My previous experiments with Marvel Mystery Oil were in my 2004 Infiniti G35. This time, I decided to try it in our 2006 Honda Accord. The reason was actually not to seek fuel economy benefits, but to clean up the fuel system and injectors in particular. This car is driven short distances and as a result has a slightly rough cold idle and gets pretty bad mileage of about 17 mpg (because of short trips).
For comparison purposes, I drove this same car for 110-mile daily commute on the freeway as well as did the same with the other Accord we have in our fleet: 2007 Honda Accord. In both cases (before trying MMO), I would get 36.5 mpg at best, using all the techniques outlined in my post on maximizing fuel economy.
After I added 4 oz of the Marvel Mystery Oil (MMO) to the tank and filled it up with regular 87-octane gas, I drove it in the same fashion as always and averaged 38.5 mpg. Again, I never was able to get more than 36.5 mpg before. This is a solid 2 mpg improvement - about 5.5%. Not only that, I expect MMO to clean up the fuel system, which should be apparent at the next smog check. Stay tuned.
My web site