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Old 02-25-2008, 08:12 AM   #1 (permalink)
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Question Coolant level sensor

Hi, I just changed the thermostat and while driving the coolant level light came on yesterday. Checked, correct, the coolant dropped a little during the repair, but I then topped the coolant and the light is still on ??

how does the coolant level sensor work? I searched the forums but only found some answers on bmw forums which may not apply to mercs I think.
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Old 02-25-2008, 08:45 AM   #2 (permalink)
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Check the water level in you windshield washer tank as well. For some reason "they" decided that both tanks should go through the same warning system...
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Old 02-25-2008, 09:57 AM   #3 (permalink)
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I filled that up too, no change.. since it fired because of low coolant and stayed on after it seems unlikely to me that the sensor failed.. but I cant be sure..
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Old 02-25-2008, 10:23 AM   #4 (permalink)
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OK, the radiator tank is full, the washer tank is full, and the float in the fill neck is free to move, right?
The next likely thing is the sensor itself.
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Old 02-25-2008, 10:57 AM   #5 (permalink)
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the float, I am not sure about that, I noticed a plus sign while filling but I don't see it always.. how does the float and the sensor work together?
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Old 02-25-2008, 11:29 AM   #6 (permalink)
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Lightbulb

ok, I searched the posts about the float, I will try to pull it up with a screwdriver to see if it moves freely inside.
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Old 02-25-2008, 06:09 PM   #7 (permalink)
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Quote:
Originally Posted by Bruce R. View Post
Check the water level in you windshield washer tank as well. For some reason "they" decided that both tanks should go through the same warning system...
Not the case on my '99. There are separate indicators for each. It is true that the two sensors are wired in series, but they also each have separate series/parallel resistors in them, so that the instrument cluster electronics can tell which sensor is triggered. In the diagram, S41 turns on E11 (coolant) and S42 turns on E13 (washer).
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Coolant level sensor-sensors.jpg   Coolant level sensor-coollantsensor.jpg  
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Old 02-26-2008, 01:46 AM   #8 (permalink)
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Smile

Thanks to both of you, I pulled the float a little bit and now the light is off. It is just under the surface of the fluid and I assume it is ok.
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Old 02-26-2008, 06:16 AM   #9 (permalink)
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Quote:
Originally Posted by DickB View Post
Not the case on my '99. There are separate indicators for each. It is true that the two sensors are wired in series, but they also each have separate series/parallel resistors in them, so that the instrument cluster electronics can tell which sensor is triggered. In the diagram, S41 turns on E11 (coolant) and S42 turns on E13 (washer).
OK, I'm sure you are correct, the '32 may be slightly different, and things have obviously changed.
My radiator fill light came on for no apparent reason with the tank "full" and the washer tank low. I added fluid to the washer tank as has been described in some other posts that I recalled and the light has not come on again.... The washer needed almost a gallon of fluid to bring it up to full... !

Thanks for the schematic, it helps a lot.
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Old 02-26-2008, 10:52 AM   #10 (permalink)
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On my 99 SLK230, I had the same problem. After the dealer replaced the coolant level sensor two or three times under warranty, they filled the windshield washer tank and the problem disappeared. So, maybe some cars are different or maybe things changed since my car was built but that was my experience.
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