Gearhead

iTrader: (1)

My friend has a FD, and his car always makes a percolating sound when it's shut off. When I say percolating I mean it sounds like it's making coffee, but it's not. I always thought the sound was odd, but since there weren't any coolant loss issures, never thought much about it. Well, now there are coolant issues. It was spitting coolant out of the reservoir. I thought it might be bad coolant seals, but decided to check the cap and stuff first. Tonight I refilled it and cranked the car and let it warm up with a funnel (half full so I could watch for bubbles) on the AST. I refilled the car and watched for bubbles in the funnel, and there were a few as it bled itself. The stopped after a few minutes;I assume because all the air was out of the system. After the car warmed up it let a few more bubbles out... then it started foaming and percolating in the funnel. It sounded more like boiling than water jacket problems, though. I shut the car off, and the boiling/percolating continued for 5 minutes or so. The coolant temp remained normal through the process, and the fan cycled normally.


So... have any of you ever heard of this? It does it so hard the AST feels like someone is tapping it or something. I'm thinking localized boiling or something. Maybe the engine has a hot spot or something. Have any of you ever heard of anything like this?

Oh, the car has a Mazda reman with about 20k or so on it. It has made a percolating sound for as long as I can remember, and the engine had 9k on it when he got it. It's all stock.
Thanks for any info you may provide.
Don.

striker

its a fairly common thing with a precat. the precat is keeping the turbo's very hot, and the coolant boils in the turbo's after shutdown. get a downpipe, that fixes the problem.

Gearhead

iTrader: (1)

Funny you said that. I revved the engine a few times trying to make it do it, and after one time it did all of a sudden.
If anyone else has any ideas... let me know.
Thanks.

Trexthe3rd

Been there, done that.

What you are seeing is exhaust being passed to the coolant through a bad seal. Sorry bud, the cars days are numbered. Do a search under block weld, it's a temp bandaid but it seems to work for most people.

As for the pre-cat non-sense. If the car already has a reman and your friend is still using a pre-cat, then he deserves every bit of it, sorry. I didn't know anyone still kept their pre-cat. That's the number 1 engine killer, and everyone knows it. It's also the number 1 reliability/performance mod recommended by EVERYONE.

Gearhead

iTrader: (1)

That's pretty sweet of you to say someone deserves a blown engine. The car wasn't his when the engine was replaced, so he couldn't have made the decision of what dp to put on, and he just bought a full exhaust system. It was about to be put on. Next time a little tact would be nice.
So if what you're saying is true, the engine has had a bad seal since it had 10k mi on it, and it has had an additional 10k or so put on it without any problems. I'm not deaf to the possibility that the engine is bad, but in all my years working on these cars, I've never heard one make this sound. I guess I'll pass a gas analyzer over the neck to check for hydrocarbons.

Ward

just the percolating sound when it is shut off means the cooling system needs to be burped. the new coolant issues i dont know.

Gearhead

iTrader: (1)

Burped? Explain please. The car has done this for a few months now. I would think all the air would've made its way up by now.
Oh, and as far as blown water jacket seals go... It doesn't bubble in the coolant all the time, just after it gets warm. Every one with bad coolant seals I've ever dealt with (lots, I used to work in an RX7 shop) would bubble out of the neck constantly. I specialized in FC's though. We had another guy that specialized in FD's. I've built FD motors, but I've only put a few in. The whole cooling system is a bit foggy in my mind now.

cewrx7r1

iTrader: (2)

Run only 25% antifreeze, 75% distilled water, a bottle of REDLINE WATERWETTER, and a original pressure caps; and it will not happen anymore. Plus the engine will cool better.

tfhuth

I agree. Please post what you find out with the exhaust gas analyzer. I'm not convinced of a blown seal.

Tom

GoRacer

iTrader: (2)

I thought it was air when I went through that and (burped) bled the air from the system but that was not a fix. I did the 25% coolant, 70% water & 5% Purple Ice and it minized the boiling. When also using synthetic oil, the temperature lowers even more.

ZeroBanger

This is bull-****. Sorry, this is EXACTLY why people are scared to death that they are going to pop the engine.

When I bought my RX7 it had about 20K on the new engine and when I shut the car off it perculated just like you describe. It was very loud and obvious. I replaced the AST Cap and the Filler neck cap and the perculation stopped.

My engine compression tests are perfect, btw. That was 28K miles ago and my car has perfect compression , perfect seals and NO Problems.

Maybe you had the perculation noise and a bad seal, but they were not necessarily related.

es

Any time you have air in the system you lower the boiling point of the coolant. That means a leaky coolant hose would easily introduce air & cause boiling. 2 of these hoses are pretty small, go to the turbos (hottest part of the engine bay & very close to the pre-cat) and are completely hidden by the turbos, airpump, airbox, & IC pipes.

Yes the dealer would typically say "it needs a new motor & turbos" because that is the only way it's worth the time for them to fix it.

Now, one way to check to see if exhaust is getting into the system is to purchase a coolant system pressure tester & run the car. If the pressure is steady you probably just have air or a coolant leak. If the needle fluctuates the system is being pressurized by exhaust.

Do the tests first & make sure you have a healthy coolant system before you blame the motor!

tfhuth

Yep!

GoRacer

iTrader: (2)

Zerobanger and ES most excellent answers dudes!

Everyone allways assumes an engine rebuild (especially dealers) and people are taken advantage of. This forum was intended to share the knowledge and prevent that.

es

Thanks Goracer.

I would like to add a few details that I left out of my post. If you are using a coolant system pressure tester while the motor is running be sure to watch the pressure very carfully. The tester has no pressure relief so once the pressure gets up to about 9-12PSI you need to shut the car off & slowly open the valve to bleed off the pressure. If you just let it go you could cause some serious damage.

One commonly overlooked thing that can overpressurize the cooling system is a clogged coolant reservoir tank hose. Ants can crawl into the reservoir & die then get sucked into the low pressure hose clogging it. Then when the AST cap opens at it's designsated pressure the air & coolant can't burp to the reservoir because the hose is blocked...

Trexthe3rd

You guys are so funny sometimes. Not to be an a$$ or anything. But here is my personal experience:

1. Coolant comming out of the overflow.
2. FOAMING seen at the filler neck (Note. he said foaming, not a couple of air bubbles)
3. Constant tiny air bubbles seen at the neck
4. Coolant loss after fully warmed up.
5. Changed 6 new pressure caps of different pressure settings.
6. Eliminated ast, added ast back
7. Car ran for 14000 miles after the symptoms first appeared
8. Pressurized the coolant system for 24 hours, no aparant pressure drop
9. Nothing on the plugs
10. Checked coolant hoses for leaks, no leaks, replaced most of the coolant hoses anyway.
11. No stumbling at startup, no cloud of white smoke until the very last day before engine replacement.
12. The car ran excellent, I did 12.8 passes at the track

Does any of this sound familiar? You are right about doing the sniffer test. Because I have been searching and reading everything on this subject for a year and listening to all the "No, it's not a blown engine" from everyone on here, I was in denial for all that time. Thats where the bitterness comes from. It did however gave me the chance to have a thourough understanding of the cooling system in this car. I tore apart my old engine and rebuild it from scratch as a spare.
In the final analysis, the coolant seals can fail in a variaty of ways, and will produce different symptoms, some are very minor and will not show up using your typical test methods.
As for the "it wasn't his car, he had no choice" comment. The first thing I checked before I bought the car was the list of reliability mods done on it. What ever wasn't done was, within a month of the purchase.
It's funny how people are such hypocrites, what ever happened to "do the research before you buy the car"?
Anyhow I hope for your friend's sake it's not the seal.

Trexthe3rd

Under a pressureized cooling system, if there is a leak in any of the hoses, fluid would exit the leaking area and do one of two things. One, hit a hot surface and evaporate, causing a strong coolant smell under the hood. Two, create a puddle under the leak after shutdown (the system is still pressurized), and can be seen. The only time air will enter into the system is during the cool down process when the fluid contracts.
In either case, it would be easily detectable if you know what to look for.

Trexthe3rd

LOL, read the whole post, and not just the title. Especially the part about the FOAMING COOLANT!
When my seals had leaks, the car dynoed at 322 RWHP. perfect compression on both rotors, so? We are not talking about an apex seal.

Gearhead

iTrader: (1)

Well, do your research comes into play somewhat, but he bought the car from a rotary shop. The engine was new, and it was in good shape for $9k. The DP and the rest of the exhaust are in my kitchen. Awaiting me to have time to put it on my rack and put the parts on... but anyway, why should that matter since you seem to think the DP is a non-issue anyway.
Since I have quite a bit of experience with these engines, and I've never seen one act like this, and some of you have, I'm not jumping onto the bad motor bandwagon just yet. Not that it matters to me, my friend will pay me to rebuild it, but I want to do a through investigation. I'm sorry Trex, that you had a bad motor, but every ailment might not be that. Thanks for your critisizing input anyway.
Thanks everyone else too, I'll put your suggestions to good use. Fortunately for me I'm an automotive equipment dealer, and I have a 5 gas, it's just out on a demo right now. All I have to do is drive to the shop where they are demo-ing it, and tell them that I need to borrow it for a few minutes. Looks like tomorrow's project.
Don.

spurvo

I had MAD gurgling. Right at the top of the engine. Had coolant coming out the overflow AFTER shutoff too. Replaced all coolant hoses and the AST. The overflow was from leaking AST to Overflow line coupled with bad filler cap AND filler body pipe plug leaking. After all of that was solved, no more overflow, and NO coolant consumption.

But still gurgling.

Did the complicated version of the fan mod. I notice my turbos glowing lightly before shut off, so I cycle the temps using the fan switch to keep the temps below 200F. So three cycles, from 177F to 200F and back again, and the turbo glow is gone. If I don't do this, gurgling sound. If I cool the turbo, NO GURGLING. And I mean it. None.

You are seeing the turbo heating up the coolant. Note that the turbo housing is subject to exhaust temps, which run 650F at the COOLEST, and up to 1800F during part throttle cruising. So even with DP reducing the temp held by the turbo housing, it still reaches 1000F or more. The coolant moving through here will reduce this somewhat, but we still have flash temps at the coolant of WAY over the boiling point of even an Evans 0psi coolant system (like 325F or so?). So I'm gonna vote that the gurgling and foaming boil over (especially AFTER shutoff, when leaking coolant seals CANNOT be the problem!) is from hot exhaust. DP helps, but fan mod REALLY helps.

My $0.02.

ZeroBanger

My point is perculating coolant is not related to o-ring failure or any seal problem. Your seals were going bad, thats too bad but it had nothing to do with the perculating sound.


david

Kento

Siding with Spurvo on this one. I had the exact same symptoms (except the coolant coming out of the overflow). Gurgling noises after shutoff. Noticed in a dark garage that the turbos were glowing a dull red. Ran rad fans at idle for a while to drop coolant temps (even had a fan blowing on the oil cooler), until the turbos were no longer glowing. Shut down again-- no gurgling or boiling noises, or if there were, they were very small and random, far less than when I had first shut down. Haven't experienced any coolant loss either.

Doesn't take much to get the turbo housing glowing red. Even a short run through the gears will get it glowing, and despite cruising off the boost for several miles to cool things down, the housing will still be glowing a dull red if you check it out in the dark.