For the last few weeks I have noticed my Golf 2.0 103 TDI is taking up to 20 minutes to warm to 90 degrees from an ambient 20 degrees cold start. Once warm the temperature will sit on 90 degrees in city driving but on the open road or down hill it will fluctuate between 60 to 90 degrees. The car is now over 4 1/4 years old and 65500Km otherwise faultless. I suspect a thermostat problem I am guessing stuck open. Any one come across a similar problem?