shred

Well, this is my first posting to this site, believe me when I say that I check all the threads for something similar to what is happening to my RX-7 pain in the @#$@% right now.

Some simple background, sweet car, bought it off a complete idiot, engine has been replaced, everthing is in top shape and everything works. Currently the car is stock except for a cat back exhaust (the original started to literally fall apart).

I was planning on getting into some after-market fun but this little &%$$F# stuff is driving me crazy. From vacume hoses to throttle body adjustments, this is the first time I have had to work on a car so much without a manual.

So what is the problem right now?? My car runs perfectly, but no matter how long you cool it off after running it, the radiator will pop in about 15 minutes from turning the motor off. When I say pop, it is just like a regular boil over.

I haven't tried to replace the cap yet but based on how the car is running (and I also need to change the plugs) I was wondering if the pre-cat can be causing this, super heating the turbos after shutdown with the crappy burn from the plugs I need to change??

So am I close or really far off?? I can't see any other leaks and the temp on the interior gauge never gets above the middle. The AST is new but I don't know about the cap on the pump.

skunks

are you cooling off the car properly by popping the hood and letting it cool off (and this means every time, not just when you come home)? This means having your radiator fans on high, parked into the wind, if no wind; mount fans on wall and point toward car, turbo time for 2-10 mins depending on how hard you just ran the car before you came home? if not, why not?

Also, what psi is your radiator cap? What is your water to radiator ratio? Usually when your coolant boils off, it goes in to the over flow tank... You might have a coolant seal which let go...

In anycase, I recommend you getting a dp and mp asap! (dont forget the boost controller)

maxcooper

Do you just get gurgling, or do you get a pool of coolant on the ground?

Are the AST and filler caps in the right place? The filler cap is plain and the AST is a normal radiator cap with a spring underneath it. If they are swapped (plain cap on AST), the car will boil over a lot.

-Max

13brv3

IMO, this is a little excessive. For goodness sake, the car was made to be driven daily, like any other car. You just don't NEED to do all this. In fact, you could probably make a case that rapidly cooling the engine is worse than letting it cool naturally.

Back to the original question-

- First, if you need a manual, you can buy one from a number of places, or you can download one here:
http://www.scuderiaciriani.com/rx7/shop_manual.html

- As for the boilover, what are you running for coolant? It's not just straight water is it? You did say you bought it from an idiot

Good luck,

shred

To clear up some of the confusion, and help to get some direction, the motor is brand new Mazda put in by a half-way decent dealership out here. Other then a disagreement with the throttle body and adjusting it, they did a rather good job.

Under the hood is stock, the two caps look pretty new but I can't tell if they replaced them when they changed the engine or the AST Tank.

As for the problem, no I don't open my hood to cool down, I assumed that the engine under normal conditions without mods dosen't require additional radical cooling steps unless I am racing it. I do drive pretty fast, lets face it, if I wanted to go the speed limit I would have purchased a Hyundai or a Yugo.

The problem is new and coincides with the first time running the heater in cold weather, and the engine warning light comming on at idle after the motor is warm. Tap the gas and the light goes out.

Checks, coolant is topped off and the boil over doesn't really loose too much coolant. Add about 2 cups and it is back to topped off. The drool is right under the over-flow tank. I run straight glycol (probably should move to wetter water) as far as I can tell from looking at what came out.

No leaks to speak of other then this. Did read a recall on these cars that does match this pattern. Boil Over after shut down due to improper cool-down can lead to under the engine fires sparked by pooled coolant on the engine that falls on the exhaust manifold. Pretty nasty results if you ask me. The expected problem was the turbo exhaust manifolds on the 93-94 TT RX-7 but the Mazda Company instead put a nifty little alarm and light on the neck of the pump fill point to alert you to a potential problem.

As for the Caps locations, they are the right caps on the right equipment - AST cap on AST, and radiator cap on pump neck.

rxrotary2_7

sounds like a water seal to me. the few things you can do with high hopes (but most likly are not the case) replace the cap and thermostat. only use the OEM thermo from dealer. other than that, there is no reason why the overflow should, well, overflow...there is some presure being put into the coolant system from the combustion chamber.
next time car is cold, open the cap and start the car. do you see little bubbles? if so you have a bad water seal my friend. you cna also use a collant system presure tester. does it hold thre pressure or slowly fall off?

13brv3

A few other comments-

You said you run straight glycol. I have to assume that you mean without any other additives. If you're running 100% glycol, with no water, that would be bad since glycol doesn't cool as well as water.

Pardon me if this is a dumb question, but I have to ask... is the level correct in your overflow tank? If it's too high, you might just be pushing out some water during heat soak. If it's empty, you might have a crack in the tank.

As for the engine light, I'd look for a code on that to see if you can find out what it means. When you tap the gas to get the light to go off, does it come back on when you let it return to idle? That would make me want to look again at the throttle position sensor.

Good luck,

shred

Normally with regular motors, if you have an internal sealing issue, you will see it at running, boiling over as it adds gasses to the pressure of the existing cooling system. That is not my problem. My problem is when the engine is not running.

The engine never gets over mid-temp. I am not running 100% glycol, it is mixed with water at the ratio required for the car by the manual.

The overflow is not leaking, both caps are seated correctly and are on the right equipment. Everything seems to be working correctly (less the boil over at shutdown).

The Engine Light is most likely A/F at idle. You tap the gas and it goes out and doesn't come back on. It doesn't always come on when the car comes to idle, about one of every 10 times, only lately. Plugs have about 3k miles on them, not too bad but I had some other issues that would have accelerated the fouling.

So I am looking for heat soaking issues after shutdown. Where is it comming from?? I don't know. Pressure is introduced to the coolant system after the car stops running that is exceeding the caps pressure capacity, it pops and runs out the overflow.

Since the car is at mid-temp when running, it must be something that doesn't have a cooling jacket on it or the water temp would be much higher. This has lead me to the pre-cat. Does anyone still have the pre-cat and had this problem? My car has about 97,000 miles on the pre-cat, more then enough to plug the hell out of it.

13brv3

The overflow line for the AST cap goes to the overflow jug. The only way you should have water on the ground is if the overflow jug is filling completely, and the coolant is coming out of the hole in the top of the jug. Is that what's happening?

When you add water, where do you add it? If everything is hooked up properly, you should NOT have to add to the AST or Fill cap unless the overflow jug has been sucked dry. If you keep finding air in the AST or fill cap, and the overflow is not empty, there's really only one other place it could be coming from...

I have to agree with Mr Moderator (rxrotary2_7). You may well have a bad seal. Do a search for bad cooling seals, and you'll find plenty of folks that describe your problem as a bad seal. Strange but true, it's not a regular motor.

Overheating is the major killer of these seals of course. Was the new engine put in while the previous idiot owned the car? Any chance he overheated it?

Also, do you know about the non-linear water gauge? Mazda made this sit at one spot for almost the whole heat range of the engine. In other words, it quickly rises to a certain spot (a third of the way on mine), then sits there for the next 40 degrees or more. When it starts moving again, your virtually screwed already. I've heard it referred to as a 3 stage indicator. Cold-Normal-Rebuild.

I sure hope you don't have a bad seal, and if you do, I hope Mazda replaces the motor under warranty.

Good luck,

Flyrx7

iTrader: (1)

I would be more inclined to agree with 13brv3 above when he says you may have too much coolant in the system. Depending on the coolant you use (I have Evans coolant) it will/may expand a little with heat. I had mine overfilled (new engine) and it puked a couple times too. Check the level in the filler neck at the thermostat housing next time it pukes, if it is reasonably full and the coolant buzzer doesn't go off I'd leave it as is. That, and do the fan mod and get a downpipe. The fan mod is a no brainer and the DP also nets pretty good HP, but more importantly it won't cook your turbos and anything else in the near vicinity. Good luck.

Regards,
Frank

shred

Trying to pull some information here that makes sense. I thank everyone who has posted but I don't think that anyone has hit the problem yet.

Boilover, pressure exceeds caps limitation, cap diverts pressure to AST, AST spits to overflow, overflow - overflows to ground.

Since the pressure is gone and boiling has occured, gas has come out of the coolant and takes up the space that the liquid would normally occupy, hence there is now a vacume of coolant in the motor after a boilover.

So long as you keep the coolant at constant pressure, the gasses in the coolant stay in solution, expansion is taken up through pressurization.

So is there a leak on a valve? If you don't get any problems when the engine is running why would there be a problem when the engine is stopped?? There is less gassious pressure in the combustion portions of the engine after stopping then before when the chambers are igniting gasses. I should see boiling when the engine is running if I have a bad seal, not when it is stopped.

The engine was installed after I purchased the car from the dealership. It is still under warranty but I don't trust nor do I want to afford their BS fixes that got me here in the first place.

Now the weird thing that I don't understand is why after 15 minutes from stopping the car does the car boil over?? I built and owned a 9 second Mustang that blew head gaskets like they were going out of style (21 lb Intercooled Supercharger), that boiled the water while running, very easy to see and you get crap in the coolant. Here no crap in the coolant and no bubbles while running. Level on the overflow is right where it should be by the gauge. I filled at the pump neck and the overflow bottle. Still after a 10 minute cool down it boiled over, just takes a really long time.

So from that I am getting pressure in the system after I shut the engine down. Now how can that be a bad sealing cooling system??

Someone help me to understand how this is all fitting together, nothing so far is making sense, especially the hozed engine.

This sucker uses almost no oil, doesn't blow smoke or anything else through the turbos, what gives? Perfect vacume and pressure, turbos cross over just right, very tight operation.

Flyrx7

iTrader: (1)

I still say you have too much coolant in the system, see my post above yours, above this one...
It doesn't sound like a bad coolant seal to me, that would pose a problem while you're running, not with the engine stopped. If it's not a mis-placed coolant cap or a malfunctioning cap then it almost has to be this.

Frank

alwan16

check your overflow tank for tiny cracks that only open up when the coolant and tank are super hot. i had a leak from there and it only spilled out coolant after shutdown. don't just to conclusions too quickly especially since you have a new engine. i would also replace the caps, hoses, and thermostat and do a pressure check. good luck.

shred

Based on the general consensus of everyone here, think that the pressure test is the best bang for the buck.

I really appreciate the help here, the information out there is too confusing about these cars with nothing to go on.

There is a pretty good place that will do the work for me at a decent price. Wish me the best, will post the results so hopefully nobody else will have to go through this confusing hell. Maby give a few veterens a chance to do the old 'I told you so'.

Will replace the cap and let her gugle once before going over to pressure test, just in case may save me quite a fair bit of cash - which I need to get closer to getting rid of this nasty Earl Shibe paint job on this poor car.

dclin

iTrader: (4)

It sounds like you have a pretty good grasp of what direction to look in, but if you would like local help - or, at the very least, some connections to the Houston 7 scene - there are a few resources:

http://groups.yahoo.com/group/htxrx7/ (http://www.houston-rx7.net/)

Maz-Max (W Little York, just east of 290) 713-896-8005 if I remember correctly. Ask for Bryan Smith - service manager, 2nd and 3rd gen owner and long time HTRX7 member.

www.turbostreetfighter.com ,Marcus Williams. Out in the Copperfield area. He really only likes to do performance stuff (specializes only in 3rd gens), but may have some ideas on your coolant problem.

We've got some very knowledgable 7 guys here, like Chuck Westbrook and the other usual suspects, so you live in the right place.

Welcome to the club.

spurvo

Want to interject one thing here...

I had the EXACT same problem as you describe. Engine runs fine, temp not too high (though stock gauge total waste of dashboard space... until you linearize it. Then less so), topped off the coolant, everything is fine. I drove it, parked it, even popped the hood to cool it off. Inevitably, ten to fifteen minutes, and... peeeee, right from under the pass headlight (overflow tank, duh!)

Problem? ENTIRE coolant system not sealing properly. First, I found the pipe plug on the filler neck was leaking. Next, I found the filler neck cap was sooooo ooold that the rubber CRUMBLED in my hands. After I fixed these two, I figured I had it made. Uh uh. The last place was the overflow tube itself was not properly sealing to the AST. I zip tied that and that bullshit stopped. Then it was just the bullshit with constantly dropping coolant levels. 14 coolant lines later, all is well.

The deal here is that the overflow has to make a vacuum tight connection, just like the rest of the sytem, such as the caps and the pipe plugs. First you fill the system and the overflow, then you drive. As the coolant heats up, it flows out the pressure cap on the AST (NOT the cap on the filler neck. This is a "one way" cap that just holds pressure. They put the filler there 'cause it's the highest point in the system, other than the block to TB hose in the back) to the overflow tank. After you shut off the engine, the temp and therefore pressure in the system stays high for about ten to fifteen minutes. Then in finally starts to cool. As it does so, the mass of the water/coolant shrinks, reducing volume in the sytem. This creates a vacuum in the system, which pulls coolant back from the overflow into the AST (which is why the AST has the "two way" cap). IFF the coolant system is not vacuum tight, the system just sucks air, and all that extra coolant ends up getting peed all over the ground. The extra volume is coming from repeated fillings of the filler neck.

OK, that LONG post ultimately boils down to making sure your hoses are not leaking (except for pinhole leaks that only leak when the system is hot and pressurized, and seal up on cool down. These SUCK!!!), including the line from the AST to the overflow. Don't forget that there are TWO plastic inter-connectors on this line, one under the intercooler, the other under the air box. Tie wrap these as well. This should take care of it. Your instinct and experience are correct, overflow while running, blown seal (or head gasket in cylinder engines, MOPARS do it too!). Overflow AFTER car off, leak in system reducing or eliminating the ability for coolant to be drawn back in.

Hope this helps in any way. It was fun to write...

shred

Those make tons of sense.

As for the hints on the people to talk to, thanks. I have been emailing Marcus, actually picking up some plugs from him tomorrow.

Maz-Max is also on my favorite places to visit list. They will probably do the pressure check if it gets to that.

Thanks, I think that I have a good direction to head in now, I have seen a few small leaks on the line from the filler neck to the AST but I didn't think anything of it.

Anyhow, sure that Marcus will be able to take some of this great advice and come up with something. He is trying to get me to take off the AST with the filler neck bypass. Know that it fixes tons of problems, just not sure if it is the best idea. Such a pain in the *** little canister must be there for some reason?? I read all the threads here on it, totally strange that the company that made it didn't really comment on why thay put such an achillies heal on an expensive engine like this.

I saw a few others out there that have an upgraded fan that live in Houston. Got any tips on that?? Car gets pretty hot in the summer time, even with the AC on. And whats this linear upgrade for the temp sensor?? If it makes it more accurate, am all about it, not like there are any numbers on the original one anyhow.

Get me goen, want to drive this thing for at least one week without it breaking!!

spurvo

check out this thread

https://www.rx7club.com/forum/showth...ght=temp+gauge

or go directly to

http://www.iluvmyrx7.com/3rdgen/how-...auge%20mod.pdf

link is slow, but will come up..

Basically, the gauge now has the needle at the cold normal position (second mark from the bottom) during freeway driving, when the thermostat is controlling the temp (180 F or so). The needle points to just above the middle when the fans come on with the lights also on (210 F). I haven't waited to see where the needle is for lights off fan turn on (220 F, I think). Some folks love to see numbers. I just want to know it the temp is "normal", or if I should pull the hell over NOW!!! I like the mod personally. Digi-Key has all the parts in stock, didn't cost much, easy to put together if you can solder a little.

spurvo

Also, if you need some of those harder to find hoses, try mazdatrix.com. They have them ALL, ready to ship. Happy hunting

maxcooper

You made two comments that make me think the caps are in the wrong spots:

"AST cap on AST, and radiator cap on pump neck"

"Boilover, pressure exceeds caps limitation, cap diverts pressure to AST, AST spits to overflow, overflow - overflows to ground."

The correct placements:
- "radiator" cap on the AST (this is the more complicated cap)
- plain cap on the filler neck

When the pressure gets too high, the cap on the AST vents the coolant to the overflow tank. The filler neck cap never vents, and there is always pressure in the AST.

Your symptoms are exactly what you get if the caps are in the wrong spots, or I wouldn't mention the discrepancies.

-Max

skunks

i doubt it, but its your engine/car, do what you want to do.

13brv3

It sounds like you've got two good theories going here. One is boiling after shutdown, and the other is sucking air during cooling. If it's boiling, you'd have to imagine that it's happening at the turbo lines, but we can worry about "why" later.

How about this for a quick test- Have some fans standing by, and drive the car enough to get it hot. Bring it home, open the hood, and get the fans blowing to cool it off quickly (particularly in the turbo area). If you can assume you cooled it enough to stop any heat soak issues, this should point out the problem.

My money is on the boiling theory now, but then I've been wrong a couple times already

Good luck,

shred

As far as the location of the caps, I hope that they are not wrong. If they are it has been like that since the engine was replaced at the Dealership. Weird since this is the first time that there has been a problem. Guess that a better description is in order. The cap with the two ears is on the pump filler neck, this is the one like a radiator cap (well they both kinda are) and the AST cap is a completely round cap with no ears. Will get my digi camera out and charge it up, send you all a pic. Who knows, maby they are on backwards, after some of the problems that I had from the dealership, wouldn't be surprised. Really does take a sick company to make both caps fit on each others neck. Considering the consequences of a failure here, would believe that they would at least try to keep the things separate.

So will do that tonight when I get off work, settle this once and for all. Maby drive it so everyone can see the spittle of green juice from underneith.

adam c

iTrader: (2)

You may be able to check with Mazda to see where your caps go. Write down the part number from the caps and call them. They should be able to tell you what part number goes to what.

If you have the stock AST, get rid of it. Buy the Petit. It's not cheap, but it won't fail.

Do the fan mod. It won't solve your problem, but it may cool your engine enough to help.

spurvo

Cap differences: Pressure only cap, for the filler neck, will have only the rubber gasket under the top of the cap. Should be held on with a rivet that goes through the cap.

Pressure relief/backpressure flow: has the gasket mentioned above, but also a spring that extends down over a shaft to a round metal part with it's own rubber gasket. This second rubber gasket and spring assembly are what control the flow back into the system during cool down as explained above. This cap goes on the AST. The original cap had a pressure rating of 16 lbs, or 1.3 Kg. This was the pressure in the system that had to build before it would open and allow coolant to overflow. This gave a higher boiling point to the cooling system, as pressure is what prevents boilover. The pressure was too high, however, and so Mazda in its infinite wisdom changed the caps to a 13 lb system during a recall, or 0.9 Kg. From what I've read, go with the 13lb cap for the AST. Make sure it has the lower metal circle with the gasket and the spring.

Does this help?