[blue2000s]

Originally Posted by MNBoxster

Hi,

Sorry, but I don't agree.

The shear stress of a petroleum oil or other Newtonian fluid at a given temperature varies directly with shear rate (velocity). The ratio between shear stress and shear rate is constant; this ratio is termed viscosity. The higher the viscosity of a Newtonian fluid, the greater the shear stress as a function of rate of shear.

In a non-Newtonian fluid -- such as a grease or a polymer-containing oil (e.g., multi-grade oil) -- shear stress is not proportional to the rate of shear. A non-Newtonian fluid may be said to have an apparent viscosity, a viscosity that holds only for the shear rate (and temperature) at which the viscosity is determined. The shear failure point in most oils is between 4,000 and 8,000 psi. Source - http://www.lemd.com/motorsport/previous.cfm?id=19

Newtonian fluid - a fluid with a constant viscosity at a given temperature regardless of the rate of shear. Single-grade oils are Newtonian fluids. Multigrade oils are NON-Newtonian fluids because viscosity varies with shear rate. Source - http://www.oilanalysis.com/dictionary/default.asp?definitionsearch=xqxqxqxq222&alphasearch=N

Newtonian Flow - Occurs in a liquid system where the rate of shear is directly proportional to the shearing force, as with straight grade oils which do not contain a polymeric viscosity modifier. When rate of shear is not directly proportional to the shearing force, flow is non-Newtonian, as it is with oils containing viscosity modifiers. Source - http://www.chevron.com/products/prodserv/ehl/techterms.htm

I rest my case...

Happy Motoring!... Jim'99

I'm not trying to argue that a multi-viscosity non-synthetic motor oil is or isn't Newtonian, honestly, I don't know.

Your comment above suggested that the fact that the oil changes viscosity with temperature makes it non-Newtonian. This isn't what would make the oil non-Newtonian, it would be the fact that the fluid shear forces are not linear with the strain on the material.