Originally Posted By: robertcope
If you google a bit, you'll read from Castrol that they've been working on lower viscosity oils in the cars for a number of years.
"About five years ago, we really pushed to reduce the viscosity,” explains Arnfield. “The lower the viscosity, the less drag in the engine, which means we have more usable power.
That's true to a point. But like everything else, it has limitations. I saw an interview with Ray Evernham once. This was back in his glory days with Jeff Gordon. He said at the Super Speedway, 500 mile races at Daytona and Talladega, they used a thin oil for qualifying, but ALWAYS ran a much thicker weight race oil during the race itself. He said if they didn't there was no way the engines would live for 500 miles at those RPM's and temperatures. Now, what he meant by "thinner and thicker" you be the judge.