Ed has tuned them and must not have had any negative feedback with problems from the heavier weight oil but there's no way he would pay for repairs if it did cause a problem. I would run the 5w40 in the summer and 5w30 in the winter.I'm tuned already, VW won't pay for shit anyway. This is why I am even looking into it. If warranty is likely voided, might as well say fuck it and protect myself by going 5w40. But I am still investigating.