''Filters are the life of your engine. "
I think everyone would agree with that statement. However, there
are filters for oil, fuel, and air. Which one is more important?
In radioactive ring wear analysis test conducted with Southwest
Research Institute in the 1960's, it was discovered that the
engine cannot tell the difference in where dirt enters the
system. The wear rate is the same. So, all the filters are
The air cleaners provided on your chassis are heavy-duty dry
type filter media. Paper has been the media of choice for over
40 years. Although there are some synthetic media available, the
cost to benefit ratio is way too high except in special
applications. But, the paper used today is a far cry from those
of 40 years ago.
"The worst filter is a new filter." Say What!
That statement is also true. For air to flow through the fibers
of the filter media, it has to have holes in it. Make sense? If
the paper was made real tight, then the initial restriction to
flow would be too high, and the filter would become "loaded" too
quickly. So, the filter is made with "holes" so that air can
flow through it. I've always said that the best filter is a
solid wall. But, if you want air to flow through it, you have to
poke holes in it. As the dirty air flows through, the dirt
begins to build what is called a "dust cake" on the paper. The
dirt actually starts to be a filter itself. To get a little
technical, the filter starts at 99.0% efficiency (based on
SAEJ726 Test Code), and increases to 99.9+% as the "dust cake"
Why is that high efficiency important? Ask Cummins and Cat. They
will tell you that the main reason they can provide an engine
with the extended warranties and long life is because of improved filtration,
along with other technological advances. That's why they have a
specification for filters.
Air filters have other enemies than just dirt. Soot is the worst
and will cause the media to clog quickly. Water is a major
problem and requires special consideration.
"I don't change my filters often enough. "
That's probably what most of you think.
The fact is most air
filters are changed too frequently.
How's that, you say? The
filter on your chassis is designed and sized to provide long
life under the worst conditions. With the rear engine chassis,
the air intake will see more dust, water, snow, and ice.
Therefore, the filters are oversized to compensate. For normal
over the road service, your air filter should last 40-50,000
miles before it gets "dirty." However, the most important factor
for you would be the "shelf life" of the media. Since it is
cellulose, it has bonding agents that may over a period of time
tend to dry out and become brittle, particularly in high
humidity areas, coastal areas, and when you park the vehicle for
Although it is nothing to be alarmed about, we recommend the
filter be changed after two years of service even though the
restriction limit has not been reached. But, you also need to
monitor the filter, and this is done by use of the Filter Minder
indicator, a standard item on your chassis. The Filter Minder
has a graduated scale, with a yellow bulb that locks up at the
different restrictions as your filter gets dirty. Monitor it on
a regular basis. Do Not let someone convince you to change your
filter unless the indicator has reached the top 25" level. If
someone tells you they can look at a filter and tell if it's
dirty, I've got a job for them. I've been looking at
them for 22 years and I can't tell.
Remember the "dust cake"? The filter restriction only goes up
when the small "holes" start to become loaded with dirt. The
dirt on the outside of the paper doesn't tell you anything.
You'd have to look at the fibers with a microscope to tell if
they are dirty. That's where the indicator comes in. It measures
the restriction to flow or pressure drop in inches of water. The
gauge used for absolute measurement is called a water manometer,
but it's not practical to put one of those on your chassis.
The engine manufacturer specifies the restriction limits for
your engine, both "clean" and "dirty." The "clean" limit is
normally 12" and "dirty" is 25". Your owner's manual may specify
a different number, so check it out. As a precaution, if you're
driving in snow, I recommend you have a spare filter element
with you. One situation that may cause a false warning from the
indicator is if you drive in heavy rain or snow. The moisture
may cause the restriction to read high while the media is wet.
Reset the indicator, let the filter dry out, and monitor it to
see if it goes back up. The media will be fine once it dries
out. You can reset the indicator anytime you want - just push
the button on the bottom.
Air Filter Replacement Instructions