Jaguar XJS V12 1989. The temp gauge on the instrument panel indicates the engine is running cool. The needle is half way between cold and normal. This just happened about two weeks ago. Previously the needle was dead center on normal. The engine runs just fine. Does this mean the sensor is bad and should be replaced? If so, what is the part number I need to get? Any help is greatly appreciated

 

Try cleaning the connector on the transmitter. If there is a bad connection or ground the gauge will read low.

 

Also try running an extra ground from the flexible circuit board.

 

Is there a diff in outside temp? My gauge does this on the threshold of the T-stat opening. It'll go up and there will be an obvious drop when the T-stat opens up. Most of the time sits about half-way between Cold and N

 

Likewise with mine, 1/2 way is the Norm.

Maybe an air bubble finally found its way out.

The other suggestions are very sound, and should be done as a priority.