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March - April 2017
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two dissimilar types of oil, and carbon insolubles from thermal
failure can all darken oil. There is also a possibility that the oil dark-
ening is due to a photochemical reaction from sunlight exposure.
Measuring color is based on a visual comparison of the amount
of light transmitted through a defined depth of oil. This can be done
with a predefined test method and instrumentation or a subjective
view of the oil with reference to a color gauge. In either case, there
may be a number of variables to monitor for quality results.
The ASTM D1500-07 test method can be used to compare the
color of an oil sample to a glass slide. This test is used in lubricant
manufacturing for quality-control purposes. It is performed using
a standard light source to match a sample to a glass slide. Values
for the glass range from 0.5 to 8.0 in 0.5 increments. If the sample
falls between two colors, the higher number is reported. If no color
gauge is available, the oil color is compared to a previous sample
or a new oil sample.
It should be noted that color is added using dyes in some cases
to help identify the type of lubricant, such as red for automatic
transmission fluid. Nevertheless, an oil with a specific color should
never be assumed to be a certain type of oil. It is also important to
remember that there is no particular oil color that would require
an oil change.
If you have a question for one of Noria's experts, email it to
editor@noria.com.
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All rights reserved. Images: AV10013, AV19512, AV19520, AV13207, AV01056, AV11797.
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