07-29-2014, 10:32 AM
The viscosity of a multi-grade oil like 10W30 or 20W50 changes with temperature. Viscosity is simply the ability of an oil to flow. The first number/letter, eg. 10W is the viscosity in winter temperatures and the second number is the viscosity at high temperatures.
Misconceptions:
1) oil viscosity has nothing to do with its ability to carry away heat or cool an engine.
2) Oil viscosity has little to do with its ability to reduce friction.
3) Harleys and some other bikes generate very high cylinder head temperatures, especially near the exhaust valve. Using a 20W50 weight oil supposedly allows the engine to better tolerate those high temperatures. However, that may be simply due to old fashioned thinking. Indy racers typically run very low (0W) viscosity oil to get faster flow thru the engine and coolers and require less power to pump the oil.
4) Synthetic oil is not necessarily "slicker" than petroleum oil. That capability is largely a factor of the friction modifier additives in the oil. The main benefits of synthetic is the ability to tolerate extreme temperatures and the ability to not break down over time.
Misconceptions:
1) oil viscosity has nothing to do with its ability to carry away heat or cool an engine.
2) Oil viscosity has little to do with its ability to reduce friction.
3) Harleys and some other bikes generate very high cylinder head temperatures, especially near the exhaust valve. Using a 20W50 weight oil supposedly allows the engine to better tolerate those high temperatures. However, that may be simply due to old fashioned thinking. Indy racers typically run very low (0W) viscosity oil to get faster flow thru the engine and coolers and require less power to pump the oil.
4) Synthetic oil is not necessarily "slicker" than petroleum oil. That capability is largely a factor of the friction modifier additives in the oil. The main benefits of synthetic is the ability to tolerate extreme temperatures and the ability to not break down over time.