I have a 1993 525i and was on my way home today and my hot air went cold....I also noticed steam and coolant spewing out of a vent hole on top of the expansion tank attached to the radiator, which baffled me. So I did what any normal person would have done and got a new thermostat and gasket and replaced the thermo and gasket according to BMWe34.net, read about bleeding the system and tried my best to bleed the system using the bleed screw at the lower end of the expansion tank....well, now I have hot air and the temp is ok on the car, but steam and coolant keep spewing out of the top of the expansion tank....

So my question is....Is something else wrong? Did I not do something correctly?

Could be a cracked expansion tank or a bad cap. On a 93 I'd bet on it being a failed expansion tank. When you replace it do the radiator also. 14 year old plastic is usually pretty brittle.

Well the radiator cap was completely shot....never even thought of that. So I replaced the cap thinking that was the problem....well it's not. I am thinking the pressure relief valve on the expansion tank is bad....

If I squeeze the main upper coolant hose that goes to the thermostat housing I hear the air escaping out and back in the pressure fitting where the steam and coolant is coming from....I am assuming I should not be able to do this considering the system should be under pressure....