My car is misbehaving. For the past few days after i drive i can hear coolant boiling or bubbling in the radiator but not into the overflow tank and the temp gauge stays at halfway. today, i drove it to my girlfriends house and when i was waiting for my turbo to spool down i noticed that the temp guage was at 3/4 and climbing so i immediately turned the car off. when i opened the hood it was steaming and the overflow tank was boiling. i let the car cool down for about 2 hours then put about 3 gallons of water into it. i then drove about 5 miles to a resturant and by the time i got there the temp guage was at 3/4 and i was steaming. after dinner, when I started the car it had only cooled down to halfway. then as i was driving back to my house it heated up to 3/4 and was rising, so i turned into a parking lot and when i was driving more slowely the needle started falling but when i stopped it quickly started rising. I turned the car of and let it cool for about a half hour, until the needle was at 1/4. i started driving home again and the needle quickly rose to the lower hot line by the time i stopped at a 7-11, maybe 3 miles away. i put into the radiator and after it cooled to 1/2 i drove 5 miles to home. the needle stayed at 1/2, even when i let idle for 10 mins. what is going on?

 

It could be a lot of things, such as air in the system, a leak or crack (usually at the cap) causing depressurization, a bad water pump, a restriction in the system, etc. In most cases it's a bad thermostat. Replace the thermostat with a Mazda brand thermostat, and see if that helps. See the Factory Service Manual for the thermostat installation so that you don't put the jiggle pin in the wrong place. The tightening torque on the thermostat cover bolts is 14-17 ft-lbs, and it will get ruined if you over-tighten them too much, so try to use a torque wrench. When you are done, refill the coolant per the factory service manual to bleed the air properly.

How-To's/Manuals
http://fc3s.org/

 

As far as boiling sounds go, I just recently had the same problem. The radiator cap next the overflow tank is designed to hold 13 psi of pressure (.9 bar). When the coolant pressure exceeds this level, it pushes the spring-backed plunger in the cap open and is collected in the overflow tank. If your cap is failing, the plunger is opening at a lower pressure (mine was opening at 5 psi). This means that the really hot coolant is now able to boil because the pressure isn't high enough to keep it in the liquid phase, and so it blows right past the radiator cap into the overflow tank and you hear odd boiling noises after you park your car and turn off the engine. I replaced my cap and the noise just stopped completely. Hope this helps, good luck.

 

Oh yeah, when you add coolant, if you're not in an emergency situation, use a 50/50 mixture by volume of antifreeze and DISTILLED water. The antifreeze lowers the freezeing point of the coolant and raises the boiling point. The reason for distilled water is that it has all contaminating ions removed, whereas tap water has calcium ions in it. In high temperature conditions, calcium ions can react with water to form insoluble calcium hydroxide (i.e. scale, which you don't want in your cooling system) and hydrogen ions (acidity). Acids are BAD for metal. If you have any familiarity with chemistry, this is what happens:

Ca (2+) + 2 H2O + heat --> Ca(OH)2 + 2 H(+)

This is why you need a coolant flush preiodically Hope this also helps, good luck

 

It's actually 35/65 above +3F, 45/55 above -15F, or 55/45 above -40F according to Mazda's recommendations. I used 50/50 when I was in North Carolina, but I went back to 35/65 for Florida.

Here's a US max/min temperature listing for the paranoid:
http://www.geobop.com/World/NA/Topics/Weather/Temp/