Been told 400 different things as far as that topic goes. Every thing from only when the change oil light reminds you, to every 3000 miles. I do it every 7000 miles or so and no ill effects from it. Of course adding that 1 quart for the mystery use at about 4000 miles. Have almost 150,000 on the clock and still running fast! Once a year should work in the case of low miles driven.