I am no expert (see thread on warranty issues for disclaimer) but I suspect that some heavy contaminates may stay in the oil pan and never even make it back to the oil filter. I don't have a horse in this race, so I have no objection to anyone trying anything they want to with their own truck. To me, it's not worth the risk of damage to save a few bucks, plus I only change my oil twice a year (6 gallons total), so there's not much money for me to save anyway.