You take your car in for an oil change. The work is almost
done when the technician comes out to talk to you. He’s
holding your air filter and PCV valve and recommending
that you replace both because they “look dirty.” Without missing
a beat, he explains how critical the air filter is to the efficient operation
of your car. He tells you that a clogged air filter, or one that’s
nearly clogged, can easily cost you 10 percent in gas mileage. With
gas prices going through the roof, he adds, replacement will probably
save you more than the cost of the filter. Plus, a dirty PCV
valve, well, that’s never a good thing. Then he waits for your decision.
It’s tough to make up your mind about a $25 air filter and
an $11.95 PC-whatchamacallit valve when you don’t know what
to look for.
It’s not difficult to check the air filter and PCV valve yourself.
Here’s what you need to know:
Air filter check
First, ignore the dirt on the leading edge
of the air filter pleats. All air filters accumulate
dirt on the leading edges in as little
as a few thousand miles. Yet most last
for about 12,000 miles. You want to know
how much dirt has penetrated deep into
the pleats. To test the true condition of
your filter, hold a shop light behind it. See
how much light passes through the inner
pleats and compare yours with the three
sample photos below. The filter shown on
the left is totally clogged and cost the
owner a fortune in wasted gas. The filter
in the middle shows a clogged area, but
the rest of the filter has decent light transmission.
It’s borderline, and the owner
could probably squeeze 2,000 to 3,000
more miles out of it. It should be replaced
at the next oil change interval. The filter
on the right shows how much light passes
through a new filter.
Click Image to enlarge.
1. Follow the black plastic duct to the air filter box. Unscrew or unsnap the
latches. Remove the filter. Note that the screen always faces the engine.
The pleats face the incoming air.
Click Image to enlarge.
2. Hold the
filter over a
shop light and
compare it with
the photos above. Reinstall
or replace.
The PCV story
The PCV (positive crankcase ventilation)
valve is a one-way valve that recycles
crankcase gases back into the engine to
burn. A plugged PCV valve can result in a
rough idle and poor mileage. Worse, it can
cause costly oil leaks. Always follow your
manufacturer’s replacement recommendations.
And never replace a PCV valve simply
because it “looks dirty.” All used PCV
valves look dirty.
Photos 1 and 2 show
two ways to check its real condition.
1. Remove
the PCV
valve from its
grommet.
With the
engine off,
shake the
valve. If it’s
good, you’ll
hear a solid
clicking
sound.
2. Or, check it in place with the engine running.
Pull the PCV valve from its housing and place
your thumb over the PCV valve opening. You should
feel it click. If the click sounds or feels mushy, replace
the valve.
