Temerature guage sometimes reads at the standard 90 but other times its not reading at all and sits in the off position. What could this be and will it be causing the ecu to think the car is cold and be over fuelling

Mark

mine does this every soo often i had it as temperature sender with vagcom

but since checking it doesnt come up no more

sender or thermostat not opening and closing properly prehaps.

I'd be careful about driving that if the thing is showing full temp as if it really is that hot you will damage the engine.

If you have the original (black) dual temperature sender, you could change it for the modified (green) version relatively easily which would help with the fault-finding. The part number for the modified version is 059 919 501A and the cost is £26.28. If it is the sender which is at fault, the engine ECU will be receiving incorrect information which could in turn affect how the engine runs.

My car did the same, it was this faulty sensor.

how do you change them ? is it a push fit or what

are there any washers to replace

Check this one.

http://forums.vwvortex.com/zerothread?id=1287042

Had a similar problem with the old VW Golf, started reading either nothing or max. Turned out to be a broken plastic impeller in the water pump, needed a partial engine strip to replace, but if it hadn't been found the bits could have caused terminal damage.