Bimmerfest - BMW Forums - View Single Post - Check coolant light, coolant is tad low, but "bobber is full up
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Old 11-15-2010, 01:19 PM
mtnbimmer mtnbimmer is offline
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Location: Colorado
Join Date: Mar 2010
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Mein Auto: 325ix, 540iT
Originally Posted by 540iman View Post
What makes me think I have lost coolant? The low coolant warning on the dash and the fact that I can't easily see the coolant level by looking in the reservoir.
Normally you can't see the coolant when you look down the filler neck. That what the level indicator is for. The low coolant warning on the dash is based on an electrical signal. If the level indicator is showing full (or in your case overfull...), I would start checking the coolant level sensor!

Originally Posted by 540iman View Post
The float is full up sticking 2" above the neck. I push it down and it is free and "bobs" right back to way above the neck.
Your way overfilled on coolant!! Per the manual, the top of the float should be no more than flush with the top of the filler neck.

Originally Posted by 540iman View Post
I add coolant and after adding about a pint, the coolant is an inch from top of filler neck-technically too full.

Originally Posted by 540iman View Post
If the float is so high, I don't know why I'm getting an alarm in the first place unless the float below the bobber is down telling the system I'm low.
Again, check the level sensor. If the level indicator (bobber) is "floating", I would almost guarantee that you have coolant in the expansion tank.

I'm guessing that when you overfill the cooling system, when the system gets up to correct temperature the system "burps" the excess coolant out and in the process dumps a little to much coolant. When the system cools down, you end up with a low level. I had this happen to me a few times on my e28 hydraulic system. I know they are two different types of systems, but the principle is the same. I'm not sure you even have a low level, based on what you see with the level indicator. I would trust the level indicator ("physical" indication) more that I would the level sensor (electrical signal).

As mentioned above, the other thing to confirm is that your cooling system is bled correctly. Trapped air can create all kinds of false indications/readings.
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