Don’t Get Fooled by Cold Kinematic Viscosity Oil Ads

A Motor Oil’s Kinematic Viscosity Is Only a Factor When the Engine is At Operating Temperature

Kinematic viscosity is a measure of motor oil’s resistance to flow and shear due to gravity. It’s an important measure of a motor oil’s flow rate when the engine is warm. It’s measured in seconds-to-empty. In other words, it’s the time required to flow a fixed volume of oil by gravity through a calibrated orifice or capillary at a controlled temperature. That value is then converted into centistokes (cST) or square millimeters per second. But it’s a useless term when talking about how oil moves in a cold engine. Here’s why.

Oil companies try to scare car owners by showing kinematic viscosity flow using frozen oil

Oil companies freeze oil and then show you how much longer it takes to pour conventional oil out of a beaker. But Kinematic viscosity has nothing to do with how long it takes oil to flow in a cold engine

Cold engines don’t move oil by gravity. If you use the recommended oil in your engine, the oil pump can easily move it when the engine is cold. And an oil’s pumpability is much different than its gravity flow.

When talking about cold oil, it’s Absolute or Dynamic Viscosity That’s Meaningful

To get an idea of how motor oil performs in cold weather, you want to know its absolute or dynamic viscosity. That’s a measure of how well an oil performs when being pumped during cranking; the two most critical measures when talking about how oil performs when cold.

Kinematic viscosity is measured at 40°C (100°F) or 100°C (212°F), while absolute viscosity is measured at a different temperature for each SAE viscosity grade.

In other words, Kinematic viscosity is a measure of oil when hot (minimum 100°F) not when cold. So, when oil is expressed as Xw-XX, the XW is it’s absolute or dynamic viscosity and the XX is its kinematic viscosity.

©, 2020 Rick Muscoplat