So Rislone is an old school engine cleaner in the same vein as Marvel Mystery Oil. It contains a very large amount of detergent and penetrating oil, to help clean up any sludge or gunk that might have accumulated in the engine over time. It's compatible with both conventional and synthetics.I had a 2009 subaru forester which was burning large amounts of oil (burning 1 quart or more / 1000 miles), analysis determined it was because of sticking piston rings. Substituting in a quart of this over the next oil change reduced the burning to a few cups (or less) over the next oil change. This also is effective for freeing up stuck lifters, in many cases.Information on Bitog indicates this is approximately a 10W-20 oil, and contains polyol esters. Overall, I would consider this an excellent oil additive for cleaning dirty engines, or engines with an unknown maintenance history.