BMW Coolant Leak - Temp Sensor O-Ring Fix

The coolant temperature sensor has an O-Ring that can fail causing a slow or moderate leak from the sensor port located on the lower radiator hose. If you are seeing a leak under your car of coolant, and can't seem to find any major leaks double check to see that this o-ring is not leaking.

If it is, it's a very simple fix.

To replace the o-ring by itself you want part #: 13621743299

If you want to replace the whole sensor that comes with the o-ring the part number is 13621433077.

The purpose of this sensor a thermal switch that closes at high engine coolant temperatures to turn on the auxiliary cooling fan and prevent engine overheating.

The fix is shown on a BMW E46 330i, but can be used on similar BMW vehicles for the same issue.