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General E46 Forum
This is the place to get answers, opinions and everything you need related to your E46 (sedan, coupe, convertible and wagon) BMW!

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Old 12-09-2012, 12:04 PM   #1
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Join Date: Dec 2012
Location: Arlington
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My Ride: 2000 323i
2000 323i Radiator/Tank Issues

Hey All-

First time posting something, but I'm having a major issue with my 323i radiator tank. A few weeks ago I was driving home and noticed my radiator light come on and my gauge shoot straight to red. I pulled over put some water in it, but the tank had a huge split down the side. So I had my car towed.

I ordered a new tank, but when I replaced it, used the same cap, and I noticed some broken plastic pieces fell out. I'm assuming this was just part of the inside of the old tank. I filled up the new tank, tightened the venting screw, and turned the car on with the heat blasting. Around the time the car gets to normal temperature steam starts shooting out the venting screw and the cap of the tank. I loosen the screw, but I continue to get steam shooting out of it for a few minutes. I then noticed that the tank is heavily leaking fluid out the bottom. I'm assuming that pressure is just building up and forcing the fluid out. Am I right? This even happens when I take the venting screw completely off.

I need some help knowing if I'm doing something wrong or if I need to replace something else.

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Old 12-09-2012, 12:14 PM   #2
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Join Date: Mar 2010
Location: Dallas, TX (USA)
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First, do Not reuse old plastic parts from failed component(s). Always get a new cap with new expansion tank.
2. Do you have an manual or automatic?
3. What brand of expansion tank did you purchase (or where did you buy it)?

Lastly, did you remember to bleed the cooling system immediately after your exp.tank replacement? This step is critical and must be done properly to prevent random overheating problems.

DO NOT drive your vehicle in this state currently.
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Old 12-09-2012, 12:32 PM   #3
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Location: Arlington
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Thanks for the quick reply!

It's an automatic. The tank is a Behr that I bought from bavauto.com. I'm assuming that I should purchase the Behr cap to start with, huh? Or should I just fork over the extra money and purchase the official BMW tank and cap?

I bled the system by letting the fluid drain from the bottom where the blue screw is located. Is there anything else that I need to do to bleed it?
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Old 12-09-2012, 12:40 PM   #4
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I'm a little concerned with the fluid coming out of the bottom of the expansion tank, it leads me to believe that you didn't properly seat the new tank in the housing... Please make sure that the new tank is seated in the housing and that the clip that holds it in place is holding the new tank.
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Old 12-09-2012, 12:47 PM   #5
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it too sounds to me the new expansion tank is not seated to the lower radiator connection fully.
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Old 12-09-2012, 01:03 PM   #6
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I'll double check the seal on the bottom of the tank. I did look at where its leaking though and its coming from where the fluid level sender is located on the bottom. So I'm not sure if there's too much pressure in the tank and that may be a pressure release point? I've heard that if there's too much fluid in the tank that the tank will leak at certain points like that.
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Old 12-09-2012, 04:16 PM   #7
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Most likely it'll be coming from the connection for the trans thermostat. This is also a common point for leaks when the t-stat is not replaced.

The level sensor does not sit directly in coolant, it is a reed switch with a floating magnet inside the tank.

When you are seating the ET, make sure the spring clip on the bottom of the tank is pulled out before you seat the tank. This is also a bit easier with a small amount of coolant on the o-rings to lubricate them.

When you are bleeding the system, the bleed screw is removed with the heat to maximum, the fan at the lowest setting with the key in the on position and the engine off. Add coolant until it comes out the bleed screw with zero air bubbles. Once you have this, remove the extra coolant from the ET until the level is correct.

The blue screw you refer to is for draining only. This is not used to bleed the system.
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