To do this job well, the oil must be viscous enough to prevent metal-to-metal contact, yet not so viscous that it's hard for engine parts to move. Starting with the right oil is the first step; changing the oil regularly is the second step.

Even the very best oils cannot prevent intermittent metal-to-metal contact in certain engine parts and operating conditions. For example, at start-up and in new and rebuilt engines, metal surfaces are relatively rough, which increases pressures and squeezes the oil film so that it is only a molecule or a few molecules thick. The result is high friction and high wear. This most often occurs on the top piston rings (which have a limited oil supply), the valve train, and parts of the rocker arms. Here, the antifriction and antiwear additives in Pennzoil motor oils adhere to engine parts, helping to reduce friction and protect the engine.