Two-stroke oil (also referred to as two-stroke oil, 2-stroke oil, 2-stroke oil or 2-stroke oil) is a special type of motor oil intended for use in two-stroke engines with crankcase compression.

A two-stroke engine uses the crankcase as part of the induction tract, unlike a four-stroke engine whose crankcase is closed except for its ventilation system, and thus, oil must be combined with gasoline to be circulated in the lubrication engine. The resulting mix is referred to as premix or petroleum. As a total-loss oiling method, this oil is finally burned along with the gasoline. This leads, often with excess smoke and/or a distinctive odor, to increased exhaust emissions.

Petroleum, castor oil, semi-synthetic or synthetic oil may be the oil base stock and is blended (or weighed by injection) with petrol/gasoline at a volumetric fuel-to-oil ratio of 16:1 to as low as 100:1. Modern two-stroke engines, particularly for small engines such as garden equipment and chainsaws, may now need synthetic oil to avoid high pollution and oily deposits on spark plugs and may otherwise suffer from oil problems.

Pre-injection systems (sometimes referred to as ‘auto-lube’) for engines to operate from a 32:1 to 100:1 ratio have been developed by engine original equipment manufacturers (OEMs). The following typical requirements must be met or exceeded by oil: TC-W3TM, NMMA, [API] TC, JASO FC, ISO-L-EGC.

The relevant difference is that two-stroke oil must have a much lower ash content compared to periodic lubricating oil with two-stroke oil. This is important to minimize deposits which tend to form if ash is present in the oil that is burned in the combustion chamber of the engine. In addition, if blended with gasoline and not consumed immediately, a non-2T-specific oil will turn into gum in a matter of days. Another major aspect is that 4-stroke engines have a different ‘stickiness’ criterion than 2-stroke engines do. Various types of two-stroke oil have been developed for specialized uses since the 1980s, such as two-stroke outboard motor, two-stroke premix oil, as well as the more standard two-stroke auto lube (motorcycle) oil. As a rule of thumb, most commercially offered containers of oil would have printed somewhere on the label that it is compatible with ‘Autolube’ or injector pumps. These bottles seem, if shaken, to have the consistency of liquid dish soap. A more viscous oil can not be passed through an injection system efficiently, although either type can be run on a premix machine.

‘Racing’ oil or castor-based oil offers excellent lubricity – at the cost of premature coking. It will not garner a substantial improvement in efficiency for the typical moped/scooter/trail rider and will entail very regular teardowns.