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Driveline, Engine & DME Tuning
Talk about driveline improvements, NA tuning and DME tuning your E46 BMW here. This includes diffs, intakes, exhausts, chips, software and OBD tuning.

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Old 03-17-2010, 02:00 PM   #1
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Cool Expansion tank Problem/Solution???

I also have had tank woes. Just bought the car and it was low on coolant. Added coolant and noticed fluid around the top of the tank. At first i assumed it was a crack along the top seam or the cap. So i ordered a new tank and cap. Replaced that and filled her back up with coolant (trying to be very careful about over filling). A few hundred miles later my light comes on again, coolant showing in the same spots, doesnt appear to be from the cap, it appears to be from the seam along the top where the top piece connects with the lower part of the tank.
What i dont understand is that if there is a failure at the top of the tank that means that the level of coolant under operation is near the very top. Thus even if i had a rock solid tank it would build up so much pressure that it would explode.

1: Same failure in the same spot on both tanks.
2: Failure somewhere else in the system such that the coolant level under operation is abnormally high, and i just got lucky that it cracked at the top.
3: I am missing something that would cause a de de deeee moment.

1: Take the first tank and reinforce it with fiberglass, dont want to keep buying these things forever.
2: Poke around in the beautiful spring weather under the hood and see if maybe i left the pressure release valve open, test with cap on tight, at temp...... ect
3: Have another beer and read everyones criticisms

Please let me know what you guys think.
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Old 03-17-2010, 11:49 PM   #2
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2. When the engine overheats, it blows coolant out of the system. The first place it it runs to is that seam. It's a great shelf for coolant.
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Old 03-18-2010, 02:44 AM   #3
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I'm not sure how well hand laid FG would bond or if it would even provide any extra strength. I think your best approach is replacement as preventive maintenace every 60k miles.

Or buy the aluminum radiator and expansion tank from Zionsville Autosport for $1300.
2013 F30 328i - Melbourne Red
2011 E90 M3 - Monte Carlo Blue
2004 E46 M3 - Imola red
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Old 03-19-2010, 09:21 AM   #4
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The engine is not overheating, even after i let the light be on for a few days, gauge is still solid dead center. After testing my old tank overnight in the garage for the smallest of leaks i was unable to get any water to come out. I read somewhere on here that the cap is rated for 2 psi. What im thinking is that my tank is functioning properly and the cap is functioning properly and venting. Or the Steam/fluid coming out of the seam is getting above the seam just under the cap.
That would mean that there is something causing excessive coolant to be in the tank under enough pressure to reach the cap.

Air in system (air expands alot more than fluid)
Some clogged return??

I have tried two ways to bleed the system. One cold, one hot. When cold turn key to pos 2, turn heat all the way up, vent valve near tank, add coolant until bubbles stop. When hot same procedure. Got no bubbles when cold, got about 2 seconds of bubbles when hot.

I really hope that someone else has had this problem and was able to find a solution.

I must add that i am not using BMW coolant until i find a solution. Just occurred to me that maybe the coolant im using has a much lower boiling temp. Any thoughts.

Last edited by florida2002m3; 03-19-2010 at 09:34 AM.
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Old 03-19-2010, 09:43 AM   #5
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Does any smoke come out of your exhaust? My first thought reading this was a potential head gasket problem.
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Old 03-19-2010, 10:09 AM   #6
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No smoke, and i can see that the coolant is coming out of the top of the expansion tank, either from the seam or from the cap.
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