I played around with their oil grade calculator for both the Castrol and Mobil web site. I'll have to say interesting also. On my 02 VW Jetta GLS 2.0 manual it says to use 5W-40 and 5W-30 if the 5W-30 is not available or use any oil for your climate. Ok on Castrol's web site, the grade calculator says to use 5W-40 and 5W-30 for all temps which sounds like its straight from the manual. They only have one option to choose for temps. But Mobil's web site is the one with interesting results. It gives several recommendations for the car. 10W-30 for 5-59F, 15W-40 above 5F, 5W-30 all temps, 5W-30 below 59F. They don't mention any 5W-40 and don't know why they repeat 5W-30 twice. Last time I checked the site with same search, they said 5W-30 below 59, 15W-40 above 5F, 20W-40 above 14F and another one think it was 5W-50 for all temps. There was no data for 2002 GLS model, so i used the 2001 GL. Plus the Mobil's site gives you like several engine codes but same engine while castrol has only one choice. Seems like castrol's site is more updated.