l have a 1995 306d (non turbo) which has been off the road for a number of months but now wanna run it over the winter. During preparation l have noticed that when the engine is cold and l turn the ignition on the temperature gauge goes straight to the hottest extreme on the dial. Please help...

The temperature is measured by a sensor that is screwed directly into the radiator. It is a fat sensor, about 1 inch in diameter. Look for it a few inches below the filling neck/fill cap of the radiator. Inside that sensor is a metal coil that is affected by the heat. The hotter the water, the more electricity passes through the sensor.
l feel this sensor is faulty.
The test for my theory is to disconnect the wires attached to the sensor, & see ur temperature gauge fall to the left, the extreme cold side.

Notice that there is probably a thin metal clip that must first be removed, before the plastic connector can be pulled off .
The metal clip is a wire about the thickness of a paperclip, & it is a rectangular ''U'' shape.

If u would like a photo of this piece, just ask me & l will post a link to a photo for you.