Many motorcycle drivers are given conflicting recommendations about what type of oil to use in their vehicles. Numerous motorcycle manufacturers heavily promote the use of specially formulated motorcycle oils, claiming that these are better for the life of the motorcycle and will not wear down as quickly. In fact, it is perfectly safe to use oil formulated for automobiles in motorcycles, as long as it is of an appropriate viscosity and the motorcycle is kept well maintained, as all motor vehicles should be.
In most cases, it is recommended that motorcycle drivers use synthetic oils in their vehicles. Synthetic is more expensive than natural oil, but will stand up to wear and tear better, and tends to keep desired properties longer. Most companies are making affordable synthetic oils available and it is well worth the minimal extra investment to be assured longer performance. Synthetic all purpose oil is still less costly than that designed specifically for motorcycles.
All oil provides a rating which indicates the viscosity. The lower the rating, the lighter the oil is, meaning that it flows very easily. This is not an issue at low temperatures, but as the engine heats up, it will rapidly begin to degrade, and get very hot. As a result, drivers want one with high viscosity to ensure smooth running of the engine at high temperatures. Many come with a combined rating such as 20W-50, indicating that at low temperatures the oil flows smoothly and as the engine heats, it retains its viscosity. Single grade is available, but multigrade is recommended.
The claim made by many manufacturers of specially formulated motorcycle oil is that which is designed for cars may actually damage the engine of a motorcycle. This is simply not true. While some designed for automotive use is not optimal in motorcycles, most oil is easily interchangeable, although motorcycles are more demanding than cars are. Motorcycles still operate along the same internal combustion principles as cars do, after all.
In scientific testing, it has been determined that motorcycles will break down oil more quickly than cars, with the results being the same for both types. Oil breaks down as repeated circulation shortens the polymers in it, causing the viscosity to be lowered. In addition, increased oxidation and repeatedly running too hot will cause it to break down and become less effective. Testing also determined that synthetic oils are not as subject to break down as natural ones, and are therefore a better choice for drivers.