E300 D 1996 water temperature sensor
 

Does anybody knows where the water temp sensor is located on my E300 1996 diesel?

There are several, which do you mean? Sensor for gauge, sensors for climate control, sensor for smog computer, etc.

The one that controls the glow plug relay.

Temperature switch B11, Mercedes part number 005 545 03 24, is located in the head in between cylinders 3 and 4, left (driver's) side, behind the IP and under the intake manifold. The switch operates at 60C and tells the pre-glow relay to limit the duration of afterglow, reducing it from a maximum of 180 seconds to 30 seconds. If the switch fails, the afterglow time is fixed at 30 seconds.

Jeremy