The Goderich Signal-Star, 1978-11-02, Page 58Page 16
Plugs Need Change
Every 10,000 Miles
A spark plug may look
good to the casual observer
after 15,000, 20,000'or even
30,000- Miles.-;,-._._,, -. -
So why change plugs
after 10,000 miles of use
in your family car?
There's a good reason
according to experts_ The
10,000 mile change recom-
mendation is not actually
based on the fact that
spark plugs are "warn out"
in the strictest sense after
10,000 miles of service.
This figure — selected •
after extensive spark plug
life tests — Merely repre-
• sents..a safety factor be-
yond which plugs may
misfire under the sudden
demands of peak acceler-
ation or extremely heavy
load.
Gas Economy Drops
It also represents the
point at which gas econ-
omy begins to drop.i In,
addition -the car 3s harder
to start, power is lost in
passing. .
A spark plug is con-
" sidered worn out when it
reaches the point where it
is likely to misfire — re-
gardless of its appearance.
And, contrary to popular
opinion, misfiring doesn't
necessarily mean the plug
didn't create a spark. It
means simply that the
plug failed to ignite the
gasoline properly—wheth-
er a spark was produced
or not! •
A new spark plug with
the correct gap setting
needs about 5,000 volts to
fire. However, as the plug
remains in service, con-
stant heat and chemical
attack phis electrical ero-
sion cause the gan to be-
come wider, thus increas-
ing the amount of voltage
,. tp firethe plug...__ ...,...
Gap Gets Wider
Spark plug gap growth
occurs at a rate of about
.001 inch for each 1,000
miles of driving. Conse-
quently, a set of plugs that
has been in service for
10,000 miles generally will.
have gaps that are about
.010 inch wider than the
original settings and
higher voltage is needed
to make them spark.
And, this is only for
normal driving. Operating
the engine at very high
speed can decrease the
amount of coil voltage
available to fire the spark
plugs by 30 to 40 percent!
Accelerating to pass on a
highway may . practically
double the voltage burden,,,
'the spark plug.
Needs More Voltage
That's why misfiring is
first noticed while accel-
erating becauseit's here
that the plugs actually
can require more voltage
to produce a spark than
the ignition system is ca-
pable of producing -- es-
pecially if the plugs are
badly worn.
Remember, as plugs .re-
main in service, more volt-
age is needed to make
them spark. As the ignition
system ages, its ability
to produce high voltage
Lessens. If the point is
reached where the spark
plugs require more voltage
to spark than the system
can produce, the spark
plugs misfire.
The Champion Spark Plug Company Economy Rally, conducted in San Diego andthe
San Francisco area, began and ended at the gasoline pumps, where cars were filled
before and after the run. Gasoline wa, carefully measured to make sure accurate read-
ings of consumption were Fathered to determine. winners,f irly.v ......
Changing spark plugs at
10,000 mile intervals pre-
vents this from happening.
HANDLING SKIDS
If your car goes into a
skid on a wet or icy street,
turn the steering wheel in
the direction of the skid. Do
not jam on the brakes but
pump them gently.
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