spark plugs in the 21st century

[numboltz]

I'm an artifact left over from the 70s-80s etc and well remember the
points 'n plugs tune up era, where plugs really did deteriorate at short
mileage. I remember drawing an early Nova with a 250 for a tuneup, where
all 6 electrodes were well down into the porcelain [it ran great...well, it idled
great, just drove it into the shop] as a bad example, but in general in the
olden days the plugs told a story.

Nowadays things are much improved, of course, and I have often wondered
why plug change intervals are set at mileages that often seem arbitrary in that
plugs almost always seem almost as new. Now, I am thinking here in terms of
normal usage in stock vehicles. I know that with some engines, such as the
5.4 Ford family it is often recommended plugs are changed more often as a
way of dealing with galling issues. But what about engines, even aluminum
headed engines, with normal plug dimensions?

Finally got around to pulling the plugs on my 5.7 Mopar, 9 years old with
just over 100,00Km on it and the plugs look very good, gap has grown
about 0.008", came out easily. These are NGK copper core OEM style. So,
should I continue changing them out, or go for another 50,000?

[BLSTIC]

For what it's worth, this change was worth exactly zero noticeable difference, albeit on a way understressed 120hp 16v 2.0l engine

[swampbuggy]

The plugs you removed from the Mopar at 100,000 mi., were these cyl. heads alum. or cast iron ? Did the plug threads seem to have anything on them that would help them not to seize up as they were screwed out ? Mark H.

[bobalattie]

I replace a lot of spark plugs on fords.. the 3.5 ecoboost likes to have plugs replaced around 50k miles due to increased plug gap. It’s a noticeable difference. The first design 3 valve 5.4 is the same, 50k and it’s a noticeable difference when replaced. However the 2nd design 3 valve with the long threads on the spark plug I’ve seen go to 130k and couldn’t tell a difference when plugs were replaced.

Some of the older engines mid 90’s through 2010ish plug gap spec .052-.056, would wear plugs to above .080 and still run smooth, you’d never know they were worn, however I did notice more coil pack failures when the plugs were worn badly. Also carbon tracking on the external porcelain and inside the plug boot when plug gaps got too big.

[jake197000]

Seen many modern day engines with center electrode burnt all the way down.they seem to fun fine.they have so much spark potential it doesn't seem to matter much.might start a smudge harder.coils fail way more than plugs.yes I know a larger gap is harder on the coil but the plugs are still fine.l

[Schurkey]

Half the reason to pull the plugs at the OEM intervals is to get them out and re-apply antiseize before they "weld" themselves to the head threads.

God bless Iridium. I bought replacements, and yanked the plugs out of SWMBO's Trailblazer at 90K. They "snapped" as the threads began to turn, but didn't damage anything. The plugs looked so perfect, I tightened the gaps about .002, applied antiseize, and screwed 'em right back in. They didn't get replaced until 160K. No misfire "codes" ever.

[MadBill]

His Honda dealer changed out the plugs in my pal's 2007 Accord at 100,000 km and again at ~ 200,000. Then he read the manual and found that the factory spec was to leave them be until/unless a misfire code was set. He scrapped the car at over 500,000 klicks without ever setting the code.

[Alaskaracer]

In my old 2001 GMC with the 6.0L, factory plug replacement was at 100k miles...I worked in a shop that did emissions testing, so I put my truck on the scope. At that time, it was bone stock, and I'd just installed a new air cleaner. Ran it on the gas analyzer.. Mileage at the time was just over 50k. Changed the plugs with factory replacement (double platinum), and ran it again. While I felt no noticeable change in performance or mileage, there was a HUGE change in exhaust gasses......before the plug replacement, it was well within specs, but trending towards the higher limits....after just the plug replacement, it dropped to nearly the very bottom of the specs.....

So if you think that changing them doesn't make any difference when you do it early, you may not notice the change, but it does....I wish I'd have kept that report once it printed.