I had a Ford 7.3L for a couple of years and never ran an additive. I probably didn't own it long enough though. I replaced with a 5.9L Cummins mainly to go from 2wd to 4wd. I couldn't find a good 4wd 7.3L at the time and we were far enough into the 6.0L's to know to avoid them. I've had the Cummins for a little over 9 years now. Never added anything and never had a problem.