MY TEMP GAUGE ON 2005 TDI 130 PASSAT IS RISING NEARER 100oC WHEN CRUISING AT HIGHER SPEEDS, IT COMES BACK DOWN TO 90 WHEN SPEED REDUCED, COOLANT LEVELS FINE AND WATER LEVELS OK, ANY IDEAS PLEASE?

100 degrees is the normal operating temperature for the motor. If it goes higher than that, the thermostate needs to be replaced. The temperature will be higher on the highway because the engine is producing more heat energy due to the higher load on the motor. Diesels idle cooler and the engine will cool down at idle or lower speeds. That is why it is best not to idle your car for long periods of time because this will cause deposits in the engine and glaze the cylinders. The engine is working normal from what you described and there is no reason to worry. I hope this helped.