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I Just bought a 99' 323i two weeks ago and I love the car, but out of nowhere the car overheated. I thought it might be the water pump or the thermostat so I replaced them both. When I took the water pump out it was shredded, the plastic impellers didn't make it. I figured that would be the cause of the overheat. I also replaced the upper and lower hoses, the auxiliary fan, and the coolant temp sensor. Oh I also drained the old coolant out and put new coolant in and bled the system as well. It's still doing the same thing as before only it doesn't overheat quite as fast. It doesn't blow out any hot air when I have the heat on full blast and if i put the A/C on cold it only blows out the driver's side and then the car overheats real fast. I don't know where to look next and was hoping someone could point me in the right direction before I'm forced to take it to the dealer and get back doored from them. Any help would be greatly appreciated. Thanks again.
 

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Are you 10,000% sure there's no air trapped in the system? It sounds like you've got an air pocket trapped in the heater core, which would explain both the lack of heat through the vents and the overheating.

Search the forum for how to completely bleed your cooling system.
 

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i'm not 100% sure, but from what I've been reading and your input that's what i'm gonna lean towards. Tomorrow I'm gonna drain the coolant out and do it again. Thanks for your advice.
 

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Tomorrow I'm gonna drain the coolant out and do it again. Thanks for your advice.
You don't have to drain out the coolant to bleed the system. On my last coolant change, I had to crack the bleeder and top off the expansion tank a good 3 or 4 times each before all the air was purged. It will help to park the car on a slight incline so that the expansion tank is at the highest point of the system (which is where all the air pockets will naturally try to accumulate).

Also make sure that your heater is set to the hottest setting (with the key on, engine off) to allow coolant to pass through the heater core in the first place.
 

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You don't have to drain out the coolant to bleed the system. On my last coolant change, I had to crack the bleeder and top off the expansion tank a good 3 or 4 times each before all the air was purged. It will help to park the car on a slight incline so that the expansion tank is at the highest point of the system (which is where all the air pockets will naturally try to accumulate).

Also make sure that your heater is set to the hottest setting (with the key on, engine off) to allow coolant to pass through the heater core in the first place.
Yes, bleeding of air was not done properly if you aren't getting hot air out of the heater. Follow process above. You dont have to do 3-4 times but on first drive around the block after bleeding, leave heater on to max hot setting and it will self-remove SMALL residual air bubbles by itself.
 

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okay so i bled the system multiple times and still does the same thing. And when it starts to overheat and i shut it off, it sounds like the water is boiling in the upper hose and when i squeeze the hose with the bleeder screw open a bunch of air comes out. So i don't know where to go from here. I've already let it cool down and topped it off and bled it again and still the same thing is happening. The only thing I haven't replaced is the expansion tank, could that be it? Well I'm pretty new with BMW's so I don't know what else to do, but take it to the shop.
 

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pieces from the old water pump stuck somewhere?

Did you keep all pieces you pulled out to see if something was missing?
 

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okay so i bled the system multiple times and still does the same thing. And when it starts to overheat and i shut it off, it sounds like the water is boiling in the upper hose and when i squeeze the hose with the bleeder screw open a bunch of air comes out.
If you properly bled the system, there wouldn't be any air to squeeze out. There are literally 4 simple steps to doing this.

1) Park on a slight incline.
2) Turn the key to the accessory position and set the heater as high as it'll go (but set the fan speed to low).
3) Remove the coolant cap AND the bleeder valve, and slowly pour coolant into the reservoir until absolutely, positively NO bubbles are coming out of the bleeder hole. It is NOT enough to simply "fill" the reservoir. You need to continue pouring in coolant so that it "overflows" through the upper radiator hose and throughout the rest of the cooling system. I suspect this might be where you went awry.
4) Repeatedly drive the car up to operating temp and crack the bleeder valve until you stop hearing air hiss out. Keep the coolant topped off while doing so.
 

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Discussion Starter #9
Thank you SteveX82 I will try to do it again. Question? Do I keep the key turned on to the 2nd position while I'm filling it up? Thanx again.
 
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