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7 Series - E38 (1995 - 2001)

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Old 08-28-2014, 06:16 AM
fearziz fearziz is offline
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Directions to replace coolant level sensor?

I know there's a bunch of threads on this but I can't locate directions to do this job, My check coolant level nightmare has begun as is the case with many others after a cold start in the morning, disappearing thereafter until the next day. I'm going to check/add coolant today and order a coolant level sensor from oembimmerparts today as well. Hopefully there are no leaks but I haven't had a chance to get under the car. Havent seen anything on the ground and there's no overheating.

quick update, car is only moderately warm now and the float is at the top of the reservoir which would indicate that the coolant levels are good, correct? Leads me to believe that the sensor is indeed bad...

Last edited by fearziz; 08-28-2014 at 06:38 AM.
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Old 08-28-2014, 02:01 PM
miguel740i miguel740i is offline
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Yes the float should poke up and out. The sensor is easy, unplug the connector at the bottom of the expansion tank. Have the new sensor ready to go, untwist the old sensor out and then pop the new one in and twist it to lock it. If you're fast you shouldn't lose too much coolant.
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Old 08-30-2014, 07:51 AM
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QSilver7 QSilver7 is online now
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Mein Auto: 1997 740iL / 2006 X5 4.4
You shouldn't have to worry about loosing all the coolant when changing the coolant sensor as long as the lid to the reservoir is on and all hoses are connected and it remains pretty much upright while changing the sensor. There are multiple chambers in the reservoir which are probably designed to serve multiple purposes...but the coolant level sensor is in a "dry well"...thus when you remove it...coolant loss is negligible or mostly nil because the sensor isn't sitting in a "chamber of coolant" inside the reservoir. The sensor detects low levels of coolant inside the reservoir based on a magnet that is designed into the bottom part of the "red float" that we see pop up when the lid is removed.

You can see the multiple chambers and "dry well" for the sensor in Jim Lev's pics below from when he dissected the coolant reservoir from an M62TU:

Q {BMW CCA Member #191509}
2006 E53 X5 4.4i (Sterling Gray) 12/05 mfg date <<~>> 97 740iL (Arctic Silver) 3/97 mfg date
99 540iT (Orient Blue) <<~>> 95 525IT (Alpine White)
91 735iL (Schwarz Black) <<~>> 85 325e (Bronzit)

Last edited by QSilver7; 08-31-2014 at 07:40 PM.
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Old 08-30-2014, 07:51 PM
sealbeach740 sealbeach740 is offline
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Mein Auto: 2000 740iS, 2003 540iS
The red coolant level rod/float (plastic) should be even with the top of the expansion tank neck when the car is level & cold (not warm).
Maybe you're checking it that way, but just to be sure......

2000 740iS. MKIV, 16x9, DDEs controlled by Euro fog light switch, reversed steptronic +/- pattern, paddle shifters, clear corners, Basslink, iPod video with stereo audio, TV tuner, gauge rings, ///M pedals, backup camera with 'on demand' switch, quad brake lights, Dinan engine & tranny software, windows/sunroof close via remote.

2003 540iS. MKIV, 16x9, PDC, CWP, TV tuner, backup camera with 'on demand' switch, paddle shifters, windows/sunroof close via remote, iPod video & audio.
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