when i start my car COLD with the coolant fill cap off, there are no bubbles...

but when i start the car HOT with the fill cap off and let it run, there are bubbles all over the place. when i put the fill cap back on, pressure will build up in the AST, and when i release it, all the coolant rushes into and overflows the coolant reservoir. also, the car seems to be losing coolant into nowhere, but the exhaust doesnt smoke at all... i am seriously confused.

but the one thing i do know is i am somehow getting air pressure in my coolant system, and the coolant gauge is staying in the middle, not overheating at all... and i have never overheated the engine, so i'm curious as to how a coolant seal could randomly go out, if that is really the problem.

 

UPDATE:

i just started the car cold after it sat for about 4 hours. no smoke, and no bubbles when started with the coolant fill cap off... it seems that the air is getting into the system only when the engine is hot. anyone have any input?

 

Your system should build pressure to (what ever your pressure cap is) generally you won't see the bubbles in the system till the thermostat opens and you see the coolant flow through the system. You may beable to see the little bubbles before the termostat opens if you have a bad coolant seal on the motor but can't say for sure as I only saw them when the t-stat opened in my case.

 

i believe the problem is the thermostat being stuck shut, and the bubbles were because of the coolant boiling.

i just drove it to the gas station and the temp gauge started going up quick, and made it to about 3/4. so i coasted to the gas station, popped the hood to check stuff out... in FRONT of the thermostat was cold, and behind (engine side) was hot.

FWIW this is a crappy autozone thermostat, not a mazda one. i'll never do that again!

 

dud you have 5,677 posts, you should of know better, shame on you , specially fro doin it on a FD.



gil