Sure as hell wouldnt make a habit of it, but I have to admit that I accidently put about 2.5 gallons of 100 octane racing fuel in my truck one day . THat was before I filled the rest of the tank with #2. I panicked, but it ran ok. Actually, it seemed to run pretty good. ONce again, not something I would do again ever. Lucas DIesel Additive for me. WOuld like to run a tank or two of bio through it just to really clean things up.