You might get away with it, but I wouldn't try it. I've heard about this phenomenon more than a few times. That dark stuff is not good to run.Hmmm hadn't thought of that. There was only a couple gallons in the tank I think, it was at about 1/8 tank on the gauge. I put in near 6 gallons which brought it up closer to half a tank. So far so good driving for maybe 5-10 minuites around the neighborhood. I was thinking once it's registered to run it around town enough to run out what's in it then put in another maybe 5 or so gallons and repeat and continue to dilute and flush it out.