What is the difference between absolute viscosity and kinematic viscosity?

**Viscosity determines oil film thickness. Kinematic viscosity is just a convenient attempt to estimate the film thickness of the oil, but it provides very little. If oil is non-Newtonian. Its meaning is less important.

Many common lubricant formulations and conditions produce non-Newtonian fluids, including:
• Viscosity Index (VI) Improver Additive - Multi-component mineral-based engine oils (except natural high VI base oils) are formulated with elastomeric additives that densify at low temperatures and expand at high temperatures in response to increased fluid solubility. Since this additive molecule is different from the main oil molecule, it behaves non-Newtonian.

•Water contamination - Oil and free water do not mix and do not react chemically. But in some cases, they combine to form an emulsion, like the mayonnaise discussed earlier. Anyone who has ever seen oily coffee with cream can attest to this. Although it may seem counterintuitive, water contamination actually increases kinematic viscosity when water is emulsified into oil.

•Thermal and oxidative degradation by-products - Many thermal and oxidative degradation by-products are insoluble but are carried by the oil in stable suspension. These pauses produce non-Newtonian behavior.

•Soot - Commonly encountered in diesel engines, soot is a particle that causes colloidal suspension in the oil. The oil's dispersant additive is designed to prevent soot particles from agglomerating and growing to promote the formation of colloidal suspensions.

If one were to measure the viscosity of one of these commonly encountered emulsions or colloids with a variable shear rate viscosity meter (such as ASTM D4741), the measurement would decrease as the shear rate increases until it stabilizes point. If this stable ** viscosity is divided by the specific gravity of the fluid to estimate the kinematic viscosity, the calculated value will differ from the measured kinematic viscosity.