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Castrol formulates engine oils that can be used in two & four cycle engines. Find out how 2 & 4 cycle engines work & what are the main differences between them.

2 vs 4 stroke engine

As a technology leader in lubricants, Castrol formulates engine oils that can be used in 4 cycle engines and 2 cycle engines. But how are 2 and 4 cycle engines different? Essentially the numbers 2 and 4 refer to the number of piston strokes the engine takes to cover the complete fuel combustion and exhaust process.

  • For a 4- cycle engine the piston moves up and then down the engine cylinder 4 times to accomplish fuel intake or induction, compression, fuel ignition (combustion) and exhaust.
  • In a 2 Cycle engine this is done in 2 piston strokes (one up and one down the piston cylinder).  The Industry and the market generally use the term 2 cycle and 2 stroke interchangeably.


How 4 stroke engines work?

A 4- cycle engine operates through 4 distinct strokes or cycles of the piston  Below are the 4 stages of a 4 cycle engine:

  • Intake or Induction Stroke- The piston moves down the cylinder. Here fuel and air are drawn into the engine for burning. Intake valve(s) open and exhaust valve(s) close to admit fuel into the cylinder.
  • Compression Stroke- With both intake and exhaust valves closed the piston moves up the cylinder and the fuel/air mixture is compressed.
  • Combustion or Power Stroke - The fuel/air mixture is ignited with precise timing forcing the piston down the cylinder and in the process generating engine power to drive the vehicle
  • Exhaust Stroke- With the intake valve(s) closed and the exhaust valve(s) open the combustion exhaust is removed
  • The 4 cycles repeat
4 stroke engine diagram

 How 2 stroke engines work?

A 2- cycle engine goes through the same process of induction, compression, power and exhaust but does so with the piston undertaking 2 strokes (up and then down).

2 stroke engine cycle

Here induction and compression occur in one piston stroke and ignition (power) and exhaust occurs in the second piston stroke. In addition, the fuel is combined with the oil and together burned during the ignition stage.


Which engine is best 2 stroke or 4 stroke?

Today 4 stroke engines are the preferred design for passenger cars and trucks. They are also used in motorcycles, lawn mowers and in recent time outboard engines.


2 stroke engines are common on small devices such a garden equipment but also are used on motorcycles and outboards. 2 strokes have the advantage of a high power to weight ratio (high power from a small engine) making them ideal for handheld equipment.


Two and Four Cycle Engine Oil 

Engine oil formulations and specifications are very different for 4 cycle and 2 cycle engines.

  • For 4 cycle engine oils the combination of select additives and base oils drive the engine performance and protection needs. Oil is contained in a sump and in turn oil pumping characteristics are key to ensure oil flow to critical engine parts. For 2 cycle engines oils the ash content of the oil is very important since the oil is burned with the fuel. It may be premixed with the fuel or injected into the engine for combustion. In some cases (2 stroke outboards) the oil is ashless. This is important to ensure proper performance and protection from deposits from exhaust port blockage. 2 stroke engines may also be diluted with a light hydrocarbon to aid in fuel mixing.


Can you use 4 cycle engine oil in a car?

A 4-stroke engine oil should never be used in a 2- stroke engine and a 2 Stroke engine oil should never be used in a 4-stroke engine. Always follow your manufacturers recommendation for proper oil specification and grade