The hose is very long and it gets plugged up.
Just disconnect at bothends and blow thru. I had some dirt that had gotten trapped over the years and didn't allow the coolant to go back fromthe tank to the radiator.
Worth a try.
Paul

 

i had that same problem on my first (original) motor, and it slowly ran worse and worse till i had to rebuild it. although i'm sure mine was the coolant seal..

 

The two of you who were arguing about the thermostat/small seepage being the root cuase... were probably both right!

I pulled appart the upper goose neck from the water pump, and found that the thermostat gasket was beyond recognition. The remainder of it just about crumbled up in my hands when I removed it. When I inspected the thermostat, the rubber seal in it was damn well disintegrated as well, and did not make a complete seal when it was closed, hence allowing seepage through it AND around the gasket.

Well, I'm heading off now to pick up the new thermostat and gasket kit that I ordered yesterday and will post the results later.

Thanks again for the help everyone.

Cheers,
- TT

 

Unfortunatly the coolant saga continues...

After replacing the thermostat and gasket, I put everything back together and found that there was still a leak coming from the thermostat flange! Turns out that the goose neck had a small crack in it. (I felt stupid for not noticing it the first time and I think I might have made it worse when pulling the flange and thermostat apart).

At that point in time it was Thursday night and I decided to run with the small leak at the track day. Apart from having to move the fluid into the radiator between sessions, it didn't give me any other troubles, while having my eyes fixed on the temp gauge. The car ran great and I had an awesome time. The fact that it was COLD and very wet probably masked up any glitches in the cooling system that time.

Yesterday I bought a new gooseneck from Mazda and installed it... and it made no difference whatsoever! The fluid still flows into the overflow tank and doesn't come back. I've tried numerous times 'burping' the system etc, but no change.

A couple of things I did notice though was after I stop the car, I can hear a light hissing around the radiator cap (speaking of which, I've got a Mazda cap) and when the fluid overflows, there's a lot of foam that comes out...

Any ideas?

Thanks for reading, I'm actually looking forward to the day I can stop FIXING and start TUNING!
- TT

 

Foam is air, right? So, since you burped the cooling system and presumably got all the air out, it sure sounds like a blown coolant seal. This is a closed system, so I'm not sure how else air would get into the cooling system after you bled it. Take the cap off, rev the engine and look for air bubbles in the coolant.

 

Failed the bubble test??? I read in the archives that a jar of bars leak or block weld can seal the problem temporarily postponing a rebuild. Has anyone had experience with this?

Plz let me know

 

Damn you guys are just waisting money buying what's essencially a generalized auto part from Mazda. The Fd & Fd radiator caps are .9bar or 13psi. I just went to Advance Auto and bought mine for my Fd for 8 bucks and it was in stock. Just tell them you want a 13psi radiator cap for a Toyota Previa or any late model vehicle. LOL!

 

i just redid my cooling system for my s4tii since i overheated a few weeks back. Ordered a new koyo radiator and hoses, thermo and a new coolant o-ring (which is where i believe was the culpret). when i took off the coolant refill engineside, i saw a hairline crack on that part... so i replaced it with the coolant refill radiatorside and capped off the valve going to the resevoir... working fine and its actually cooling much much better... but of course due to the new rad. also, OEM mazda caps i think are almost fail safe i'm believing... had some autozone caps on before... was crap compared to IMHO.

 

I had the same problem before. Turned out I had too much coolant in the system! If you top off the cooling system it will always put some of the coolant into the overflow, without taking it back. It's not all supposed to come back. Unless you're getting the coolant buzzer, don't worry. But see #1 below. Or more likely you have the #2 problem below.

Other causes:
1. (from experience) Is your car running hot? That'll put more coolant into the overflow tank, and your aging cooling system might not be able to take it all back. With me the coolant came back after a few light drives in cool weather. Until then coolant buzzer went off until the car warmed up. I didn't worry because coolant doesn't flow through the radiator until the car warms up anyway. That was an old beat up '7, though.

2. (from Mazdatrix) The slightest leak in the cooling system will prevent a vacuum from pulling coolant back into the cooling system.

 

Thing is, I'm not sure how to burp the system properly any more. I read in the archives that you top up the level to the filler neck, leave the lid off and start the engine. Problem is, the moment that I do that, the fluid overflows from the filler neck within like 5 seconds!

So I devised my own makeshift way of burping the air out; by squeezing the upper radiator hose to get bubbles to come out of the filler neck, topping up the level and repeating until no more bubbles come out. I figure that being the highest point in the cooling system, that's where the majority of the air would accumulate.

Is this a good enough way of burping the system?

Even if I do that and leave the overflow bottle empty (after burping it out), it will still eventually overflow. Once the overflow bottle becomes full, and I jump into the car after it's cooled down a little, the 'radiator level' light will come on for a while, but after driving around for a few minutes will disappear. No sign of overheating. It's also looking like it's not drawing ANY fluid back in during cooling...

Hmm, will have to do a bit more looking into it this weekend. At this stage, I've stopped driving it all together (pools of green fluid don't look too appealing!). I'm pretty certain that the thermostat/flange leak was the only external one.

... how hard can it be to replace the coolant seal after all?

 

you just failed the coolant seal test, find a reputable rebuilder or buy a mazda reman.

this is not a joke btw.

and don't take offense to this but not noticing the crack in the thermostat neck leads me to believe you shouldn't attempt a rebuild on your own.