What to Consider Before Changing Your Spark Plugs

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By: David Opeyemi Shodunke

The recommended replacement interval for Standard Spark Plugs has typically been every 40,000 to 55,000 kilometres. But most of extended life plugs have special wear-resistant electrodes made of platinum, iridium, nickel yttrium or other exotic alloys that minimise electrode erosion. Such plugs can usually go 140,000 kilometres plus with little or no electrode wear. Even so, they may still be vulnerable to fouling if an engine has an oil consumption problem or spends excessive amounts of time idling.

Extended life spark plugs are a good upgrade for many engines, but may not be the best choice for an older engine that uses oil or even some performance engines.

According to one plug manufacturer, platinum-tipped electrodes run hotter than standard electrodes. This may increase the risk of pre-ignition and detonation in some turbocharged and high-performance engines. For such applications, a standard plug with a colder heat range might be a safer choice.

There are also a wide variety of electrode configurations from which to choose today. Each manufacturer claims certain performance benefits for their particular design. It may be reduced electrode wear or improved ignition reliability, or both. Such plugs are often marketed as “premium” or “performance” plugs, and may command a price which is quite different from the usual price. Some of these plugs (as well as standard plugs) also have multiple electrodes (two, three or four ground electrodes).

A spark plug with more than one ground electrode will still only produce one spark per ignition cycle. But with four paths from which to choose, the likelihood of getting a good spark to, at least, one of the ground electrodes is multiplied for improved ignition reliability. Having more than one ground electrode also distributes the wear to minimise electrode erosion and growth of the spark gap over time. Such plugs also experience a self-cleaning effect because the sideways path of the spark helps burn deposits off of the insulator.

Are premium plugs worth the extra money?
They are; if they can provide extended plug life; reduce the need for maintenance or improve overall ignition performance. The plugs in many front-wheel drive cars and minivans with V6 engines are very difficult to replace. Installing extended life plugs can almost eliminate the plug change hassle for good. Likewise, performance plugs that reduce misfires can enhance performance for a smoother running, cleaner, more fuel efficient engine. No spark plug can create power out of thin air, but improved ignition reliability can minimise any horsepower loss due to misfire.

What to do before changing spark plugs:
When changing spark plugs, wait until the engine has cooled to remove the plugs. The engine should be at or near room temperature, and not hot to the touch. This is very important with aluminum cylinder heads because they reduce the risk of damaging the threads in the cylinder heads when the plugs come out (aluminum is a much softer metal than cast iron).
Most threads on spark plugs for engines with aluminum heads are either pre-coated to reduce the risk of thread damage, or the plug shell is made of a nickel alloy. If the plug shell is black or plain steel, however, you should put some anti-seize to the threads, and reduce the applied torque by about 30 to 40 per cent.

Do not use anti-seize if the plug shell is nickel or has been pre-coated. Anti-seize acts like a lubricant and may allow too much torque to be applied to the plugs, damaging the treads in the cylinder head.

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