Page 164 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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148 Automobile mechanical and electrical systems

Figure 2.132 Society of Automotive Engineers (SAE) logo

Figure 2.133 Castrol Magnatec multigrade engine oil. (Source: www.castrol.com , where you
can also fi nd a useful feature that recommends the correct grade for any vehicle by entry of the
registration number)

on whether it is being used to denote a cold or hot viscosity grade. Viscosity
is graded by measuring the time it takes for a standard amount of oil to fl ow
through a standard orifi ce, at standard temperatures. The longer it takes, the
higher the viscosity and thus the higher the SAE code.

Note that the SAE has a separate viscosity rating system for gear, axle and
manual transmission oils, which should not be confused with engine oil viscosity.
The higher numbers of a gear oil (e.g. 75 W–140) do not mean that it has higher
viscosity than an engine oil.
A single-grade engine oil does not use a polymeric viscosity index improver
additive (also described as a viscosity modifi er). For some applications, such
as when the temperature ranges in use are not very wide, single-grade motor
oil is satisfactory; for example, lawn mower engines, industrial applications,
and vintage or classic cars. However, multigrade oil is far more common. The
temperature range the oil is exposed to in most vehicles can be wide, ranging
from cold temperatures in the winter before the vehicle is started up, to hot
operating temperatures when the vehicle is fully warmed up in hot summer
weather.
A specifi c oil will have high viscosity when cold and a lower viscosity at the
engine’s operating temperature. To bring the difference in viscosities closer
Key fact together, special polymer additives called viscosity index improvers (VIIs) are
A specifi c oil will have high viscosity added to the oil. These additives are used to make the oil a multigrade motor
when cold and a lower viscosity at oil ( Fig. 2.133 ). The idea is to cause the multigrade oil to have the viscosity of
the engine’s operating temperature. the base grade when cold and the viscosity of the second grade when hot. This
enables one type of oil to be generally used all year. The SAE designation for
multigrade oils includes two viscosity grades; for example, 10 W–30 is a common