Problems... =(
 

Yesterday when I was driving, my heat didn't work. I turned it up to 90 degrees and it was still blowing out cool air. Well when I stopped the car, steam/smoke was coming out of the hood, i opened the hood and the coolant was everywhere, so there's obviously a leak or a blown hose. Would this cause the heater not to work?

Car is at the dealer now. Had to get it towed last night. sucks. Hopefully CPO warranty will cover it...does anyone know?

That indeed could cause the heater not to work. The heater works off the heat of the engine coolant. Sounds like a hose blew. You need to trace down where it it leaking, repair the leak, then fill the system with coolant and bleed the system. Your heater should work again.

I've had my honda overheat before, then temp guage would go up, and people say to turn on the heater in your car to help take the heat off the engine so it won't get hot so fast.

But for the BMW, when I turned the heater on, it just blew cool air...so that's what I didn't understand...

Thats because there was no coolant in the heater core to heat up the air! You have a coolant leak somewhere. Fix it before driving the car again.

Absolutely... you've leaked out enough coolant to where it won't circulate through the heater core. On an overheating engine, turning on the heater gives it another 'outlet' to dishcarge the heat... but this presumes the car is overheating for another reason other than lack of coolant. The heater core lines on most vehicles pick off the upper part of the engine's coolant system, so it is the first to loose it's functionality when you loose coolant. You must have caught it right as you sprung your leak, since the low coolant sensor hasn't been triggered.

Actually the low coolant sensor did trigger, but the car had to be turned off and on again before it gave the error message in the OBC display...

I am having the same problem with my heater. I have replaced the radiator, all the coolant hoses, thermostat, water pump, etc. Any suggestions?

If there is a clog in one of the heater core lines, or in the heater core itself, then you won't get any heat. Just for clarification, the way it works is by taking a 'pick off' of engine coolant; two lines (one in and one out from somewhere on the engine) pass hot coolant through a little mini radiator called a 'core' (basically a heat exchanger). Your blower fan then blows air through the radiator, therefore picking up the heat from it. If you don't get any flow through your heater core, you don't get hot engine coolant, and you don't heat your little heater radiator... thus blowing cold air. This is why you don't get any heat when you just start your car. Your engine needs to warm up before if can heat the heater core.

The flappers / control unit that controls the heat may not be working either...

Both are a supreme pain in the butt to get to...

-Wayne