I had the coolant flushed and replaced by a well known rotary shop here in the northeast when they were doing some other work. Ever since - I cannot get the system to stop bubbling and gurgling when the engine shuts off. I added some more coolant as the days went by - following all of the posted instructions here on the forum and all of the help sites. It still makes a ton of noise (like boiling)
I followed all of the standard advice - remove the fill cap, burp/pulse the large radiator hose on the bottom left. I even removed the throttle body hose and burped it that way. The overflow tank is at the full line (in fact there's a little extra) and the fill reservoir won't fill anymore. This thing is full! (BTW- I have never experienced any overheating issues and I have the stock radiator). Anyone have a suggestion?

Thanks a lot.

 

Maybe still some air in the heater core though I've never had this problem burping at the TB. Find someone with a vacuum pump maybe to suck out the rest.

 

put a higher psi cap on both the neck and ast if it is too low, this has been known to cure the gurgling problem.

 

do you have your heater on high when trying to burp the system? perhaps its like impactwrench said, you might have air still in the heater core.

if you do have an airbubble, perhpas you might wanna go back to the garage or some other radiator shop and have them vaccum the system so there is no air and then refill when still under vaccum to make sure there are no air bubbles (saw this on american hotrodder. I think they were building up the alumatub. it took them about 3-5 tires to get rid of all the air in the coolant system and during the entire time, it confused the crap out of them). you might also want to have your coolant system pressurized to test if there are any other leaks. the radiator shop/garage should beable to do this or you can go to sears and buy a kit to do it yourself.

as for increasing radiator cap pressure, i dont think you should need to do this at all, im totally against this idea even though it might possible be a quick bandaid fix. especially if before hand it was doing fine. you should have the 13lb cap or the .9bar (which is the same exact thing). you might wanna search to see why im against this (there are many threads about this topic, heck there is even a tsb about it).

 

I can think of two things that could be causing this:

1. Too little coolant in the mix. Ethylene glycol has a higher boiling point than water. You might want to ask them the ratio of water / coolant that they added.

2. Low cooling system pressure. Your radiator cap might be failing to hold pressure, or you might have a leak somewhere else. Adding pressure to the cooling system will raise the boiling point of the fluid, whatever the water/coolant ratio might be.


Just a side note: a highly pressurized cooling system is not always a bad thing. Water has the best heat transfer properties, and raising the pressure will allow you to use a higher percentage of water without boilover issues.

The bad thing about increased pressure is the additional stress it places on your hoses. The factory hoses will be more likely to split or come loose when you increase the pressure of the system. From my understanding, this was the main reason for the TSB that skunks mentions; the hose at the throttle body would pop off if the car was turned off while the engine was very hot. (racing w/o warming down).


Here are some FAQ links you might find helpful, especially the first one:

Coolant Burping Tool/ Radiator Cap Funnel
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/radiator-cap-funnel-eliminate-air-bubbles-342309/

Coolant hose part numbers: replace all the rubber coolant hoses in your system.
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/all-coolant-hose-part-numbers-331644/

Cooling / Radiator Fan Control information:
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/coolant-recall-fan-controller-schematic-location-385773/

Cooling fan modification. Lets you run your fans when you want to run them:
http://www.scuderiaciriani.com/rx7/fan_mod.html
http://rx7.voodoobox.net/howto/fanswitch/fanswitch.html

Cooling system diagram:
http://www.autosportracetech.com/RX-7/coolingsystem.htm

-s-

 

Skunks and impactwrench - I never thought about the heater core. I'll do the heater trick.
All great advice. Thanks for the links Scotty. I appreciate the help and I will try some of these new ideas.

Dave

 

somebarry with cooling system diagram for FC ?

 

Sorry for the bump but i didnt want to make a thread for such a vague question.

Basically im concerned with something.

Yesterday i took my car out. I dont drive the car often so i check basic fluids and do a look around to make sure everything is ok with the drive. I check my oil, its good, smells like gas a bit but i knew that, im going to change it next week. Checked my coolant and opened up the filler cap and coolant sorta "squirted" out. Like it was still under pressure. Not much came out but its like it was waiting there since my last drive. Which was 6 days ago!!

So im thinking whoa thats not normal however not the first time i saw this. Last time i saw this, a couple of months later my AST cracked on the top weld by the rim.

So now im nervous. But i go for the drive anyway cause im not going far, nothing can go wrong.

Stupid thing of me was trying to boost when the car was cold. My car is non seq and i was merging onto the highway and i tried to boost in 2nd, it bucked and missed and i knew that was going to happen. My gauge was reading like 120-125F. This happened before, not really part of my question but just adding it in to complete the story.

So anyway i drive it more to let it warm up, then it boosts properly. Yay im happy. I go home, back the car in my usual spot in my backyard and shut her down. Go out, close my gate and notice something dripping underneath my car. I go look and there it is again, coolant.

I pop the hood and coolant was oozing from the bottom hose of the AST. Almost like if the hose clamp wasnt tight enough. I was trying to fiddle with it but everytime i moved the AST, more coolant is coming out.

So im like wtf, is the AST cracked again?!?!?!?

Its too hot for me to touch it more so i go back inside while the engine bay cools down.

About 35 minutes later i go back out, engine bay is nice and cool to the touch. Took off the AST mounting bracket so i can inspect thoroughly. No signs of a rip on the bottom rubber hose. I pressed on it to see if coolant would come out. Nothing. I shaked the AST to see if coolant will come out. Nothing. So where was this coolant coming out of then?

I looked closer (a bit hard cause it was getting dark) and i noticed the green, wet mark just where you put the hose on the bottom nipple of the AST. Like there had to be a 2mm gap of nipple left where coolant can ooze on out there. I checked the hose clamp and it was tight though, but i turned the clamp 3/4's of a turn anyway to be safe for next time.

NOW, here is my question or series of questions.

Do you think me trying to boost while the car was cold contributed to an overpressure of coolant? Or is rpm's dependent on coolant pressure in some way? Stupid question i know.

And second. Why would my coolant squirt out of the filler cap like that when i havent driven the car in 6 days prior to that?

FYI, AST cap is 3 months old, 13lbs. I burped coolant system VIA pressing the rad hose to the filler neck as i added coolant also 3 months ago when i changed a coolant hose.

Another FYI, i think i lost about a little over a pint of fluid from the look of it HOWEVER when i opened up the filler cap. I could still see coolant in there. I may have lost about 2 inches worth. (if you look into the filler neck, the coolant is like 2 inches deep and just sitting there).

So i also think maybe i over filled on coolant and it had to shoot out of somewhere? Or maybe since the T-stat closed from the cooldown, im really empty but im not? I have no idea.

Please help and thanks for those who actually read this long story lol

 

Bump for anyone who knows whats up with coolant system pressure when car is cold.

Its been 6 days since i started the car. Today when i opened the filler cap to check for coolant, it coughed out some coolant like it was still under pressure (cap didnt have any pressure though).

What could be the problem?

 

"Do you think me trying to boost while the car was cold contributed to an overpressure of coolant? Or is rpm's dependent on coolant pressure in some way? Stupid question i know."

No, I don't think you trying to boost the car when cold would contribute to that.

 

Yeah, it happened today again btw.

This time i felt a slight pressure of the cap, almost like it burped but there was no coolant spill. This is because coolant was a bit low (i recently finished a coolant hose replacement so im still doing the adding thing etc).

Do you guys think its the thermostat?

AST cap is still new, about 5 months old, 13psi cap.

 

On the RX-7 (as well as the Miata), coolant continuously flows through the heater core no matter the position of the heater control. That only directs air either around the core (cold position) or through it. There is no coolant valve in the heater control system.