[btwilson86]

Have you ever messed with the line going in and the line going out of the cap on your overflow? If so, you might have them backwards....

Basically what would happen is this: as your car heats up, pressure forces coolant into overflow through the tube that feeds to the bottom of the reservoir. As the car cools down, it'll suck the coolant back into the cooling system via that same hose.

If the lines are backwards, as the coolant expands it'll fill up the reservoir as it normally should. The problem is, it can't drink it back up cuz the line running from the radiator is not hooked up to that little hose that goes to the bottom of the reservoir. So the coolant will just sit in there.

Next time you drive the car, more coolant will try to go into the reservoir. Once it's full it's gonna go straight out that other line on the overflow cap, which is the purge line that goes straight to the ground, thus making it seem like an over-pressurized cooling system (like with a blown head gasket) when in reality it's just 2 hoses hooked up backwards.

That was alot longer than I thought it'll be, sorry for the ramble