I recently purchased an 08 Jeep Grand Cherokee and the manual calls for 5/20wt oil. I then read an article from a lubrication firm stating that these low weights were recommended because the manufacturers needed them to meet CAFE mileage standards. It also said this was done to the detriment of the engines which would do better on 5/30w. I believe I am out of warranty at 60K and was considering switching to the higher weight at the next oil change and would appreciate any thoughts on this oil weight situation.