My tractor trailer holds 12 quarts of oil, is it 10 quarts of oil and one quart of MMO?  Thanks

Our normal recommendation for adding Marvel Mystery Oil to the crankcase is to replace between 10 to 25 % of the oil with Marvel Mystery Oil.  For a 12 quart system, start by replacing 2 quarts of your oil with 2 quarts of Marvel Mystery Oil.  This means use 2 quarts of Marvel Mystery Oil and 10 quarts of your regular motor oil.