Postby smj999smj » Wed Nov 25, 2015 12:11 pm
I'm not sure what you mean by "fail more gradual." To me a "failure" is when the spark plug has a manufacturer defect, as oppose to a plug that is simply worn out because they have been used past its recommended service interval. Having worked 16 years for Nissan as a tech along with a number of years working for other shops, I have replaced an awful lot of NGK spark plugs and have only found one that actually "failed." It was a 95 Maxima and it was misfiring; it turned out the porcelain was cracked. I recall once working on a Mercury Villager with the Nissan VG engine and it had the original 30,000 mile NGK copper plugs in it at 148,000 miles and was still running well, albeit VERY worn (you could tell the original plugs on these as they were imprinted with both "NGK" and "Motorcraft" on them).
NGK makes the AC Delco iridium spark plugs and they have 120,000 mile service intervals on them, which is why I say, based on that fact and seeing what my plugs were like on my 08 Pathy, that they would probably have no problem going 120,000 miles on the NGK OE Laser Iridiums.
NGK G-Platinums, as are Iridium IX plugs, are NGK's economy line of platinum and iridium plugs, respectively, and to my knowledge do not come as original equipment on any vehicle. They are single platinum or iridium plugs that have a service interval of 60,000 miles.