So your low coolant (antifreeze) light came on and your coolant level is low. You have a leak, but where? BMWs have multiple components in their cooling systems and any of them could cause a leak, however the most common of coolant leaks are caused by a failed Coolant Temp Sensor located (in most cases) in the lower radiator hose
Checking the sensor for a leak is simple, just open your hood and look down at your lower radiator hose, find the sensor and you can see coolant remnants originating from the sides of the sensor and you should see a pool of coolant under the hose onto your lower engine panel.
Replacing the sensor can easily be accomplished by the average DIY guy, or gal. First step, make sure the cooling system is NOT hot! Open the reservoir aka (expansion tank) cap to relieve the pressure. Screw cap back on. (Putting cap back on is important if you don't want a mess) unplug connector, squeeze tabs and lift sensor out of radiator hose. Some coolant will come out but not much. Install new sensor (it comes with new O-Ring) and plug electrical connector into new sensor. Now you need to correct the coolant level (make sure not to overfill the system) Perform a cooling system pressure test to ensure no other leaks are present. Put on cap and clean off the spilled coolant with water. Your done!
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Electrical connector unplugged
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Removing faulty sensor from lower radiator hose
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Correcting coolant level with Factory OE BMW coolant
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Fluid level is correct when float reaches top (don't overfill for it can cause more leaks to occur)
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Pressure test to make sure no more leaks are present
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Coolant Temp Sensor Part number 13621433077
This is the coolant temp sensor that you will need to replace. Part Number is
13-62-1-433-077 and will cost about $30.00 from the dealership parts dept.
The same part is applicale for many modles including: E38 E39 E46 E52 E53 E60 E61 E63 E64 E64 E65 E66 E70 E70 E71 E72 E82 E83 E85 E86 E88 E90 E91 E92 E93 F01 F02 F04 F06 F07 F10 F12 F13 F30


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