Boiling underhood! What's it mean?
 

I got home from work today and parked in the underground garage. It's pretty quiet down there and as I walk toward the elevator, I hear this slight gurgling sound coming from the car. When I lift the hood, everything appears as it should, except for the coolant overflow tank. I guess the hose (the one that goes in there through the cap) is flowing coolant in and the tank was pretty full. I lifted the cap and could plainly hear bubbling and see steam.

What's it all mean?

The rotary gods are anger

could mean you have a void in your water seals.

It means your coolant heats up after your car is turned off. Once pressure starts to disapear it happens. My car does a similar thing for a few minutes. According to the the haltech it get to about 200. Unless coolant is disappearing you'll be fine.

Other than that, I haven't figured it out. Maybe someone else knows a fix. In my case it's not the seals, cap, or thermostat. I think mine is related to my Turbo and Exhaust.

I forgot to mention that my car is a '91 Coupe with 130,000 miles. With the exception of a rebuild kit in the Clutch Slave Cylinder and the various consumable maintenance items like spark plugs, all of the engine components are original.

When I'm on the freeway at higher speeds or have the A/C on, the temp needle starts to rise past the halfway point. But when I slow down or even come to a stop, the needle goes back to just below half.

I'm going to flush the radiator and replace the thermostat this weekend as a first step to solving this.

Since Dallas is gonna be consistently in the high 90s soon, any other suggestions to get this fixed will be appreciated.

Good idea. Be sure to use a Mazda brand thermostat.

Get a cap also.

Yes, I got the Mazda thermostat. What about a cap? Should that be a special part or can I get one off the shelf at PepBoys?

No, seriously...

of the shelf- just make sure it's a 13lb cap.

i know my moms jetta boil's so i think it should be fine my moms car is a 2001 so i dont think there is anything wrong with it

The S5 temp guage has three positions: cold, normal and "new engine". If the guage has moved from the middle position, the car is already too hot.

I have a page on troubleshooting cooling problems: http://www.aaroncake.net/rx-7/cooling.htm

I've had this before. In my case it was air in the system from replacing some coolant lines. Getting the air out of the system is not as easy as it would seem. At least on the '86.

Check the coolant level (in the radiator not in the overflow) then drive, let it cool, check again, drive cool, check again etc until all the air is out.

I also found squishing the upper radiator hose (with the car off) I could hear sloshing if there was air in the radiator.

That's a great set of information. I printed it and I'll give it the good read-over before I do too much. Thanks very much.