What causes coolant dump?

You guys know how the ressivour for the antifreeze/coolant has two tubes. one leads to the thermostant housing and the other is the overflow dump. well to day my car dumped some coolant when I got to work. its never done that before. I had flushed the system over a year ago and never dumped on me, today I get to work and see a splash under my car, figured the radiator got busted but no, its the dump tube.
So what exactly causes the ressivour to overflow? Im not sure if I should take this as a bad sign or if its perfectly normanl and I have an AutoX tomorrow!

strange...was ur car running hot at all? maybe somehow you just got some air in the system and it displaced some coolant...ive had that happen on my chrysler b4...

no, it didnt overheat. I didnt give it time to warm up which i usually do but I didnt run it hard at all.

My dads truck was blowing antifreeze out he overflow. It wasnt overheating either. He had a cracked head.:eek:

damn it! you had to say that :banghead: now Im scared.

could be overheating, could be bad head gasket, could be a lot of things.

My car used to do it every once in a while, but nothin was wrong with it......I never did figure out why.

no, it didnt overheat. I didnt give it time to warm up which i usually do but I didnt run it hard at all.

maybe its because you didnt let the thermostat open up...but i dont see why it would overflow, unless somethings pressurizing the system...hmmm

well, if its anything serious (cracked head, blown gasket, etc) it will happen again, so i wouldnt worry about it for now man.

i had a thermostat gimme that problem before

Stealthee could be right, either it's just a freak accident, or there is compression leaking, which might mean your head is either warped or cracke (highly unlikely though).

To check, open the coolant top, first check if there is any oil, if there is, OUCH, heads gone, but to make sure there is no compression leak, fill the coolant level, then have someone start the car and leave the top off, and look, if the coolant bubles, or level starts raising, there is compression leaking, and you might want to get that fixed.

You know, I also had a coolant dump 2 winters ago. I filled it back up to normal, and never had a problem with it again. No leaks, no head gasket leaks, no overheating. No problems since.