Which spark plug should I buy?
They are plenty of choices, so pick the right spark plugs for your particular vehicle
Car makers advertise a 100,000 service interval on spark plugs. Following that advice can cost you. Technically speaking, a spark plug can last 100,000 miles. But that doesn’t mean it’s efficient during its whole life. The ugly truth is that a 100,000 mile plug that has 80,000 miles on it is 80% used up! The gap has widened and it’s not producing as hot a spark. You’re getting less pickup and poorer mileage. Worse yet, you may already be experiencing power robbing (and catalytic destroying) misfires. The bottom line is that you don’t save ANY money by putting off spark plug replacement. In fact, you’ll actually save money by changing them out at 80% of their rated life. Spark plugs are cheap and new ones are the best way to increase engine performance and gas mileage. Finally, leaving spark plugs in for the manufacturer’s rated life may actually cause problems as corrosion builds up and “welds” the steel plugs to the aluminum cylinder heads.
Change them early! And install new spark plug wires at the same time.
Go shopping for spark plugs and you’ll see a dizzying array of brands. Worse than that, you’ll see several different types of plugs for every application—single platinum, double platinum, iridium, yttrium, double electrode, quadruple electrode, and split electrode. Here’s the way to make sense of it all and buy the right plug for your vehicle.
First, let’s talk about the precious metal plugs like platinum, iridium, and yttrium. The whole point of using precious metals is to reduce the erosion (wear) caused by high voltage sparks. Car makers started using these precious metals to extend the service intervals between spark plug changes and to decrease the misfire rate seen in conventional plugs. In a traditional ignition system, the spark jumps from the center electrode to the side electrode. In those applications, manufacturers weld a small disk of platinum to the tip of the center electrode. Makes sense so far.
But then the car makers started using a different type of ignition system called a Distributorless Ignition System (DIS). In a DIS design the spark jumps from the center to the side electrode during the compression cycle, and in that piston’s partner cylinder (which is on its exhaust stroke) the spark jump from the side electrode towards the center electrode.
The spark jumps backwards in the exhaust stroke cylinder because that’s the return ground path back to the coil. You don’t need to understand the workings of the whole system, just the part where the spark jumps backwards from side-to-center. In a DIS system, car makers specify a DOUBLE PLATINUM plug to prevent erosion on BOTH of the electrodes.
Looking for a bit of a marketing edge, Bosch invented two spark plug designs, the +2 and the +4 design. The biggest difference in their plugs is that the spark jumps sideways towards the side electrodes. Bosch claims that this design produces better combustion because the point of ignition is not shielded by the electrode. The reason for the multiple electrodes is simple—they are known as sacrificial electrodes. As one of the electrodes begins to wear to the point where the gap is greater that the gaps on the remaining electrodes, the spark will choose another electrode that’s closer. Thus, the worn electrode is “sacrificed,” never to be used again.
Some people have reported performance issues with the Bosch side-fire plugs. My main objection to these plugs is that the gaps are preset at the factory and DO NOT match the spark plug gap recommended by the manufacturer. The theory behind side-fire electrodes is that by opening up the combustion area below the center electrode, the fuel/air mixture actually makes it easier for the spark to jump the gap. I don’t believe that this theory always works well in practice.
The queen bee of all plugs is the newer iridium style. This plug is supposed to give the best performance of them all. Iridium has a much higher melting point (700 degrees higher than platinum) is 6 times harder than and 8 times stronger than platinum, and conducts electricity better than any of the other precious metals. Therefore, it lasts the longest. However, it has a price to match. Depending on the brand, iridium plugs run from $8-15 per plug.
Whether you choose single or double platinum, or make the move to iridium, here’s what’s most important when choosing a plug. Some plugs come with a gap that is NON-ADJUSTABLE. That’s fine if the gap is EXACTLY what your car maker recommends.
Plug manufacturers used to recommend applying a small dab of anti-seize compound on the threads. Not anymore. Spark plugs these days have an anti-corrosive treatment that makes anti-seize obsolete. Also, it is VERY important that you use a torque wrench when installing new plugs. If you over-torque a spark plug in an aluminum head, you can destroy the threads— a VERY expensive mistake! If you under-torque, the repeated compression cycles can loosen the plug and blow it right out of the hole—taking the threads with it. Again, another very EXPENSIVE mistake. Some torque specs are as low as 10-ft/lbs. So it’s really easy to overtorque them. Check your service manual or the spark plug manufacturer’s specs for the right torque. Also, reduce the torque by 10% if you’ve applied anti-seize compound on the threads.
Here are the top brands of spark plugs:
Autolite XP Xtreme Performance plugs (this is an iridium tipped plug with platinum tipped traditional “J” side electrode)
Autolite HT Revolution Plugs (uses a “U” shaped electrode) Autolite Double Platimum (uses a platinum disk at the end of the center electrode with platinum tipped traditional “J” side electrode)
Champion EON Spark Plugs (with traditional “J” side electrode)
Champion Iridium Spark Plugs (with traditional “J” side electrode) Champion Double-Platinum Power Spark Plugs (uses a platinum disk at the end of the center electrode with platinum tipped traditional “J” side electrode)
Champion Platinum Power Spark Plugs (platinum tipped center electrode with traditional “J” side electrode)
ACDelco Iridium Spark Plugs (this is an iridium tipped plug with platinum tipped traditional “J” side electrode)
ACDelco Professional Platinum Spark Plugs (uses a platinum disk at the end of the center electrode with platinum tipped traditional “J” side electrode)
ACDelco RAPIDFIRE Platinum (single platinum, ridges on center electrode direct current towards platinum pad and traditional “J” side electrode)
NGK Laser Iridium (laser welded iridium tip on center electrode with laser welded platinum disk on traditional “J” side electrode) NGK Laser Platinum (laser welded platinum tip on center electrode with laser welded platinum disk on traditional “J” side electrode)
NGK Iridium IX (fine iridium wire center electrode with traditional “J” side electrode)
NGK G Power (fine platinum wire center electrode with traditional “J” side electrode)
NGK V Power (center electrode has a “V” cut in it. Spark always like to jump from a sharp clean edge. As one edge wears, the other takes over)
Denso Iridium (0.4mm iridium tipped center electrode makes it the smallest center electrode on the market. Targets the spark better. “U” groove on side electrode to keep a sharp edge landing area)
Denso Double Platinum (platinum tip on center electrode with platinum disk on traditional “J” side electrode)
Bosch Platinum IR Fusion (combination iridium/platinum center electrode with 4 yttrium side-fire electrodes)
Bosch Platinum +4 (platinum wire center electrode with 4 yttrium side-fire electrodes)
Bosch Platinum +2 (platinum wire center electrode with 2 yttrium side-fire electrodes)
Bosch Platinum Plus (platinum wire center electrode with 1 yttrium “J” style side electrode)
© 2012 Rick Muscoplat