Im driving my b5 1.8t for about an hour and the engine is hot, suddenly out of no where my temprature gauge goes from middle to C(cold) while the engine is fire hot, i stop the car pull over then star then it goes half way try it again goes in the middle but then drops to C again after a minute. any suggestions ??

 

looks like your temp. sensor gone bad. I had the same problem. Just buy a sensor and install it yourself. It is ready easy to do it. You can buy it from ECS tuning.