What’s New In Spark Plugs

Spark PlugsIridium is the newest innovation in spark plug technology.  Iridium has the potential to challenge Platinum as the metal of choice in spark plugs.  When Bosch first introduced Platinum spark plugs in 1985, they’re heat and wear resistance were unmatched.  These plugs can go upwards of 100,000 miles without being replaced.  Platinum plugs cost between two and four times more than regular ones, but their much longer service life makes them worth it.  Long-life platinum plugs also created a whole new segment for premium replacement spark plugs in the aftermarket. Prior to this, parts stores could only offer standard replacement spark plugs, or some type of “performance” spark plug with an enhanced electrode design that reduced misfires and improved performance. A lot of “hocus pocus” science and marketing hype surrounded many of these electrode designs. Yet in spite of the claims that were being made for some of these plugs, none could match the longevity of platinum plugs.

Iridium: The Challenger

In 1994, the first Iridium plugs hit the market as an alternative to Platinum. Why Iridium? Because it has a higher melting point, is six times harder than platinum, and is more corrosion resistant than Platinum and most other metals.

The Cost Issue

The momentum toward iridium spark plugs also is being fueled by its relative cost advantage compared to platinum. Currently, iridium is still the cheaper metal, costing around $1,085 an ounce compared to $1,480 an ounce for platinum. Though iridium is actually a much scarcer metal than platinum (or even gold), its price has been less subject to market volatility.
The price of platinum has bounced around from a low of about $1,300 an ounce in 2009 to a high of $1,900 an ounce this past summer. Iridium, by comparison, had been selling for $440 an ounce in 2009. But with rising demand, its price was driven up to more than $700 an ounce in 2010, and it doubled again in 2011. Whether or not iridium can maintain its price advantage over platinum remains to be seen.
Industrial demand is driving the cost of iridium more than it is platinum. Nearly one-fifth of the world’s limited iridium production is currently going into spark plugs. By comparison, only a small percentage of platinum is going into spark plugs. Nearly half of the platinum that is produced annually is being used to make catalytic converters, and another 20 percent is going into jewelry.
The amount of platinum or iridium that is actually required to manufacture a spark plug is quite small. A tiny button or piece of wire made of iridium or platinum alloy is welded on the tip of the center and ground electrodes to prevent electrode erosion and wear. Even so, when multiplied by the millions of spark plugs that are produced every year to satisfy the demands of both the vehicle manufacturers and aftermarket, the cost of the metal really adds up.

Replacement Plugs

Different spark plugs work better in different applications. On Waste Spark systems, each pair of cylinders shares a common ignition coil. Cylinders that are opposite one another in the engine’s firing order are paired so their spark plugs share the same coil. On these types of applications, spark plugs with dual precious metal electrode designs (platinum or iridium) are typically required because they receive more wear than in the other systems. With Coil-On-Plug (COP) ignition systems, each spark plug has its own separate ignition coil mounted directly over the spark plug. The type of spark plugs used with this type of ignition system are not as important because the plugs fire with the same frequency as those on an engine with a conventional distributor. It’s the same story with Coil-Near-Plug (CNP) ignition systems. Single platinum or iridium plugs can be used without loss of service life. Plugs can be swapped out for plugs of different brands since most suppliers sell spark plugs that aren’t make or model specific. There’s no reason not to switch brands unless the customer prefers to stick with what they have.


An important difference to look for when choosing a spark plug is the plug shell plating. The plating helps the plug keep from sticking to the cylinder head after 100,000 miles. Using anti-seize on spark plug threads that are going into an aluminum cylinder may seem like a good idea, but it is NOT recommended. One reason why is that too much anti-seize on the threads can squish past the threads and foul the center electrode, causing the plug to ground out and misfire. Another reason is that anti-seize acts as a lubricant and reduces friction when the plugs are tightened. This increases the risk of overtightening the spark plugs and possibly damaging the plug threads in aluminum cylinder heads. The best advice is to look up the plug torque specifications for the application, and to use a torque wrench to tighten the plugs.

Spark Plug Maintenance

Spark plug service intervals haven’t changed in recent years. It’s still 100,000 miles for most late model vehicle applications with long life platinum or iridium plugs, or as much as 120,000 miles for some. These are factory recommended replacement intervals, and it’s not unusual to see spark plugs that are still performing just fine at much higher mileages. But there’s a risk if the plugs are neglected for too long. As the electrodes wear, the voltage required to fire the plugs continues to go up which will eventually lead to misfires and possible damage to the ignition coils and/or spark plug insulator boots. The OBD system will detect ignition misfires and turn on the Check Engine light.By the same token, a 100,000-mile service interval does not guarantee the plugs will last that long. Plug life can be shortened by frequent short-trip driving and idling, as well as internal engine problems that increase oil consumption (such as worn valve guides or piston rings). Fouling problems may require more frequent plug changes. On all engines, especially those with aluminum cylinder heads, the spark plugs should be changed when the engine is cold or only slightly warm to the touch. This will reduce the risk of damaging the threads in the spark plug holes (because aluminum is a softer metal than cast iron).
Replacement spark plugs don’t necessarily have to have the same electrode configuration as the original spark plugs, but they must have the same thread diameter, pitch and length, same type of seat (beveled or flat with a gasket), and same approximate reach into the combustion chamber. Always follow the application listings to make sure your customers get the correct replacement plugs.
Most plugs come pre-gapped from the factory, but the gap may not be correct for all of the applications the spark plug fits. For this reason, the electrode gap should always be measured with a plug gauge and adjusted as needed to the setting specified on the underhood emissions decal. Avoid using tapered coin style gap tools to adjust plug gaps as this may damage the precious metal electrodes.