I see real results in mpgs with Marvel Oil.Again full bottle to diesel and gas tank every other fillup.
My diesel went from 32 mpg to 36 mpg.
My S went from 20 mpg to 23 mpg,city driving.
I tried other lubes like 2 stroke oil with diesel,but MMO is the best.
Now to much MMO in a gas engine will foul your plugs,and get you worse mileage.But 8 oz. to 26 gals. gasoline seems to be the magic number.
Now seafoam run thru a vacumm line in a gas engine,you can see black stuff in exhaust from valves.When its treated, then it fades after cleaning valves.I perfer Techron to clean injectors when on sale,or I use a generic.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt