Auto Service World
Feature   April 22, 2009   by Allan Janssen

Precious metals

Consumers need earlier reminders about longer-lasting spark plugs.

Emissions, fuel economy, performance, and extended maintenance intervals are among the primary factors driving the development of vehicle technology.  And these factors have forced spark plug manufacturers to alter their products, too.

Every time a plug fires, a minute amount of material is removed from the electrodes. As mileage accumulates, the spark gap is widened, increasing the possibility of misfire occurring. This material depletion also affects the shape of the electrodes. The theory is, it’s easier for a spark to travel between sharp surfaces than rounded, worn surfaces.

Earlier spark-plug designs incorporated nickel alloy electrodes in their construction.  This worked satisfactorily with the ignition systems and emissions standards of the day. The introduction of distributorless ignition systems (DIS) imposed greater requirements on spark plugs. In a DIS, each spark plug fires twice as often as its conventional, distributor-style predecessor. This accelerates electrode wear, bringing about the need for more robust designs.

Platinum-tipped spark plugs have quickly emerged as the prevailing standard in many applications. Decreased wear and resistance to gap erosion are among the benefits. Maintaining gap integrity is crucial and platinum accomplishes this task very well indeed, greatly extending the plug replacement interval. Platinum offers another positive attribute: centre electrodes are now made smaller, thanks to platinum’s higher melting point and superior hardness. Electrons like to jump away from a finer, sharper electrode than from a bulkier, rounded one. This requires less voltage from the ignition system to ionize the gap, lessening
the chance of misfire occurring. This design also helps to improve cold starting and is more efficient in igniting leaner air fuel ratios.

Improvements continue

Meanwhile, as demand for fuel economy continues to increase and regulators impose tighter emissions standards,  manufacturers continue to extend maintenance service intervals. Factors such as displacement-on-demand systems and the
increased use of exhaust gas recirculation (EGR) continue to shape spark-plug technology into the future.

As well, there are now several manufacturers that realize the benefits of using other exotic metals to enhance the reliability
of the spark plug. For example, iridium is being increasingly embraced as this metal has an even higher melting point
and better corrosion resistance than platinum.  Iridium also allows for even further reductions in electrode size. This contributes
to easier spark generation, thereby making combustion possible when it comes to even the leanest air/fuel mixtures.
However, it’s worth noting that with certain vehicles, the factory-installed spark plugs have become very difficult to replace in recent years.

At first blush, spark plug replacement intervals of 100,000 km or greater might not seem like a positive development when it comes to maintenance opportunities for your shop. However, here are a few recommendations to help bolster service opportunities at your shop while at the same time helping your customers save money in the long run.

For starters, it’s terrific spark plugs last so long these days. But a plug can often seize in place. Attempting to change spark plugs at the specified mileage can sometimes result in expensive repair costs for customers. Seized plugs, broken plugs, and stripped threads are just a few of the problems. Therefore, it would be prudent to start compiling a list of the vehicle makes your shop
encounters that are known to develop such problems. As well, it would be advisable to create a proactive plugreplacement
schedule that ensures these problems are addressed. If you explain to your customer why you want to change his plugs at 60,000 km as opposed to 100,000 km, this will go a long way to assuring increased customer satisfaction down the road.

Even so, don’t set yourself up for problems. If a customer requests a plug replacement, don’t immediately start yanking plugs. Take into consideration the vehicle make and mileage. If the car is known to be problematic, be upfront and explain the ramifications to the customer before proceeding with the job.

Whenever you are performing maintenance on the ignition system, plugs are not the only candidates for replacement. I always make certain to replace ignition wires or cop boots depending on the application whenever I’m replacing plugs. Besides, a lot of the time, you end up destroying plug wires that are welded onto the plugs anyway. So, save yourself some grief and include wires or boots when you quote a tune-up.


Don’t go pulling plugs in order to inspect the plugs – this is a waste of time.  I liken it to looking at the dipstick to determine whether a vehicle needs an oil change. Indeed, there are technical service bulletins specifically advising against such a practice.  If a vehicle exhibits a drivability concern and you suspect an ignition problem, your scan tool and scope are your best bets for rooting out the cause.

Finally, only use replacement plugs.  Fancy, expensive plugs that aren’t required for an application won’t bolster horsepower
or improve fuel economy or, for that matter, add more pizzazz to your customer’s love life. Conversely, regular plugs in a platinum or iridium application will just wear out sooner. Bottom line: make sure the replacement spark plug is indeed the right one for the job at hand.

Todd Huggard is a licensed technician and a trainer with TechSupport West Diagnostics in Edmonton, Alta.

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