I learned from this forum and around the net that this is a pretty common problem for our superb. Previously it was smack in the middle at 90c but recently it picked up a habit of suddenly dropping to 1 bar above 0 and after a few moments goes back up again.and the cycle continues until i turn off the engine.

Most probably the either temp coolant sensor or thermostat. I will proceed with the sensor 1st and see if it cures it.but i wanna make sure i got the correct part.is there any reference i can forward to the part shop?

Did a little more search came across the G62 sensor.is it the exact same part on 1.8t as on 1.9tdi?

Get a new sensor.  I have had it replaced TWICE this year.  First one was a $4 sensor from ebay with a TWO year guarantee.  Failed after a month.  Didn't bother with refund exchange etc.. bought another one for $7, made by Hans Pries... it's perfect.

You will have some coolant loss when replacing, so make sure you have a litre of the pink coolant and/or distilled water.  I just topped up with water as my antifreeze was quite fresh and high concentration.

I got it replaced.abt £15 with o ring.used replacement from meyle germany.now all is good