Can you use 5w20 for a car that calls for 5w30? I have a 2008 Lexus IS350 that calls for 5w30 and I've been using Synpower 5w30 since new. I know there have been numerous discussions on the IS forums on whether you can use 5w20 or not because there was a supposed TSB for the 2006 model (same generations as the 2008) that told the dealers to switch to 5w20. I've already read the viewpoints from the car-obsessed guys (e.g. "better mileage with 5w20" or "stick with manufacturer recommended 5w30 or you'll be sorry"). I would also like to hear the opinions from the oil-obsessed folks too.