Spark-plug performance is one of the single
most important factors in maintaining gasoline
mileage and engine efficiency. It is estimated
that one spark plug firing improperly
can rob an auto of 15 to 35 percent of its fuel
efficiency. A spark plug consists of an electrode
encased in a ceramic insulator plus a metal
shell threaded to fit into the engine block. A
second electrode is attached to the shell.
The distance between the two electrodes is
called the gap and creates the spark. Gap settings
are specified by engine manufacturers
and should always be checked with a gauge
and reset prior to installation of the plug.
It is imperative that the consumer purchase
plugs recommended for use in his or her car,
based on the plug’s size and performance profile.
Just because it fits doesn’t mean that it
will work efficiently in the auto.
- Hot and Cold Plugs:
The terms “hot” and “cold” refer to the
ability of the spark plugs to dissipate operating
heat. They do not refer to the intensity of
the spark. As an engine runs, heat builds up in the
upper cylinder. If the spark plug cannot dissipate
its own heat, it can become hot enough
to ignite the fuel without the spark, causing
the engine to misfire. This is called preignition
and can cause serious damage to the
engine, if not remedied.
A cold plug will dissipate heat more rapidly
than a hot plug. Engine manufacturers will
specify heat range ratings for the engines.
Situations where a colder plug might be recommended
are when the engine is modified
for greater output, hauling heavy trailers, sustained
high speeds or heavy-duty applications
for exotic fuel uses.Hotter plugs might be
used for “oil burners,” light-duty applications
or continuous city driving.
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