Siaman

Read my post again. I'm not promoting the thin oils on the old cars. Clearly they are available today and some people ignor the manual. Again, my 90 300-E likes 20-50 summer - 15-40 winter. I once tried a 5-30, it knocked more and I took it out the same day. As far as tolerance on new cars. you can void a GM warrenty on their engines for years now if you go over a 10-30, so it's an indication they have more concerns than just milage. Personally I like a "not so tight" engine that takes a thicker bodied oil. I think they pass small micron dirt easier and last longer.