Expansion Tank Leaking

Kev7274 · 11-02-2017, 07:45 PM

Went outside today and noticed antifreeze on the ground. Reservoir wasn't completely empty.

I know that the expansion tank is leaking because I can see it coming out of the
weld area that joins the two pieces together. I also believe it's leaking from the bleeder screw dut to there being antifreeze on the little lip above that weld seam.

I have included photos of what it looked like under the hood and want to know if the leaking from the weld seal between the two parts would cause the kind of spray in the engine bay due to the heat and pressure in the expansion tank.

Take a look and tell me what you think.

Kev7274 · 11-02-2017, 07:49 PM

320IN54 · 11-02-2017, 08:08 PM

I am not too sure about the actual reason for this but I experienced the same thing when my water pump went out. My coolant started to overheat and boil causing the pressure to build up in the expansion tank and making leak at both the welds and screw. I swapped everything out and no problems since. Not much to go off of but it gives you an idea as what the problem might be

Kev7274 · 11-02-2017, 08:23 PM

Thanks. I've not noticed any issues with overheating so I hope it's just a leaking tank.

Quote:

Originally Posted by GotPwned

I am not too sure about the actual reason for this but I experienced the same thing when my water pump went out. My coolant started to overheat and boil causing the pressure to build up in the expansion tank and making leak at both the welds and screw. I swapped everything out and no problems since. Not much to go off of but it gives you an idea as what the problem might be

The Nightman · 11-03-2017, 01:14 AM

Is your coolant overfilled?

Boland01 · 11-03-2017, 08:49 AM

Time to buy a new overflow tank, Same thing happened on our 2007 335i. From the continued heat cool cycles the expansion tank on ours also split at the seam. Good news are new ones are pretty cheap.

BeastMode335i · 11-03-2017, 11:14 AM

URO has one for like $35 on eBay, been using it over a year with no problems.. Make sure to get the URO cap as well, since BMW decided to change part #'s and the old caps don't thread properly on the new expansion tanks.

lab_rat · 11-03-2017, 03:36 PM

Often it's the rubber o-ring gasket on the cap & expansion valve that ends up causing the leaks...not the tank itself. Try replacing the cap & valve first, and if that doesn't solve it, then you know you have to replace the tank.

I replaced the cap and valve and my small leaks were gone.

When I compared the rubber o-rings on new vs. old, and sure enough, the old rings were flattened and were very hardened when compared to the new ones.

Kev7274 · 11-03-2017, 04:04 PM

Thanks for the input,I appreciate it.

EB89 · 11-05-2017, 02:36 AM

The expansion tank cracking along the plastic weld is common, replace the tank.

It’s a 5 min job.

11-02-2017, 07:45 PM	#1
Kev7274 Private First Class 18 Rep 123 Posts Drives: 2009 335i Join Date: May 2014 Location: United States iTrader: (2)	Expansion Tank Leaking Went outside today and noticed antifreeze on the ground. Reservoir wasn't completely empty. I know that the expansion tank is leaking because I can see it coming out of the weld area that joins the two pieces together. I also believe it's leaking from the bleeder screw dut to there being antifreeze on the little lip above that weld seam. I have included photos of what it looked like under the hood and want to know if the leaking from the weld seal between the two parts would cause the kind of spray in the engine bay due to the heat and pressure in the expansion tank. Take a look and tell me what you think.
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11-02-2017, 07:49 PM	#2
Kev7274 Private First Class 18 Rep 123 Posts Drives: 2009 335i Join Date: May 2014 Location: United States iTrader: (2)
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11-02-2017, 08:08 PM	#3
320IN54 First Lieutenant 123 Rep 331 Posts Drives: 2007 BMW 335i, 2021 BMW M2C Join Date: Jan 2017 Location: Irvine iTrader: (0)	I am not too sure about the actual reason for this but I experienced the same thing when my water pump went out. My coolant started to overheat and boil causing the pressure to build up in the expansion tank and making leak at both the welds and screw. I swapped everything out and no problems since. Not much to go off of but it gives you an idea as what the problem might be
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11-03-2017, 01:14 AM	#5
The Nightman Cometh 1090 Rep 1,308 Posts Drives: Boy's Soul Join Date: Jul 2016 Location: Boy's Hole iTrader: (4) Garage List E90 LCI "330i& ... [10.00]	Is your coolant overfilled?
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11-03-2017, 08:49 AM	#6
Boland01 Lieutenant 151 Rep 460 Posts Drives: 2010 535ix, 2008, 2007 335i Join Date: Sep 2013 Location: Magnolia, TX iTrader: (0)	Time to buy a new overflow tank, Same thing happened on our 2007 335i. From the continued heat cool cycles the expansion tank on ours also split at the seam. Good news are new ones are pretty cheap.
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11-03-2017, 11:14 AM	#7
BeastMode335i Maximus Decimus Meridius 1130 Rep 4,584 Posts Drives: F30 335i Join Date: Apr 2014 Location: Down South iTrader: (2)	URO has one for like $35 on eBay, been using it over a year with no problems.. Make sure to get the URO cap as well, since BMW decided to change part #'s and the old caps don't thread properly on the new expansion tanks. __________________ F30 335i Melbourne Red Metallic M-Sport Package
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11-03-2017, 04:04 PM	#9
Kev7274 Private First Class 18 Rep 123 Posts Drives: 2009 335i Join Date: May 2014 Location: United States iTrader: (2)	Thanks for the input,I appreciate it.
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11-05-2017, 02:36 AM	#10
EB89 Brigadier General 541 Rep 3,131 Posts Drives: 2011 335i e92 DCT Join Date: Sep 2015 Location: Australia, NSW iTrader: (0) Garage List 2011 BMW 335i e92 [0.00]	The expansion tank cracking along the plastic weld is common, replace the tank. It’s a 5 min job.
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