does mmo replace your oil? for instance... if you have a 5 quart system, do you put 4 quarts of oil and 1 quart mmo?

 

I did 4.5 quarts and .5 quart of MMO. I guess you could run a full quart, kinda alot though.

 

Marvel Mystery Oil?

I wouldn't overfill. 5 quarts is 5 quarts.
I've used it in the past for a short time as a "cleaner", but never used it "full time". I was careful not to run the engine hard while it was in there, too. I prefer to run only motor oil in my motor. I don't think MMO has all of the properties of motor oil that protect the motor, but that's JMO. It does have it's uses though.

 

I always use seafoam, but you don't want to run it long cuz the filter will clog from all the crap it cleans out. I usually drive it about 15 miles then change the oil and filter.

 

my daughter used 1 quart in a 4 quart system... so 25% for 3500 miles, no problems, her mileage went from a consistant 23~25 mpg to 29~31 mpg consistantly. even after she did her next oil change.