I was driving my 2002 325i yesterday and the coolant light came on. I didn't have time to go get coolant right away so i waited until today to put coolant in it, about an entire bottle. I thought that was the end of it, but Iwas driving about 10 minutes later when I noticed my engine was overheating and i had steam pouring out from under my hood. The steam was coming from a little hole in the tube that runs from where you put coolant in, and I'm assuming there used to be a screw or something there. I put about another bottle and a half of coolant in and drove the car home, and AAA is coming to tow it to the BMW dealership tomorrow to fix it. Anyone know what went wrong and why it happened? Hopefully I don't have a blown headgasket or a warped head.

Sounds like your bleed screw is missing. :confused

It could be a bunch of things, but it sounds like some sort of leak obviously, so I wouldn't worry too much. The damage issue is a wait and see thing.

yeah sounds like the bleed screw, if you didnt overheat your engine too bad, then it should be a cheap fix. you cannot just buy that plastic screw tho, you have to replace the whole radiator hose, about $25, but still a cheap and easy fix. make sure you bleed the system after you refill

You can buy the plastic screw. Take a picture, then we can give you an answer possibly.

+1 on the bleed screw

cheap ass radiator expansion is a weak point in the coolant system

I had the tank go out, fixed it then a week later bleeder screw! just to be on the safe side I baught two bleeder screws, was only a couple dollars and the spare? in the glove box :buttrock

yeah sounds like the bleed screw, if you didnt overheat your engine too bad, then it should be a cheap fix. you cannot just buy that plastic screw tho, you have to replace the whole radiator hose, about $25, but still a cheap and easy fix. make sure you bleed the system after you refill


-1

Bleed screw is part number 17111712788 (up to 10/2003) or 11537793373 (after 10/2003). They're plastic and they crack easily if overtightened.

What would cause the build up of gasses to blow the the screw out?

I would think if there was excessive pressure in the system (like from a blown head gasket) the hose would blow before the bleeder screw. Hopefully it just came out and that's the end of it. If you spent any time driving the car with the temp in the red, you very well could have warped your head. Do a search on bleeding the cooling system and top it off and drive it. Keep an eye on that temp gauge. If it starts to move from dead center, pull over and cut the engine. Keep a gallon of coolant with you and a skinny funnel so you can top off on the side of the road just in case.

It's a sealed system that is under pressure any time the engine is hot. The coolant and air expand (or attempt to) as they heats, causing an increase in pressure. PV=nRT remember?

I've read that the pressure is highest shortly after the engine is shut off. This makes sense since the heat of the engine block is still transferring into the coolant, but the water pump and radiator aren't dissipating that heat into the environment like they do while the engine is running.

And, if the plastic bleed screw is already cracked due to overtightening/age/abuse, then it'll easily split down the middle when it's subjected to pressure.