This is the stock Bosch TDI fuel temperature sensor for all 1998-2003 New Beetle TDI and has a VW part number of 028 906 040C. Also known as the G81, this sensor has a direct effect on start of injection. A bad sensor can make your TDI injection timing unstable. Replacement of this sensor requires the Metalnerd MN3001 triangular socket which is available below for $23.00. Also required is the top quantity adjuster seal which is contained in the Bosch Injection Pump Seal Kit also listed below. A Torx T10 screwdriver or socket is required to remove the screws holding the fuel temperature sensor to the quantity adjuster.
Here is an outside link
showing fuel temp sensor replacement.