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Old 01-17-2017, 09:33 AM   #1
clee72
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Coolant Leak

I have been fighting a coolant leak around where the upper coolant hose connects to the expansion tank. It appears to be leaking around the small connection and not the big one. It leaks up to 16 fl oz over night especially on colder nights. I replaced the expansion tank and upper coolant hose this past weekend and it is still leaking. Has anyone ever seen this before? I haven't replaced the expansion tank cap yet but I don't see any signs of leakage above the tank connections.
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Old 01-17-2017, 10:55 AM   #2
white_335i
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Did you replace the exp tank cap? Could be leaking from there

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Old 01-17-2017, 10:57 AM   #3
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I have not but will try that today. I don't see any residue or moisture around it but it's a cheap thing to rule out

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Old 01-17-2017, 11:02 AM   #4
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If it is not the expansion tank cap, not sure what else could be leaking there. Are both the components OE? Did you check the Oring on the old hose that you pulled out?

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Last edited by white_335i; 01-17-2017 at 11:03 AM.
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Old 01-17-2017, 11:13 AM   #5
clee72
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The new tank is a Behr, the original came from BMW. The hose is not OEM but I have used the same brand on my other cars with success.

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Old 01-17-2017, 11:16 AM   #6
clee72
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The o ring on the old hose looked ok to me.

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Old 01-17-2017, 12:04 PM   #7
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O-rings can look OK but not be OK. So don't rely on how they look. Once you disturb any of them by removing a hose here or there you should replace the o-ring as a matter of course anyway. They will compression-set and not seal properly when you put them back. The o-ring at that connection is not doing its job and should be replaced. There is a guy on eBay that sells replacement o-rings for the cooling system by the username carniebert. $21 for all the o-rings in the system.


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Old 01-17-2017, 12:08 PM   #8
clee72
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As I stated in the original post, I replaced the tank and the upper coolant hose which would include the o rings. Do you think the new ones are faulty?

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Old 01-17-2017, 12:09 PM   #9
white_335i
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Originally Posted by clee72 View Post
I have not but will try that today. I don't see any residue or moisture around it but it's a cheap thing to rule out

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Food for thought. Go with a expansion tank cap from a E30. 1.4 bar vs 2 bar and read that the reduced pressure helps with the longetivity of the cooling system. I am running a 1.2 bar cap from G.A.S on my 330I and too soon to tell, but not adverse effects so far.

However, I am not totally convinced that the exp tank cap is the culprit. Did you say it leaks more after the car is parked and the system is cooled down or on a cooler day after the car ran?

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Old 01-17-2017, 12:09 PM   #10
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Thanks for the ebay info. That's a good price.

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Old 01-17-2017, 12:14 PM   #11
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You may have rolled the o-ring who knows. Use some silicone grease on it when you push it on next time. Also, to repeat what another poster said, it could be the cap. If so just match one from an o-ring kit that's a tiny amount thicker and replace the o-rings in the cap. That's what I did when my cap leaked out a little coolant on the side of the tank. I used an o-ring from the blue kit sold at Harbor Fright. Did the trick.
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Old 01-17-2017, 12:20 PM   #12
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I drive the car to work everyday. It sits overnight and when I start it up the next morning, the coolant light is on. The colder the night, the more it leaks. The temp has been in the 50's the past few nights and it has only leaked a little. Not enough to trigger the light but the top of the expansion tank is wet.

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Old 01-17-2017, 02:30 PM   #13
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Quote:
Originally Posted by clee72 View Post
I drive the car to work everyday. It sits overnight and when I start it up the next morning, the coolant light is on. The colder the night, the more it leaks. The temp has been in the 50's the past few nights and it has only leaked a little. Not enough to trigger the light but the top of the expansion tank is wet.

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Sounds like the O rings are shrinking when it gets cold.

I replaced cap and hose O rings and fixed my slow leaks. Def use silicone grease when re-installing.
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Old 01-17-2017, 04:07 PM   #14
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Check the coolant temp sensor o-ring in the lower radiator hose. Notorious for leaking while the car is sitting.
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Old 01-19-2017, 03:29 PM   #15
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Originally Posted by hitbyastick View Post
You may have rolled the o-ring who knows. Use some silicone grease on it when you push it on next time. Also, to repeat what another poster said, it could be the cap. If so just match one from an o-ring kit that's a tiny amount thicker and replace the o-rings in the cap. That's what I did when my cap leaked out a little coolant on the side of the tank. I used an o-ring from the blue kit sold at Harbor Fright. Did the trick.
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Old 06-12-2017, 09:03 PM   #16
clee72
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Just noticed I never reported back on this tread. I ended up replacing the upper coolant hose again and that fixed it. I guess the new one I purchased was defective. Thanks again for all the help and sorry for the late response.
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