For some reason my car keeps losing coolant slowly, i gotta refill the reserve tank like every week. So I looked around the forums and decided to try and run the car with the radiator cap off for 15 minutes to get rid of any air bubbles....but about 5-10 minutes later the fluid just kept rising and rising until it started to overflow so I turned the engine off.

Any ideas on whats wrong?

 

You basicly have 2 posibilitys here:

A. It's leaking (onto the ground or hitting something hot and evaporating prior to hitting the ground.)
B. You have a blown head gasket (causing it to consume the coolant and probably burn it up prior to shooting it out the exhaust.)

check your oil, if you notice that it's milkey looking then you have a blown head gasket.


Check around the car for leaks comming from your coolant hoses.

There are only 4 MAIN coolant hoses
- to and from your radiator
- to and from your heater core (ports located at the firewall)

 

And don't forget about that coolant bypass hose. It allows coolant to bypass the rad when the thermostat is closed. I just replaced mine.

 

Ya its wierd...the coolant wasnt draining from the radiator when i was trying to do that air bubble thing

 

any idea why the coolant just rises and doesnt drain(when i let the car run with the cap off)? or is that normal?

 

it probably boiled over since it was not under pressure.

Boyle's Law

......temp, pressure and volume are directly related. Without the cap, pressure is not allowed to increase so volume must as temp does. Make sense??

It will also raise and lower normally just because it's getting pumped around through the engine. Usually not enough to spill over too much.