Thus, Zakarian says, researchers have come up with “hundreds of different equations” that allow users to measure a few data points and extrapolate an oil’s performance under a specific set of conditions. This works well as long as an application falls within the parameters under which the profile was created, but it offers limited knowledge of how the oil will perform under different conditions. The next best solution after “test everything” is to include a viscosity versus temperature profile in an oil’s specification. Some mechanical parts are very large or otherwise unwieldy, such that conducting standard rig tests is impractical. However, that approach requires a significant investment of time and money. Testing specific oils with specific engine components would be the most direct way to find this out. Specifically, it is important to know how a specific lubricant formulation will behave over the entire range of temperatures it might encounter during operation. “Pretty much anybody who works in the oil industry at some point or other has probably had to do the calculations,” he adds-parts designers, OEMs, lubricant formulators and even end-users.ĭespite the difficulties in untangling these interactions, trends toward faster, hotter engines and tighter tolerances require a more sophisticated understanding. “Most people end up having to know something about viscosity,” says lubricant formulation specialist and STLE member Jack Zakarian, principal at JAZTech Consulting.
For example, thicker lubricant films keep contacting parts well separated, but they also can increase friction and drag, which increases temperature in the contact area, which thins the lubricant film. Lubricant viscosity, temperature and operating conditions all interact in complex ways, some of which are poorly understood. Though it is widely known that oil-based lubricants are less viscous at higher temperatures and more viscous at lower temperatures, calculating a precise viscosity presents a formidable challenge. Calculation methods based on physics and chemistry could aid in the intentional design of lubricant formulations.Viscosity index is often used as an overall indicator of an oil’s quality, but this assumption is not always accurate.Equations that describe viscosity changes with temperature have various strengths and limitations.
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