The ground electrode does wear considerably faster than the center iridium electrode. They may last and function for much longer than 7500 miles, but they still wear and deteriorate gradually over time. Misfiring is very detrimental to the catalytic converter in the stock muffler... You should also make sure the coils are well grounded.
Hello Invader and others,
I am due to change my plugs according to the manual - having completed 24,000 kms now.
I came across a youtube video on replacing spark plugs here where the user says Iridium Laser plugs which are a step up from Iridium plugs by NGK provide a life of between 60,000 - 100,000 miles:
Question: Are the stock OE Plugs Iridium IX or Regular Iridium?
Here is what NGK says on their Facebook page (in a comparison to IX): This is a good question, the Laser series plugs are designed for a longer service interval of 100,000 miles or 160,934km. This has to do with it being a “DFE” or dual fine electrode; harder metals reduce the gap erosion process.
The IX series is a single fine wire, meaning that there is only Iridium on the center firing electrode, where as the Laser has this on the ground and firing electrode. IX are approximately a 50,000 to 60,000 mile service interval or 80,467km.
If our plugs are regular Iridium from the factory, then I guess their service intervals are even lower than the above two?