Sorry to bring up an old thread but I hate seeing information that is wrong or incorrect as others may be confused by it and it defeats the object of the forums to help people with correct information.
I am afraid Critter7r's 13 years in parts and service at 2 BMW dealers did not serve him well on this one. There is no such thing as a heating element in the coolant level sensor. There is no pocket of air for heating or cooling and no readings are taken, it is a simple magnetic float switch that operates around the outside of the tube in which the sensor sits. This is fitted to ALL the E46 models.
Hope this helps, Dan
Thanks for the update.. I also found this out when I replaced my expansion tank in the summer of '08. What the hell is that thing rattling around inside the tank? Oh, it's a little something wrapped around the tube that the coolant sensor gets stuck into. So it would appear that the coolant sensor works very similarly to how the old E30 and E36 coolant sensors work, except that you can remove them without losing any coolant.
I didn't think to go back and try to find this thread to update, but cool that you did!
Yeah, at first i was like "hey I thought that thing was a magnet."
Then I thought, "man that sapote guy is a jerk".
Then I accepted that you learn something new everyday, even on an old thread.
If you look at the sensor though, it sure looks intricate for just sensing magnetism. I can see how it could apear to be a heated sensor.
My theory on why the light doesn't always come on: Engine Sales!
The coolant temp sensor is a magnetic switch. if you remove the sensor no coolant comes out right it's a dry sensor. there is a float inside the jug with a magnet in it. when the coolant level is low enough the float sits down over the glass bulb of the sensor and the magnet of the float causes two contacts to touch each other inside the sensor and cause a complete circuit. The instrument cluster sees this complete circuit and then knows the coolant level is low.
You gotta be shitting me, right?
Finished reading the rest of the thread. Good discussion and info.
Sapote, the guys really showed you some grace on this one. Critter was attemtping to explain it as best he could.....
Be glad you got help. Also as an aside, when you start a thread, asking for help/information, and it is provided, an acceptable response is "Thank you" and is much appreciated.
So I will say it for you. Thanks go out to Nathan, Critter, GP, and the others who contributed and took valuable time away from their day to try and help Mr Sapote.
Last edited by danewilson77; 12-02-2009 at 09:19 AM.
Even though our two-year-old discussion of the operation of the coolant level sensor was .. well, quite wrong?
At least it's resolved now. The magnetic-switch explanation makes somewhat more sense than the heated-wire explanation. I still don't think it's a reliable indicator of catastrophic cooling loss (i.e. ruptured expansion tank).
To provide enough warning time for coolant loss, the sensor needs to be located part way up the tank rather than at the bottom of the tank. By the time the sensor contact gets made at the bottom of the tank, all coolant has drained out.
Also for those interested, the proper term for magnetically activated switch/sensor is call a Reed switch/sensor.
Yeah, same principle works with the screen washer tank. I couldn't believe the cluelessness exhibited in earlier posts.
My coolant light came on suddenly yesterday while driving under ideal conditions. Today, I checked the level and it's at max. So my guess is either the float in the tank got stuck at the time of the light, or my level sensor is kaput. I need more observation time to see which is which.
Dan, you are the man!
1) I just removed my ET and cut it open to extract the dipstick/float which has a simple magnet on it. Then I looked at the coolant level sensor under magnification to see that it is a simple magnetic switch. I put an ohm meter on the sensor leads and it read open circuit, then I held the magnet from the float next to the sensor and it read closed (0 ohms). This is a super simple mechanism that just closes the sensor switch when the float's magnet is near it, at low coolant level when the float is at the bottom.
2) My testing indicates this level is sampled when you start the car. If I jumpered the sensor's plug on the car and started it, the dash light would be off. Pull the jumper out and it stayed off. Shut down engine and restart and the dash light was on. Apply the jumper and it stayed on.
EDIT: And I just now realized that my jumper tests in #2 contradict how the sensor works as measured in #1. Crap! And after reading other posts in other BMW forums I see the same confusing observations that I made. What the heck is going on with what should be a bone-headedly simple thing?
Someone REALLY needs to delete Critter7r's posts from this thread, they are so wrong, and this forum thrives on correct advice.
Last edited by balidawg; 07-28-2013 at 01:34 AM. Reason: clarify contradiction
Need a DME or EGS update?
https://forum.e46fanatics.com/showthread.php?t=1081716
Coding 530i after AT->MT Swap
https://www.bimmerforums.com/forum/s...ter-AT-MT-Swap
Level detection works at all times. Here's the real reason for intermittent lights:
http://forums.bimmerforums.com/forum...-light-fix-E46
Okay, but can you kindly explain how this works? If you're implying that incorrect coolant bleeding leaves air in the float cavity and causes the float and its magnet to sit at the bottom of the ET, then yeah ithat makes sense.
But here is the thing, my float is at the top. I know this because I can see the little white sucker in there and it is pushing the red stick to the top. So the float is definitely not near the sensor yet the dash light is on. Please explain how this could be.
Also, I can push the red stick all the way down with a skinny screwdriver until the float is at the bottom and the dash light is still on. I let go of the red stick and the float goes quickly to its topmost position and the dash light is still on.
Something is really misunderstood here. Anyone who truly understands how the sensor and dash light work, please explain.
Need a DME or EGS update?
https://forum.e46fanatics.com/showthread.php?t=1081716
Coding 530i after AT->MT Swap
https://www.bimmerforums.com/forum/s...ter-AT-MT-Swap
Ah, you're not the first one to give incorrect advice. Done it myself a few times...no worries.
I tested the sensor carefully and it functions as expected. It is normally open until a magnet comes near it, then it is closed. This is how the Bentley manual says it should operate and also makes sense, because the magnet on the float passing over it is what closes the circuit to turn on the dash light.
I checked the leads in the plug that go to the sensor and they measure 12V.
Need a DME or EGS update?
https://forum.e46fanatics.com/showthread.php?t=1081716
Coding 530i after AT->MT Swap
https://www.bimmerforums.com/forum/s...ter-AT-MT-Swap
Have you tried swapping the sensor with the one in the bottom of the washer reservoir? They're the same part number.
I have not. But I did remove the sensor and perform tests on it and it's working fine. I will pull out the washer level sensor and check it as well. Thanks.
The thing that is confusing to me is the wiring/dash light side of it. The dash light is on when the sensor plug is not connected and off when I short the sensor plug leads. This seems opposite to what it should be based on how the sensor works.
If anyone here has been down this road (I have searched all the forums, googled, etc., for hours) and understands why my dash light circuit seems to behave opposite of how it's supposed to, by all means jump in and straighten me out.
Need a DME or EGS update?
https://forum.e46fanatics.com/showthread.php?t=1081716
Coding 530i after AT->MT Swap
https://www.bimmerforums.com/forum/s...ter-AT-MT-Swap
Just swap them and see if the sensor is good or bad.
Okay, I just thought of something. Maybe the way this mechanism works is that the float magnet has to be at just the right vertical position to keep the switch closed and the dash light off? Any other float position, too high or too low, and the dash light comes on? If this is is true, then it implies that the coolant level must be kept precisely correct, otherwise it's dash light city. Hmmm...this theory is starting to make sense given how critical the ET's coolant level is.
Anyone care to comment on this theory? This mystery is killing me...
Need a DME or EGS update?
https://forum.e46fanatics.com/showthread.php?t=1081716
Coding 530i after AT->MT Swap
https://www.bimmerforums.com/forum/s...ter-AT-MT-Swap
Need a DME or EGS update?
https://forum.e46fanatics.com/showthread.php?t=1081716
Coding 530i after AT->MT Swap
https://www.bimmerforums.com/forum/s...ter-AT-MT-Swap
Actually, it's the air pocket in the tank that gets compressed when the coolant heats up because the coolant expands, which causes the coolant jug to be more full when HOT, and less full when COLD. That's also why many people that are only very slightly low on coolant come in and complain that their coolant light is on in the morning, but after they drive a few miles, it goes off.
The switch is normally open which means that the magnet is suppose to close the switch when coolent is at the right level. It is designed this way so that in the event of a failure in the external cable, switch or magnet you will get a check coolent message to troubleshoot. By jumpering the wire harness sockets you are similating a closed switch with sat coolent level. This verifies your harness and computer are working properly.
I'm currently trying to determine if my switch is bad or if the tank is the problem. I have a check coolent level indication that will not clear. Whats making this difficult for me is that I need to unmount and lift my tank to get to remove the switch. The mounthing bracket under the tank prevents me from getting access to it with the tank installed.
The way a reed switch works is that it has an actuation point and release point. The magnet needs to be pass the upper portion of the switch for it to close the contacts and it will keep it closed untill it hits the release point. Therefore there is a range on the switch where it will close and stay closed and open and stay open. With the switch engaged the coolent level may need to drop ~ 1 1/2" (best guess) to cause the switch to open. To clear the alarm you would need to fill the tank to the correct level in order to get the switch to close again. One reason people get intermittent alarms is due to them trying to top off the tank when the coolent/engin have not completely cooled therefore not filling the tank to the correct level. Air pockets in the tank which can be created when inproper bleeding is perform can also force the magnetic below the the swich actuation point giving you a false impression that the liquid level is low when infact its correct. I'm guessing thats why they place a bleed valve directly above the level switch.
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