Check coolant light, coolant is tad low, but "bobber is full up
 

Since moving to Charlotte, NC., starting getting the first "check coolant level" warnings since buying the car 3 years ago. Removing the cap, I find the "floater" is standing proud of the cap by a good 1.5" and appears to be all the way up, even with cool engine, but coolant is down about a pint.

Some of you have had your level indicators break, etc. There is no doubt the coolant is being lost VERY slowly, but don't understand why the bobber is riding so high still in the radiator- must be broken. Have done the valley pan gasket and cooling system once already. I can't see any coolant on garage floor, but must be leaving the car while driving. Is only way to get a new and proper working indicator to replace the expansion tank?

It's possible that the indicator is incorrect, or that the level switch is incorrect. What makes you think that it's lost coolant? The level indicator should not poke out of the tank.It should be just level. Can you poke it down and will it bob up again?

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. 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. I add coolant and after adding about a pint, the coolant is an inch from top of filler neck-technically too full. 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. I believe by how much I add that I am losing ever so little at a time, but don't know of a "broken float" issue which causes the red tipped float to stay up as high as it will go with real coolant level actually low???

Follow me? I must be losing coolant as about once a month, I get the warning and the system takes about a pint, but every time the flaot is way above the neck-cold or hot. I add coolant until I can see the coolant level and all is fine. Ignoring the float for a minute, the next time I get a check coolant light, I can't see the actual fluid level as where I filled it to last time. It's going somewhere. I fear into the combustion chamber as I am getting a short puff of smoke (white mostly) every morning when I start the car which I never used to. I guess I need to pressure test system. Float is giving me just a false sense of security and means nothing now.

Have you checked the connection of the coolant level sensor at the bottom of the expansion tank?

As far as a leak, have you ever replaced the heater hoses in the back by the CCV? These tend to develop pinhole leaks and given the location is hard to see unless you look for it carefully.

I think you may have air in your system; try bleeding it. I would share a diy, but I can't seem to find the one I've used. I'm sure you can find it using the "Search" feature.

I am perplexed by the symptoms; so all I can offer is a link that you probably already know about which shows an expansion tank autopsy.
- BMW E39 Expansion Tank Failure Analysis

We're all guessing, but, apparently, the electrical coolant level sensor and the floating stick are separate items, connected, the assumption was, magnetically.

If that's true, (that it's two separate sensors coupled together), then it's "possible" that one would read low while the other read high ... although one would think that unlikely.

BTW, my only experience with the float is here (so take what I say with a grain of NaCl):
- My radiator floating level indicator seems to be MIA (where does it go?)

http://www.bimmerfest.com/forums/att...1&d=1277234295
http://www.bimmerfest.com/forums/att...0&d=1277234143

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!

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.

Correct!

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.

Bled thoroughly when I did the valley pan gasket. Have driven the car for 6-8 months w/o a hitch. Drove 11 hours to SC and shortly after arriving I start getting Low coolant alarms. Remember, the float is ALWAYS above the neck when hot, cold, whatever. It is free as heck. Push bobber down and it pops right back up readily. I add coolant just to stop looking at the warning. I can see coolant way at the bottom, but then why does error clear for a month after I add some? Electrically, it seems to be working, but maybe top of float has seperated from bottom part. Some say when you cap, the float will get sucked down into the reservoir??? I don't see any way to take apart and inspect. Can float assembly be removed from reservoir and if so..how?

Thanks Blue.:thumbup:

I'd say it's possible because the float often separates - but - most of the time, it sinks rather than bobs.
http://www.bimmerfest.com/forums/att...1&d=1277147748

There is always an ingenious solution but, at least the obvious solution is nope. I had asked that question over here.

In fact, I have a brand new expansion tank sitting in my garage (along with the entire cooling system) just waiting for me to get a round tooit so I can start the job.

When I do, I will do an autopsy on the old expansion tank to see what it looks like. Instead of the transverse slices they did over in this autopsy, I will try a longitudinal slice to see how the float system works.

http://www.bimmerfest.com/forums/att...6&d=1277234143

If it's been 6 to 8 months since you bled the system last, I'd try that first. It's the cheapest and easiest fix.

DIY autopsy for BMW E30 radiator and expansion tank failure
 

As a cross reference, I wrote a DIY autopsy for both the radiator and the expansion tank just now.
- BMW E39 failed radiator & failed expansion tank pictorial autopsy, new questions asked

Please take a look as I posited a few novel observations that need engineering types to look at to ascertain whether or not they're valid assumptions.

http://www.bimmerfest.com/forums/att...1&d=1291020828

Bluebee.. trust this is the link.... indicator and flaot is ok, yet did not get how to check the sensor.. kindly advise

Cn90 is probably best to ask electrical sensor test questions.

He added a sensor, IIRC, to his E39.

I'd ask there:
- How to retrofit a coolant level sensor to an E39 that doesn't have it (1)

Last week I ran low without warning
 

My low coolant warning never triggered. I saw slight steam while sitting in traffic, and watched the temp gauge on on normal until the I got home and it jumped to red. (Good karma in driveway). Temp gauge told me red hot but sensor never warned me. I refilled to find the culprit as the radiator plastic-to-metal seal. Also replaced reservoir and low coolant sensor. It will be difficult to access this sensor for a change without pulling out the reservoir.
I still don't know if the new sensor is in force without running it low.

Bluebee, mr magoo and all, thank you... really i would not know what to do without you people.