Easy your half right, the older 12 valve cummins takes 2.5 (10 quarts). 16-18 sounds doable but I have a hard time believing 20+ mpg in any full size pickup. Doing all the mods on diesels are way more expensive, I can buy lots of gas and spark plugs for that. Not trying to sound like a hater, Corry and easy, but for me it don't make sense.