<P> Two - stroke oil (also referred to as two - cycle oil, 2 - cycle oil, 2T oil, 2 - stroke oil or petroil) is a special type of motor oil intended for use in crankcase compression two - stroke engines . </P> <P> Unlike a four - stroke engine, whose crankcase is closed except for its ventilation system, a two - stroke engine uses the crankcase as part of the induction tract, and therefore, oil must be mixed with gasoline to be distributed throughout the engine for lubrication . The resultant mix is referred to as petroil . This oil is ultimately burned along with the fuel as a total - loss oiling system . This results in increased exhaust emissions, sometimes with excess smoke and / or a distinctive odor . </P> <P> The oil - base stock can be petroleum, castor oil, semi-synthetic or synthetic oil and is mixed (or metered by injection) with petrol / gasoline at a fuel - to - oil ratio ranging from 16: 1 to as low as 100: 1 . To avoid the high emissions and oily deposits on spark plugs, modern two - strokes, especially for small engines such as garden equipment and chainsaws, may now demand a synthetic oil and can suffer from oiling problems otherwise . </P>

Why do you have to mix oil and gas in a two stroke
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