I add 3-4 ounces for every 10 galloms of fuel in my F250. When I bought the truck, the fuel gauge was very inaccurate, often taking days to rise off of empty to full. MMO did cure that with a couple of doses. The gauge rises normally after a fill up now. Everyone's experience will be different.. if it works for you, fine. I have a friend that used only 10-40 Pennzoil and 1 quart of MMO in a Chevette with the 4 cylinder diesel. It had 330,000 on it when it died. Could it have done that on oil only? Probably, but it did it with an MMO mix, and it worked for him. I won't question it. YMMV.