It is mainly for improved gas mileage (less drag on the crank and oil pump). When I bought my wife's 2004 Grand Marquis the 0W-20W was recommended but when used it was so thin the lifters would rattle when first started. I used it though till it was out of warranty then went to a thicker grade synthetic. I target for changing the oil @ 3000 miles but always miss it. I try not to go over 5000 miles regardless.