MMO is mostly a mix of petroleum solvents and light weight oil.
Ive been using it for many years to:
• 'Top-oil' gasoline engines .... 4oz.per 10 gal. of gasoline to keep the upper cylinder walls lubricated for LESS wear and retard development of 'cylinder taper'.
• To help in restoring Compression Pressure Values .... it helps loosen carbon deposits in and behind the piston ring grooves and helps to release 'sticky' piston rings. pour in a few oz. per cylinder, let sit a few days, suck out for increased compression when the rings are 'sticking'.
• Reconditioning engines that have sat for very long times and for 'releasing' engines that have 'frozen' due to internal rust. Fill oil crankcase with 100% MMO, pour in a few oz. per cylinder, and let sit, attempt to turn engine by hand to insure piston rings havent 'rust frozen' to cylinder walls and piston grooves. When 'free', spin engine with starter, let sit. Start engine with NO LOAD at low rpm until warm, let sit. Remove half of MMO and add half oil. Run with increasing load to polish the cylinder walls, etc. Remove half the mix and back to fill with reg. oil and run until next oil change to finish 'polishing'. Should be done to any engine that has been 'submerged'.
• Used to use it at 25:75 MMO/non-detergent oil for better/faster 'break-in' polishing when rebuilding, especially racing engines, etc.
With modern 'sensor controlled' engines it can foul such sensors ... there is a 'work-around' by using 'pre-chamber' mounts for the sensors but I wont discuss for obvious reasons; but, allows such altered engines to pass EPA testing when 'emission probe' / exhaust gas testing.