I just bought a 1993 rx7, and the engine has been rebuilt, it runs very well and it doesn't over heat.

But every time i shut it off and get out i can hear the coolant boiling under the hood.

I'm going to flush the radiator as soon as i can, but do you think it would be ok to drive until then?


the water temp gauge stays just barely under halfway when its running.

 

Sounds like there's not enough coolant in your system or that you may have to bleed the air out of it.

Regardless of whether you fix the above you will still get that coolant bubbling sound from around the air pump area after you shut off the car but it won't be as noticeable. Obviously after you shut off the car the temperature rises hence why you get the sound but this is normal.

 

Yup. Just burp the air out and take a close look at your AST for leaks, especially if it's stock.

 

is it a boiling or a gurgling sound. a gurgle a couple minutes after shutting off is normal.

 

You should get a aftermarket water temp gauge. Just for your own safety.

 

the stock FD temp gauge has three settings, Cold, Ok, and Your Fucked.

By the time the temp gauge starts to register an overheat situation, you've already toasted your engine. Go aftermarket.

 

I had the samething occur with my car when I first purchased it and it was stock.
Once I replaced the Pre-Cat with a downpipe and put in a fluidyne radiator it stopped. My engine bay is much cooler with those mods completed. If you have a stock pre-cat, that thing is like a nuclear reactor under the hood!

 

alright, I bought some water wetter from auto zone, and i'm gonna flush the radiator today to make sure that there isnt to much water in the mixture.

I also got a new radiator cap.

I hope that will fix the problem, but if it doesn't i guess i'll work from there.

Thanks for all of your input

 

Did that work out for you? I noticed that sound too after driving my 7 gently (careful enough to not engage the broken 2nd turbo) for about half an hour. It was realllly boiling under there, and it worried me since I just replaced the AST with a stock original one (the labor was done by my dad, and trust me he knows what hes doing). There was also a little leakage around the top hose of the AST or possibly the cap itself (its the updated cap, 0.9 bar). My dad says it could be balancing itself out from some slight overfilling.

 

There's air in your system... take the cap off... and let the idle until all the air is out...

 

Here's an old post of mine. This stuff's all in the archive.

To burp the system, just start the car up when it's COLD and take the radiator cap off (the one that's NOT circled in the pic). Fill it with some distilled water (better yet, with winter coming, a 70/30 mix of distilled water and coolant) until it begins to overflow, and put the cap back on. Take 'er for a spin to let the car warm up, then cool it back off and repeat as many times as it takes. It took me about 5 or 6 times until it stopped sounding like there was a babbling brook behind my dash. You probably already know this, but our RX-7's run hotter than hell, so make sure it's nice and cooled off before you unscrew that radiator cap.


Here's a pic of a stock engine with the stock plastic AST (Air Separator Tank) circled. It's not my car or pic, so thanks to the owner..nice FD.



..and here's a link to a reputable vendor that sells an aluminum one.
http://www.rx7store.net/product_p/pettitast.htm

Also, a lot of people get rid of the thing altogether. If you search this club for "AST Bypass" I'm sure you'll find some informative ****.

 

mine is doing the same thing, its coming from my ast, and my add coolant light keeps buzzing, but the coolant is fine along with the temp. i'll try burping it as well.

 

I had the same problem. I replaced the stock radiator with a Koyo, installed a 185degree fan switch, 180 degree thermostat and replaced the water pump since I was already in there. I took the cap off the radiator (not the AST), filled up the system and started the car with the cap off. I then let the car come up to full temp. When the thermostat opened, I added more coolant. Then I made sure that there was plenty of coolant in the overflow reservoir. I eliminated the boiling sounds eminating from within the AST and the overflow reservoir.

 

i did exactly what the guy a few post up said just burped the system and its been fine all day

 

well, everyone explained EXACTLY the problem ive been having, i knew it wasnt boiling but the coolant light and temp rising had me worried, but ill go burp the system now and hopefully eliminate it.

 

alright... It's been a while since i started this thread, and im still having problems.

Two days ago I flushed the radiator (first time i just changed the coolant) so i'm assuming that there is just air in the system and im not burping it out properly.

I just start the car up cold with the filler neck cap off and heat on and continually pour coolant in there until it stays within 1-2 inches from the top correct?
I have done this a couple of times and I can still hear the coolant boiling from the overflow resivoir nearly every time i shut the car off.

I will do that again today, however, there is something else i saw that I don't think is very good at all. When i checked the level in the overflow, it looked like there was a little bit of oil on the dip stick.... what does that mean? blown engine? bad coolant seals? is there anything that could cause that, that isn't horrible?

 

alright, i just topped off the coolant. I let it idle with the filler neck cap off and heat on and topped it off as necessary, after about 4 minutes of idling the coolant started to rise, very very very slowly. It didnt rise more than about an inch so im not worried about it.

Also, when you guys say get a new radiator cap, do you mean a new cap on the AST...?

I'm still worried about seeing that little bit of oil on the overflow resivoir dipstick aswell. Please help me someone.

 

definitely get a new AST cap and a rad cap, cheap cheap insurance
I replaced the old AST cap on my Pettit Racing AST and magically my FD stopped spewing coolant

 

I had the very some concerns, my 1st 8 posts all had to do with cooling concerns. The big cooling thread on the 3rd Gen FAQ is a great place to start. I would replace both caps, the one on the AST and the one on the filler neck. Now, correct me if I am wrong but coolant will surge into the overflow tank when the car is hot and then it will pick it back up when it cools off, this makes a bubbling gurgling sound which is normal. Chekc the coolant thread though, I found all the answers to all my questions there...