Engine Temp

Hello.
I have a problem with the water temperature in my 2.5 V6 Turbo Diesel. Since I got the car, four years ago, the temp gauge pointer has always stayed dead centre once hot. Now it moves about, never reading above the centre but can read halfway between centre and cold. I have changed the temp sensor with no change. It may be the thermostat as I have noticed the temp rise to the centre mark when the engine is under load, such as 85 on the motorway, and drop when coasting down hill.
I wouldn't worry but am concerned that when the temp drop the engine management may richen the mixture too much, if the fault is electrical, and damage the cat.
I wondered if anyone has come across this problem.
Thanks for your help in advance. Mike.:1zhelp:

The cat on a tdi only gets dammaged when you put too much oil in the engine and it will get burnt on the hot cat. A tdi in good health will pass an MOT even with the cat removed. The rich mixture warning only aply to petrol engines when cranked or towed for too long as petrol will ignite when the cat gets up to operating temp. Diesel fuel wont burn with a flame inside a hot cat it will just smoke a lot ! Which CTS you changed as they are 2 on the v6 tdi, one on top of engine with a square 4 pin connector and the other on the bottom coolant hose on driver side as you facing the engine... You can read what temp is the car perceiving from the CTS with vag-com. I would get a new top CTS to be onest and see if its any change, to replace the thermostat is a cambelt off job i am afraid !

HI.
THANKS VERY MUCH FOR YOUR HELP. IT WAS THE TOP ENGINE CTS I REPLACED. SOUNDS LIKE THE BOTTOM ONE IS NEXT AS THE CAM BELT REMOVAL IS A LOT OF WORK AND I UNDERSTAND REQUIRES A SPECIAL TOOL TO SET THE CAMS.
THANK YOU AGAIN.
MIKE.
:beerchug: