Lube-Tech Dr Edward Wright


Viscosity as a concept will be familiar to everyone. People talk of liquids as either being “thick” like treacle or “thin” like water though, more properly these should be described as being viscous and fluid respectively.


When it comes to lubrication, the viscosity of fluid that is employed to keep moving surfaces apart is probably the most important consideration if wear or excessive losses due to friction are to be avoided.


There are a very wide range of applications for internal combustion engines from cars and trucks, through to powering boats and trains and providing back-up electrical power for critical installations. However, fortunately, in almost all applications the viscosity of the engine lubricant is defined by a single, globally accepted, document known as the J300 standard published in the USA by the Society of Automotive Engineers (SAE).


This standard sets limits for two series of viscosity grades; those containing the letter W and those without. These are sometimes known as “winter” and “summer” grades which, although a useful distinction, is not completely technical correct.


Viscosity grades such as SAE 10W-40 and 5W-30 and the like will be familiar to anyone who buys oil for their car but what might not be so well known is that there are actually four viscosity tests which are used to define the range of grades. What may come as a surprise to many people is that three of these tests are described by the SAE as being “critical” specifications. This paper aims to explain the significance of critical specifications and the potential impact on formulators, manufacturers and users.


The four viscosity tests that are employed in the SAE J300 standard can categorised by the testing temperature and the degree of shearing to which the oil is subjected during the test. They can be represented as a grid – see Fig. 1.


PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


No.113 page 1


The Impact of SAE Critical Specifications to the formulating and manufacture of automotive oils


Fig 1. The 4 viscosity tests in SAE J300 Perhaps a few words on each of the four tests would be useful.


Two low-temperature tests are employed to define the limits of “W” grades.


The first, low-temperature cranking viscosity is measured by ASTM D5293 and has been found to correlate with the ability of an engine to start at low temperatures. The test is run at temperatures between -10o


C and -35o high rate of shearing during testing.


Low-temperature pumping viscosity (ASTM D4684) cools the oil to an even greater degree (-15o


C to -40o C) over an extended


period of time, designed to allow any wax in the oil to crystalize. Such waxy materials can produce a gel preventing the oil flowing into the oil pump and hence lead to oil starvation in the early stages of operation in winter conditions before the engine and the oil warm up.


LUBE MAGAZINE NO.142 DECEMBER 2017 33


C and subjects the oil to a


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