MadSci Network: Physics

Re: What types of vegetable oils are the best lubricants and why?

Date: Wed Jul 27 16:07:24 2005
Posted By: David Akerman, Staff, R&D Scientist, Madison Filter Ltd.
Area of science: Physics
ID: 1121827980.Ph

Hi Jane,

the job of a lubricant is reduce wear between two moving surfaces as far as
possible. With engines, which usually generate a lot of heat, you not only
have to consider the viscosity of the oil but also how this viscosity
varies with temperature - viscosity falls as temperature increases. In most
cases, viscosity will alter significantly over temperature so lubrication
oil in engines contain a mixture of oils of different viscosities to give
ideal lubrication in all weathers and when the engine is just turned on and
after it's warmed up.

Anyway, I've digressed slightly. With regards different vegetable oils I
found an interesting paper (from Slovenia of all places)
which looks at the different
viscosities of a number of vegetable oils. You don't need to read it
(unless you have a burning desire to!) but take a look at Table 2 or Figure
2 to compare the viscosities over a range of temperature.

As you suggested in your comment, the chemical nature of oils does
influence the viscosity and the authors report that, generally, the amount
of unsaturation (i.e. amount of double instead of single carbon-carbon
bonds) affects viscosity. So that, olive is the most saturated (Table 1)
and equally the most viscous. The reason is that viscosity within a liquid
goes up as there are stronger forces of attraction between the individual
molecules. With saturated (single C-C) bonds the molecules is more
flexible, therefore the closer the molecules can approach each other. With
closer proximity comes more entangelment and more effective van der Waals
forces. Unsaturated (double C=C) bonds are rigid and impose kinks along the
molecules so that these sections don't benefit so much from molecule to
molecule attraction.

Other factors which affect attraction are length of molecules (long equals
more entanglement - like your hair) as well as more impurities and any
partial oxidation, as seen when oils are heated for a long period of time
(more oxygen might mean stronger van der Waals forces).

But, to answer you original question, given the viscosity figures I don't
think you would notice much difference in the lubrication qualities of
different oils, however you would need to do testing for temperature
performance and longevity for more demanding jobs.

If you want to see if the figures in the paper correspond to observable
differences in your own vegetable oils, there are viscosity experiments at

Or there's a table of viscosity of various foodstuffs at the bottom of this

Finally, here's a company that sells lubrication / coolants made from
vegetable oil:


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