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Discussion Starter · #1 ·
Hi, I'm a newbie and I've read through so many posts but none seem to nail my issue...
My 2000 323i (E46) runs like a top, but I have a strange heating issue:

Begin with a cold start (car has been off overnight, for example), and the heat comes on as it should, nice and warm.
Ride around, typically I do a lot of highway, but it seems not to matter if I'm at any consistent speeds: Heat SUDDENLY blows COOL, and stays that way forever and ever amen. EVEN if I shut the ignition off, and let it sit for even an hour (say)... the heat still blows cool.

I'd have to wait for a cold-start condition again, and then it's fine again... until it happens again.. and it happens ALWAYS with the above scenario. There is never a time when it continues to blow hot after even a half-hour of driving. After a half-hour or so, the cool air starts again.

NOW, at some point I used to flip the defroster on, and occasionally I'd notice the heat would SLOWLY come back through that system, and I'd flip it back to the floor (or middle) vents. It no longer will do that (at least, I've given it an inordinately long time to do so but so far even after several to 10 minutes, no success.

I have had the heater core replaced (other issues), the radiator, the thermostat, and the water pump as well! Still no difference.

My next step is to replace the module, which I just bought and am waiting for to get here.

Anyone have a clue?!?
 

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catso
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3,163 Posts
Hi, I'm a newbie and I've read through so many posts but none seem to nail my issue...
My 2000 323i (E46) runs like a top, but I have a strange heating issue:

Begin with a cold start (car has been off overnight, for example), and the heat comes on as it should, nice and warm.
Ride around, typically I do a lot of highway, but it seems not to matter if I'm at any consistent speeds: Heat SUDDENLY blows COOL, and stays that way forever and ever amen. EVEN if I shut the ignition off, and let it sit for even an hour (say)... the heat still blows cool.

I'd have to wait for a cold-start condition again, and then it's fine again... until it happens again.. and it happens ALWAYS with the above scenario. There is never a time when it continues to blow hot after even a half-hour of driving. After a half-hour or so, the cool air starts again.

NOW, at some point I used to flip the defroster on, and occasionally I'd notice the heat would SLOWLY come back through that system, and I'd flip it back to the floor (or middle) vents. It no longer will do that (at least, I've given it an inordinately long time to do so but so far even after several to 10 minutes, no success.

I have had the heater core replaced (other issues), the radiator, the thermostat, and the water pump as well! Still no difference.

My next step is to replace the module, which I just bought and am waiting for to get here.

Anyone have a clue?!?
Did you bleed the cooling system properly? Maybe you have an air pocket in there. It helps to do it with the front end slightly higher than the rear. Sometimes you have to do it more than once to get all the air out.
 

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War Damn Eagle
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It sounds to me like a thermostat issue? Sounds like at cold start, it's closed, creating the heat needed. Then after it opens up, it stays open not allowing it to creat the heat needed. Then after it cools and closes, it will have warm air again till it opens up........ Did you replace it with and oem temp range thermostat or something to make it run cooler?
 

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Maybe on the air pocket and maybe on the thermostat...... I'll venture a guess and sayit could be the heater water valve that routes water to the core. On my 330 it's mounted to the frame/strut tower under the intake tube/manifold connection.... has a couple 1 inch hoses going to/from it and is about the size and shape of two "C" batteries, IIRC. Either way, look for the hose that goes through the firewall and you can trace back to the valve.

Maybe try feeling the difference in temperature on the two hoses next time you get it up to operating temp with the heat set to "on" in the cabin. If one hose is hot and one is not then that's likely your culprit.

I'm thinking that even with a stuck open thermostat, the coolant would still get hot enough to provide heat.
 

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Discussion Starter · #5 ·
I've had it bled several times.. of course, it's possible that each time, it wasn't done right, but I kind of think that possibility has been exhausted!
 

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Discussion Starter · #6 ·
Regarding the thermostat, I'm going to have that replaced as well... only lately has it been seeming to stick open (on the highway the temp gauge seems to be hovering left of center more than usual - but that's only a recent thing).
 

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Discussion Starter · #7 · (Edited)
Sorry about the mis-replies... I'll get the hang of it...

I wasn't aware of "heater water valve"! I'll have that checked as well... hopefully they don't have to pull the dash off to check it!
I'll also look into the temp difference of the hoses...
Winter is coming, I gotta get this thing figured out!

Thanks everyone!
J
 

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I had this exact problem. Ended up being the climate control fan. Problem it created was the heater would only work for a very short while and then it would blow cold air no matter what. And before that happened we could smell the slight smell of what was a burnt smelled like an overheating engine but was instead a toasted climate control fan. We got a used one for $150 and it's worked perfect ever since.
 

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Discussion Starter · #9 ·
The FAN? That is so strange, because it still BLOWS air... when you say it was the "fan", does that imply some other element integrated WITH the fan?? You see why I'm confused? :))
 

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If you have climate control there is a fan that sucks the air into the vent sensors at the top by the sunroof controls, at the stereo, and down below. That's how it controls the air mixture and fan speed when it's at auto and stuff. Fan goes out, it has no idea what to blow.
 

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Discussion Starter · #11 ·
OK, thank you... I almost always run it on "manual", rather than auto (wonder if that negates the "need" for that function you are describing...) But I will check it out and post my result!
 

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catso
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I had this exact problem. Ended up being the climate control fan. Problem it created was the heater would only work for a very short while and then it would blow cold air no matter what. And before that happened we could smell the slight smell of what was a burnt smelled like an overheating engine but was instead a toasted climate control fan. We got a used one for $150 and it's worked perfect ever since.
Where is this fan located?:confused:
 

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I think its behind the climate control center. Should be on the end of the vent tubes if you follow it in. I'll try to find a pic.
edit:
Might be in the unit. I didnt replace it cause I was out of town and the wife brought it in to the BMW repair shop and that's what they said thy did.
 
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