Yeah I know many people recommend to use full synthetic for the VW. I got a 02 VW Jetta GLS 2.0 so its not a high performance engine and I don't think synthetic is required for this engine. I would like to do 3000-5000 intervals using conventional oil. So which do would you recommend me to use? 5W-30, 10W-30, 10W-40, 15W-40, 20W-50? By the way the car doesn't consume too much oil. I was thinking about using 15W-40, but not sure if it will really drop my gas mileage or affect catalyst activity. Thanks for any replies.