I have noticed alot of you guys have been adding one quart of 15w-50 to your oil changes. Example: i once read someone put 4 of 5 quarts of 5w-30 mobil 1, and finished with 15w-50 as there 5th quart. Why are some fo you doing this?? I dont know much about any of this besides my synthetic does a really good job of protecting my engine. Can someone let me in on why some of you are doing this? I am running all 5w-30 m1 in my 03 cavalier, is there an advantage to adding 15w-50?