Most of a motorcycle engine’s wear happens at start up. Welcome to the wonderful world of oil viscosity.
Viscosity is the term used to describe a fluid’s resistance to flow. Generally, the colder a fluid is, the thicker it becomes and the slower it moves. Conversely, the warmer a fluid becomes, the thinner it becomes and the faster it moves.
Engine oil viscosity is categorized by two numbers that are separated by the letter W, which stands for winter.
The first number, rated at 0° F, details an oil’s viscosity at low temperatures. So, for example, 10W-30 oil has less viscosity than 20W-50 oil and will therefore flow more freely during an engine cold start.
The second number details an oil’s viscosity at the other end of a temperature range, at 212° F. Again, if we take the previous example, you can see that 10W-30 oil has less viscosity at high temperatures as 20W-50.
This is where the term multi-grade comes in. By blending different grades of oil—grades with different viscosities—engines can be optimally protected at both low and high-temperature riding. Oil can be blended in such a way that it retains the correct thickness and flow rates to offer protection based on the particular requirements of one engine over another.
Starting your bike from cold, outside on a chilly Fall morning means that lots of delicate metal parts will start bouncing around at speed with only engine oil to protect them. Cold, thick and slow moving oil is going to take a little longer to coat and protect those delicate engine components. Worse still, cold, thick oil may not even be able to penetrate areas of an engine where gaps can be as small as .002.
This is why generally speaking, high revving machines such as motorcycles are required to run on a 10W or 20W, which ensures that moving parts get coated quickly, even in the cold and despite rapid engine revolutions at start up.
Your owner’s manual will tell you what viscosity rating the oil in your machine should be.