Hi All,

 

My 09 Superb Mk2 Diesel Estate DSG has recently developed a problem where the temp gauge which used to sit rock steady at 90 degrees now fluctuates, going downhill it seems to cool down from anything from 40-70 degrees but in traffic or under load can get to more a less 90 degrees, it had a new water pump fitted 6 months ago, just wondering will the thermostat have been changed at the same time? Anyway I have changed the DSG thermostat as everyone suggests and the temp gauge problem is still the same although it does seem to drive a bit smoother, just wondered if anybody has any other suggestions as to what else it could be?

For a long time now the coolant temperate gauges have been set to show a rock steady 90c this is to reassure drivers the true temperature will not necessarily be that and could fluctuate.  It will pick up the temperature from a coolant temperature sensor and it might be that which is fault (or the gauge or whatever controls the bias).

 

If you had a scan tool plugged in recording live data you could see what temperature that picks up from the sensor - or set your dash to show oil temperature (starts at 50c on my wife's Fabia Mk3) and see if that remains steady(-ish) when going downhill.  It might not show the same figure as the coolant temperature gauge at anytime but it will I think show unbiased figures.

 

I know less about diesels than even petrol engines, so practically nothing, but I doubt the thermostat was changed unless it's a known issue but you'd soon know as you'd have been charged for the part and the fitting of it on your bill.  A drop from around 90c coolant temperature to 40c would need a steep hill into very cold weather exposure.

 

You are better to judge when your engine is fully warmed up by looking at the oil temperature than the (biased) coolant temperature gauge.

 

HTH in some way.