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Be careful reading plug diagnostic charts
A vehicle
that is towing a trailer or caravan under heavy operating conditions has to work harder to pull the extra weight and very often
the spark plug will overheat. This is not due to any mechanical failure or that the cooling system is not big enough. It is simply because
the stock spark plugs, suggested by the manufacturer is to hot for this specific operating condition. The same can be said for any performance modification done to the engine and also if the engine is constantly being used for racing purposes.
The true importance of the heat range of
the spark plugs is a concept that is often not taken into account. So it is no surprise that even experienced mechanics are making
the incorrect diagnosis, because most of them are perhaps confusing a lean mixture with an
overheated spark plug as is the case if the vehicle is used under the operating condition mentioned at the start. The appearance of the firing tips look exactly the same. Some mechanics can not distinguish when the stock spark plug is too cold, like when driving at consistent low
speed, from when it has a rich mixture, because both have the same carbon fouled
firing tip appearance.
These incorrect readings of the spark plug are leading them to make the wrong decisions, either by carrying out repairs that are not required or
unnecessarily trying to adjust the air-fuel mixture. Instead of simply
choosing the correct plug heat range to suit the particular driving or operating
conditions that the customer will drive to.
Before you go off and start to change the heat range of your spark plug, consider all the possibilities that can be the cause to any one
of the spark plugs appearances. Is it due to a mixture, timing
misadjustment or other probable mechanical trouble, or is it due to the particular
driving habits and/or engine operating condition which may make it necessary to
change the spark plug’s heat range.
Some facts about spark plugs -
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You cannot get more power from an engine by changing spark plugs, you can only lose power by fitting the wrong plugs.
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The manufacturer of the plug has no bearing on engine power.
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The colour of the plug tip tells you nothing about the mixture condition, only when the correct heat range plug is fitted can you use the colour as an aid in tuning.
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Spark plugs with multiple earth electrodes offer longer service life but nothing else.
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