Hi, Sometimes I get the impression that it is believed that when a car gets older, the thing to do is increase oil viscosity. If you arent consuming oil, why do it? My girlfriend's car specs 5w-30 and we use that (just changed to mobil1, Im not worried about it being light because its an acura, which now uses 5w-20) My fathers van uses 10w-30 as suggested from the very beginning, its totally fine at 150k on 7500mi dino changes. My diesel Mercedes should use 15w-40 according to the book, but I have changed to delvac1 5w-40 about 10k ago and are now over 200K... No oddness, or oil consumption. Is there any reason why I would ever want to consider upping the viscosity? The cars seem to be doing well on their own.