Two-stroke oil

Two-stroke oil (also referred to as two-cycle oil, 2-cycle oil, 2T oil, or 2-stroke oil) is a type of motor oil intended for use in crankcase compression two-stroke engines, typical of small gasoline-powered engines.

Use

Unlike a four-stroke engine, the crankcase of which is closed except for its ventilation system, a two-stroke engine uses the crankcase as part of the induction tract, so oil must be mixed with gasoline to be distributed throughout the engine for lubrication. The resultant mix is referred to as premix or petroil. The oil is ultimately burned along with the fuel as a total-loss oiling system. That results in increased exhaust emissions, sometimes with excess smoke and/or a distinctive odor.

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 volumetric fuel-to-oil ratio ranging from 16:1 to as low as 100:1. To avoid high emissions and oily deposits on spark plugs, modern two-strokes, particularly small engines powering such items as garden equipment and chainsaws, may now require a synthetic oil, and can suffer from oiling problems otherwise.

Engine original equipment manufacturers (OEMs) introduced pre-injection systems (sometimes known as "auto-lube") to engines to operate from a 32:1 to 100:1 ratio. Oils must meet or exceed the following typical specifications: TC-W3® (NMMA), API-TC, JASO FC, ISO-L-EGC.

The relevant difference between regular lubricating oil and two-stroke oil is that the latter must have a much lower ash content, to minimize deposits that tend to form if ash is present in the oil when it is burned in the engine's combustion chamber. Additionally, a non-2T-specific oil can turn to gum in a matter of days if mixed with gasoline and not immediately consumed.