Choosing The Right Viscosity


Viscosity measures the resistance to flow. Higher viscosity grades have more resistance to flow than lower viscosity grades. Oil gets thinner as it gets hotter. To determine the correct viscosity for an application you need to know the operating temperature of the oil in that application. Engines that run high operating oil temperatures require higher viscosity oil. Engines that run low oil temps require lower viscosity oil.


Years ago, it was common practice to use lighter “Winter” grade oils during the colder winter months, and then switch to a heavier oil for Summer driving. Accordingly, the number before the “W” reflects the “Winter” cold start flow of the oil. A lower number before the “W” indicates better cold start protection (lower viscosity base oil). The number after the “W” indicates the flow rate at 212°F (high temperature viscosity). Since most race cars don’t run in sub-zero conditions and oil temperatures vary above and below 212°F, the “Operating” viscosity of the oil is what is important – not the SAE grade.

So now that you know about viscosity grades and viscosity index how do you use this knowledge?

Even with a high viscosity index oil, viscosity still changes with temperature, so selecting the correct viscosity for an application requires knowing the operating temperature of the oil. Engines that run high operating oil temperatures require a higher viscosity grade oil. Engines that run low oil temperatures require lower viscosity grade.

For example, an NHRA Pro Stock engine runs at very low oil temperatures – only 100F. A NASCAR Sprint Cup engine runs 220F oil temps and a World of Outlaws 410 Sprint engine sees oil temps as high as 300F. Each engine has a very different operating oil temperature – 100°F, 220°F and 300°F. As a result, all three engines run very different viscosity oils − 0W-5 for the NHRA Pro Stock, 10W-30 for the NASCAR Sprint Cup and 15W-50 for the World of Outlaws. The best thing to remember is the lower the oil temperature, the lower the viscosity grade you can run, so having a good oil cooler can really make a difference.

Choosing a motor oil with a higher base oil viscosity index provides the benefit of improved flow when it is cold while maintaining oil film thickness at high temperatures. Conventional mineral base oils have a viscosity index in the range of 100, while synthetic base oils typically have a viscosity index in the range of 150. Next generation mPAO synthetic base oils deliver a viscosity index approaching 200, and that is a game changer. Using an mPAO based oil, you can now safely run 1 viscosity grade lower that you would using a conventional based mineral oil. If you are running a conventional 20W-50, just by changing to an mPAO based 10W-40, you can reduce start-up wear without sacrificing high temperature durability or oil pressure.

Armed with this knowledge of viscosity grades and viscosity index, you can select the right viscosity grade for your engine. In return, you can reduce the wear in your engine, improve fuel economy and make more horsepower.

At Driven Racing Oil, each of our synthetic racing and specialty perfromance oils utilize the high viscosity index mPAO base oil technology. These oils deliver dyno-tested and race proven power and durability to keep your engine running stronger and longer.

Using the Driven Racing Oil system of lubricants, Joe Gibbs Racing, has won 8 NASCAR championships and and over 100 races. If you have any questions regarding viscosity grades and selecting the correct viscosity lubricant, contact Driven Racing Oil at 1-866-611-1820.