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      08-05-2020, 10:00 PM   #1
shaanfx
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Coolant spewing from expansion tank cap

Picked up a used 2005 Z4 3.0i recently and got some things fixed on it, including replacing the coolant expansion tank. Ever since then, whenever I go on a spirited drive I find several drops of coolant to the right of the cap (see pic) and on the underside of the hood. Took it back to my indy who said it just "burped", he re-bled the system, said it wasn't initially wanting to bleed but he got it done, topped it off and said I should be good to go. Well I drive 7 miles and same thing again. Next thing he wants to try is changing the cap. Is this something any of you have seen before? Is it likely to be the cap or something else? No other issues seen besides the coolant leaking from the cap.
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      08-05-2020, 11:06 PM   #2
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Maybe you need a new cap or there's too much coolant in the system. It happened to my Z4 when I first bought it and it was spilling green coolant. I bought blue coolant ASAP and flushed the system.

Last edited by T-Bears; 08-05-2020 at 11:29 PM..
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      08-06-2020, 08:44 AM   #3
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Might be, when i redid my hoses, I replace the cap.. it was like 15 bucks..

I dont remember, does 2005 have electrical pump too ? Theres a procedure to properly put the right amount of coolant in, I'm not sure if later year procedure applied to the 2005 one.
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      08-06-2020, 01:04 PM   #4
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Did you change the hose to the expansion tank? Could be that it isn't quite sealing tightly enough. I had leakage from there prior to my changing the expansion tank. Took it off... cleaned the connection of any crud/deposits and then applied a light film of silicone to "grease" the o-rings. Never had a problem with coolant leakage after that.
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      08-06-2020, 08:47 PM   #5
shaanfx
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Thanks so much everyone for your insight. I replaced the cap today and went on a quick but hard drive. No spewing! Cautiously optimistic replacing the cap fixed the issue, although today's weather was about 25 F cooler. I'll keep an eye on it and keep you all posted.

By the way, does this look like it's full but not over full? The diagram is a tad cryptic to me, as I'm not sure what it considers to be the "top" that the bobber protrudes past. This is with the car stone cold.
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      08-06-2020, 08:52 PM   #6
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Quote:
Originally Posted by shaanfx View Post
Thanks so much everyone for your insight. I replaced the cap today and went on a quick but hard drive. No spewing! Cautiously optimistic replacing the cap fixed the issue, although today's weather was about 25 F cooler. I'll keep an eye on it and keep you all posted.

By the way, does this look like it's full but not over full? The diagram is a tad cryptic to me, as I'm not sure what it considers to be the "top" that the bobber protrudes past. This is with the car stone cold.
That looks too full to me, you shouldn't be seeing the second bubble on the stick..
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      08-14-2020, 09:59 PM   #7
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Update - since replacing the cap, haven't seen the spewing issues return Guess it's a good idea if you're replacing the reservoir to do the cap also. Honestly surprised they didn't just originally do it by default!
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      08-15-2020, 07:44 AM   #8
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Many BMW experts recommend filling only to the minimum level, cold, so the top of the float is level with the top of the threads. Leave a little room for hot fluid to expand. BMW's plastic tanks have a history of rupturing, an issue exacerbated by overfilling.
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      08-15-2020, 08:35 AM   #9
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Quote:
Originally Posted by jhm5 View Post
Many BMW experts recommend filling only to the minimum level, cold, so the top of the float is level with the top of the threads. Leave a little room for hot fluid to expand. BMW's plastic tanks have a history of rupturing, an issue exacerbated by overfilling.
What's the easiest way to remove a little fluid? Take off cap and use turkey baster?
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      08-15-2020, 02:31 PM   #10
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Yes, or drain from bottom, the blue plug.. loosen it a little and catch it... Both easy
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