Choosing The Right Viscosity
Viscosity is the most important property of a lubricant. Using too high of a viscosity oil can result in excessive oil temperature and increased drag. Using too low of a viscosity oil can lead to excessive metal-to metal contact of moving parts. Using the correct viscosity oil reduces friction and wear. However, viscosity changes with temperature. Oil gets thinner as it gets hotter, and the colder the oil gets, the thicker it is.
To select the correct viscosity for an application you need to know the operating temperature of the oil. Engines that run high operating oil temperatures require higher viscosity oil. Engines that run low oil temps require lower viscosity oil.
As you can see, the operating temperature of the oil plays a major role in the selection of the proper viscosity oil. For example, look at an NHRA Pro Stock engine, a NASCAR Cup engine and a World of Outlaws 410 Sprint engine. Each engine has a very different operating oil temperature – 100°F, 220°F and 300°F, respectively. As a result, all three engines run very different viscosity oils − SAE 0W-5, SAE 5W-20 and SAE 15W-50. The lower the oil temperature is, the lower the SAE you can run, and vice versa.
It is important to keep bearing clearances in mind. Looser clearances in the engine require higher viscosity oil to maintain oil pressure. Tighter clearances need lower viscosity oil, which provides better cooling and improved horsepower. The following page presents a chart that shows which viscosity oil is recommended for different combinations of bearing clearance and oil temperature.
Driven’s synthetic racing oils are engineered to allow the use of lower viscosity oils without compromising wear. Follow the chart below to select the appropriate oil for your application.
WHAT IS A MULTI-GRADE OIL?
Many years ago, you had winter grades for cold weather and summer grades for hot weather. A typical winter grade was 10W. A typical summer grade was 30. We often refer to these oils as straight grade oils. A 10W flows well in cold weather, so it protects the engine at start-up in cold weather. That is why it has the “W” after the 10. “W” stands for winter, but a 10W is too thin for use in the heat of the summer. So, you would change to a 30 summer grade oil that was thick enough to protect in the heat. That is why multi-grade oils were invented. A 10W-30 has both the winter cold start up flow properties of a 10W and the summer high temperature thickness of a 30 grade. A multigrade oil allows the oil to stay as close to the optimum viscosity over a range of temperatures − not too thick when it is cold and not too thin when it is hot. Today, advanced synthetic, multi-grade oils like Driven’s 0W-20 provide engine protection in temperatures as low as -40°F and as hot as 340°F.
VISCOSITY CHANGE WITH TEMPERATURE
Since all oils get thinner as they get hotter (and get thicker as they get colder), the charts below show the viscosity change from 100˚ F to 300˚ F. You can use these charts to select the best viscosity for the operating temperature of your application (not too thick nor too thin).
RELATIVE VISCOSITIES
The first two charts below display the relative viscosities of the Driven line of synthetic race and driveline oils. Most people assume that a 70W-80 gear oil is thicker than 15W-50 motor oil, but that is NOT the case. SAE viscosity grades for gear oils are not thicker than SAE viscosity grades for motor oils. The charts explain how the Kinematic Viscosity (measured in Centistokes) of each product compares to the others at 212° F.
