From Chevron
https://www.chevron.com/-/media/chevron/operations/documents/diesel-fuel-tech-review.pdf
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Is the color of diesel fuel an indication of its quality?
The color of a diesel fuel is not related to its quality. As long as the fuel meets specifications,
it will perform well in your engine. The natural color of diesel fuels has traditionally varied
from colorless to amber. As refinery processing of diesel fuel increased to remove sulfur,
the color tends to get lighter and the diesel can change color. When it changes color, the
diesel is typically light in tone and can be green, orange, or pink. Sometimes it might
show a slight fluorescence when held up to light. Such a change in color does not affect
the quality of the fuel.
(vic comment - Cloudiness can indicate fuel quality issues.)
Does diesel fuel plug filters?
A plugged filter can be caused by several reasons. For example, if summer diesel is used
during cold weather, low temperature can cause wax crystallization, which can lead to
filter plugging. Dirt in the fuel or excessive microbial growth can also cause filter plugging.
The latter are “housekeeping” issues and are not directly related to the fuel itself.
Under some circumstances, a fuel with poor thermal stability can plug a filter. When the
fuel is exposed to the hot surfaces of the injectors, it forms particulates. If the fuel system
is designed to return a significant proportion of the fuel to the fuel tank, the particulates
are also returned. When the fuel is recycled, the fuel filter collects some of the particulates.
Over time, particulate buildup plugs the filter. This problem has been observed for
engines that were operating at high load and, therefore, engines that were operating at
higher than average temperatures.
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Anyone who wants to increase their knowledge of diesel should review the Chevron PDF. There's lots of good information there.
vic