i was adding some water to my car while just after i had driven it (so it was still hot). of course a whole bunch spurted out when i first took the cap off, but after adding a bunch of water, every now and then it would all of a sudden boil over again. that happened a few times until it was full. what the hell? is it air bubbles in my cooling system? if it is how do i get rid of them?

 

You don't get 200+ HP from 1.3L without making serious heat. Also you gotta know that overheating will seriously shorten the life of your motor.
Here is a check list:
1) Replace the thermostat. Make sure it fits. The spring loaded disc on the stat must close the bypass port, or guess what?
2) Replace the radiator cap. Low pressure = steam bubbles = spit out coolant.
3) Look for leaks. (same symptoms as #2) Some can be very hard to find. You may have to pressure test it. A common failure spot is the 3/8” coolant line that runs from the top of the rear housing (under the intake runners) to the throttle body, to the BAC, to the water pump. Another one is the heater hose under the oil filter.
4) The fan clutch will slowly start slipping as it ages. The fan should pull really hard up to about 4k when the motor is hot. It should maintain about 4k as the motor revs higher. Sometimes you can get more life from it by bending outward the bi-metal strip on the front of the fan clutch. The cut-in for the series 4 fan clutch is gradual – it pulls some even when cold. The series 5 fan clutch is more on/off.
Good luck..
Bill

 

my thermostat is a brand new mazda one. my rad cap is crappy, but this is with the cap off. whats happening is after my engine is off, and after it initially releases pressure when i take off the rad cap, if i wait a minute or two with my cap off, it will all of a sudden boil over again.

 

Man, that is weird. I never got boil over, even after a hard drive. How full is the overflow tank getting?

 

If I understand correctly, water is more likely to boil when it has contact with air, so perhaps you shouldn't remove your cap while the engine is still warm (not to mention that's rather dangerous) Also, does your car run abnormaly hot? Have you checked for leaks?

 

Hey SureShot,

Thats a good point there. Actually all of them were good, this one just struck me curious.

Anyone know what the average life of these fan clutches are, or when they had to replace theirs?

Later,
Salguod

 

The good news - This could be normal - the shut down but still heat soaked engine transfering heat to the coolant that can now only handle ~220 with the pressure cap off.
The bad news - a possible internal leak allowing combustion gasses into the water jacket making a hot spot. The gases bubble out when you open the cap, then the coolant hits the hot spot and boils out.

 

My 87 fan clutch seemed go get tired after ~150000 miles.
I replaced it at 180000.

 

when i'm driving my car runs around 185f but if its hot outside and i let it sit idling in the sun, temps go up to 225, almost 230.

 

whats your antifreeze to water mixture %??

 

around 50/50