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Discussion Starter · #1 ·
'04 330i, 105k miles. Coolant light comes on once car is warmed up and at speed. Usually goes out after a minute or two of idling, then comes on again at speed. The most recent cooling system work was a new water pump about 3 months/4k miles ago...topped system up with BMW coolant mix then, no problems until now. Coolant level is fine. Temp gauge is normal. Replaced ET cap (cheap shot in the dark), but same results. Anyone experienced similar problem? Any ideas? Thanks!
 

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2016 340i xD 6-spd
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I'm sure others have experienced this, but good luck finding the threads! Maybe someone will stop by, otherwise I'll just toss out a few ideas for you.

One--assume your coolant level isn't fine. Check the dipstick in the a.m. on level ground.
Two--the temp level sensor is easily replaced if need be. It's in a dry part of the ET. 90 degrees to one way to unclip after you've removed electric connector.

Three--this sensor is identical to the level sensor on the windshield reservoir. Not sure where it is; haven't pulled mine yet...anyway, you can easily swap to test if need be.

Four--your dipstick might just be stuck. It might have gotten low too many times, gunk built up where it's supposed to slide freely. Check it's function carefully when you check in the a.m. I don't think your level is fine, but if it is, then swap/replace sensor and check wiring heading back from the connector. Clean with electric cleaner according to label instructions--

Five--you'd naturally seep some coolant from some places. Clean things up while you're there, keeping an eye out for tell tale residue.

Six--don't ignore cooling system. Now you should monitor the level manually carefully and properly until you get this sorted out. If you're losing coolant and not seeing leaks, start reading fanatics a lot more...use advanced/title search.

BTW, I've never seen an Arctic Mallard. Photo of one or Marissa please? I guess you like these ducks an awful lot, huh? Me? I enjoy watching the hawk migration, but that's another story, I don't get emotionally involved with them too much, you know.

Oh, sorry, forgot you've only got three posts! Marissa will do on her own!
 

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Have you checked under your radiator? (preferably with the plastic splash plate removed.) Look closely around the side(S) of the expansion tank with a flashlight for leakage/coolant-residue.
Because, from your description it sounds like a leak > Very likely one of those famous "hairline" cracks on the ET.
 

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Discussion Starter · #4 ·
ET and level sensor on order. No outright evidence of failure, but from what I've read over the years, it's not a matter of if the ET will fail, but when, so I might as well just put in a new one by the time I take it out for a thorough inspection...probably should have replaced it when the first water pump went...or the second...
 

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i had a simular problem recently and as was recommended to me to bleed the air out of the system, and it worked. i found that the light would come on shortly after i turned the heater on.. when i was at a stop or idle it would go off and back on after speeding up.. was a very simple fix and light hasnt come back on since..
 

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'04 330i, 105k miles. Coolant light comes on once car is warmed up and at speed. Usually goes out after a minute or two of idling, then comes on again at speed. The most recent cooling system work was a new water pump about 3 months/4k miles ago...topped system up with BMW coolant mix then, no problems until now. Coolant level is fine. Temp gauge is normal. Replaced ET cap (cheap shot in the dark), but same results. Anyone experienced similar problem? Any ideas? Thanks!
I just started having the exact same problem... my level is fine too. I replaced my whole system last summer and I haven't had any problems until now. Far as I can tell I have no leaks, let us know what happens. But I do have one more problem that seems to be accompanying this, my heat isn't working at idle. I notice know that the car is blowing cold air at stop lights??
 

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I had the same issue, and was almost positive that I had enough coolant.
try this. my cooling system was recently done as well and was filled with BMW coolant. Anyways, open the cap, loosen the bleeder screw(i had a lot of air come out), see how high the dipstick goes. Mine went past the cap. Maybe you have a lot of air trapped.
 

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level sensor in the ET failed. The cheap plastic hinges for the sensor (rod) worn out through time, gave up eventually. Replace the whole unit.
 

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Discussion Starter · #9 ·
It turned out I did have a small, slow leak from one of the lower coolant hose fittings where it met the ET. I purchased Pelican's hose set and replaced all three that connect to the ET. I'll replace the rest when I do the annual Spring maintenance. Thanks for all the input!
 

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It turned out I did have a small, slow leak from one of the lower coolant hose fittings where it met the ET. I purchased Pelican's hose set and replaced all three that connect to the ET. I'll replace the rest when I do the annual Spring maintenance. Thanks for all the input!
So, you had a Low Coolant warning AND low coolant due to a leak? Correct me if I am wrong, but that's how it's supposed to work.
 

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Discussion Starter · #11 ·
So, you had a Low Coolant warning AND low coolant due to a leak? Correct me if I am wrong, but that's how it's supposed to work.
I guess you're right, jdsmartA$$..er, strickland...at least the light got my attention. I'm puzzled by your comment though...who the heck ever said that wasn't how it was supposed to work? Since the light came on only at speed, and the level checked fine when cold (you know, remove pressure cap, level float right in range, and moving freely) the problem wasn't readily apparent. So...a very small leak it must have been; and a bit of a PIA to track down since it was so small and so much has to be removed for a good look. Even once completely removed, there is no visual indication of any defect in the old hoses.

If you had something constructive to say before it was fixed, your thoughts would have been appreciated, but your after the fact "correct me if I'm wrong" comment is just plain noise.
 
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