I use Marvel Mystery also. Usually about 500 miles before I'm due for a change I'll add 1/2 a quart and run it until I change it out. I don't do this before every oil change because sometimes I forget, but have done most of the time.fearless 2000 said:I have a 2000 Trep with a 2.7 with 110,000 with no problems at all. I change my own oil every 3000 miles, before I drain the oil I pour some marval mystery oil into the engine to loosen up any crap in the engine, then I drive about 200 miles with that in the engine. I highly recomend that for everyone. I Also put techron in the gas every 3000 miles. I do not use any of that high priced oil filters or oil. all I use is the Napa oil and Napa gold oil filter In my opnion I think my car can go another 90,000 miles easilly.