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E85 / E86 Z4 (2003-2008)
E85 Z4 Roadster, E86 Z4 Coupe, E85 Z4 M Roadster, and E86 Z4 M Coupe talk with our BMW gurus here.

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  #1  
Old 03-19-2014, 09:57 PM
igeak691 igeak691 is offline
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Location: New York
 
Join Date: Feb 2014
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Mein Auto: 2003 Z4
Taking out coolant expansion tank sensor

Is it true that you can remove the sensor on the bottom of the expansion tank without all of the coolant coming out? I was told that the coolant sensor sits in its own separate compartment but I don't get how this will measure the coolant level if it does. Common sense says if I remove the sensor from the bottom of the tank, all of the coolant will come out.

Reason I'm asking is because the coolant light is on when I start the z4 but it turns off after about 20 minutes of driving. Intermittently it will turn on and off after that, but I checked the coolant level and it is full. It does go down a little bit after a few days to a week, so I'm wondering if maybe some coolant is leaking through the sensor and causing this type of on and off coolant light behavior.
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  #2  
Old 03-19-2014, 10:49 PM
igeak691 igeak691 is offline
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Did a little more research. Coolant level sensor is not bathed in coolant. Float inside tank has a magnet attached to it, so that when coolant is low, sensor will close the circuit and turn on the light on the dash. Still doesn't explain it for me, but I'll try using my old (working) sensor instead of the new one that came with the tank. I'll also try playing with the float to see if I can get the dash light to turn on and off, simulating low or full levels of coolant.

Any words of advice appreciated.. going to clean up the coolant residue and see if any more pops up to rule out residual leaking coolant after replacement of expansion tank.
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Old 03-20-2014, 07:27 AM
coolvt coolvt is offline
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You said the coolant level goes down after a few days to a week. Question is, where is that coolant going? Exactly how much is being lost?
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Old 03-20-2014, 08:39 AM
igeak691 igeak691 is offline
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Both times I accidentally opened the cap when it wasn't fully cooled so I'm not sure if its residue from that or something else. Will have to clean everything up and remember to only open the cap after letting the car sit overnight
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Old 03-20-2014, 07:02 PM
igeak691 igeak691 is offline
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Nope. No issues with coolant leaking. Siphoned some out today to get it to be between max and min.. before it was way above max, about a cups worth.

Also checked the sensor and it is working. When a magnet is near it, it closes the circuit. Car checks level sensor when switching on, but bridging and unbridging won't make the light go on and off instantaneously. I'm guessing the car computer checks every so often. Now I have to figure out why the light is on (meaning the magnet isn't hovering over the sensor), and then after driving 20 minutes, light goes off, meaning that the magnet/float is now in the right place. Any ideas?
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Old 03-20-2014, 07:13 PM
igeak691 igeak691 is offline
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Seems to be that this thread (http://www.bimmerfest.com/forums/sho...d.php?t=501999) shows that the sensor works opposite of how our Z4's work. Today, when I bridged the contact, the light DIDN'T go on. When I didn't bridge it and left the plug unplugged, the light DID turn on. Since the sensor closes the circuit when a magnet is near it, this would cause the opposite of what should happen. When the tank is full, the float will be up, and not envelope the sensor, thus keeping the circuit open and turning on the light (when it shouldn't be on) and when empty, the float will be at the bottom, enveloping the sensor and closing the circuit and turning OFF the light.. so confused.
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