By on July 23, 2009

TTAC Commentator don1967 writes,

What’s the deal with these platinum/iridium-tipped spark plugs? Is there any reason to go through the (sometimes very high) cost of dismantling half of your engine to replace them every 100,000 miles if the car is running fine? Also, what do you think about periodically loosening and retightening them to prevent seizing . . . does that ever actually happen?

Sajeev replies:

For your first question, I smell a Seinfeld reference coming on. But I won’t go there. Instead, know that platinum plugs usually go 100k miles, which combined with metal timing chains, made for great marketing propaganda (circa 1996) when Detroit wanted to trump those pesky CamCords that needed new plugs and timing belts well before the magic 100-grand mark. Great idea, but it didn’t work.

And here’s what little I know about Iridium plugs: they give stronger spark during leaner air/fuel ratios and generally respond well to serious engine modifications. They don’t last as long as platinum plugs, so I don’t recommend them to your average motorist.

Don, when it comes to changing plugs, I am a big fan of RTFM. Not because I take twisted pleasure in ripping off intake manifolds (and wiper motor assemblies, vacuum lines, sensors, etc) to reach the back plugs on a transverse-oriented V6, but because old spark plugs can’t perform like new. I’ve changed several (neglected) cars with platinum plugs with over 100k and they felt faster, idled smoother, and got 1-2mpg better economy. And if I really cared to find out, I suspect the re-tuned motors spit out far less emissions for Mother Nature to deal with.

Last question: I’ve never considered this loosey-tightey regiment you mention. I use a dab of anti-seize on the plug’s threads before installation. Removal (when the engine is cold) is no problem afterward.

Bonus! A Piston Slap Nugget of Wisdom:

What’s true for grocery shopping also applies to cars. If (like me) you perform tune-ups in your own garage, take note: don’t buy the little ketchup packets of anti-seize at the parts counter. Instead of spending $1.00 on almost nothing, get a bottle of the real thing for an extra $6. And be set for life. How great is that?

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23 Comments on “Piston Slap: Who Will Iridium Me of This Troublesome Spark Plug?...”


  • avatar
    johnny ro

    I love my Permatex copper based anti seize. Going on 5 years on the little bottle and I use it wherever I should.

    I have graphite based as well. Seems they have a different compound for whatever different metals you are attaching.

    My Bosch platinums lasted short time so I stopped buying. The center electrode melts and spits itself out. This is with no mods on my cars and no racing.

  • avatar
    LennyZ

    Here’s a question I’ve gotten all kinds of answers to. Do you change your torque values when using anti-seize? Torque higher? Torque the same?

  • avatar
    philbailey

    I once had to explain to an old lady how she had four (equivalent of) 9 m/m bullets pointed at her lower torso and how the engine had to come out, to change spark plugs, because the back four plugs had never been changed and the steel part of the plug had completely disappeared.

    Spark plugs left in place too long DO seize up, anti seize or no anti seize – it happens. Then the hole has to be drilled out and re-threaded using an insert. Generally speaking, there’s no need to remove the head if the drill/reamer is well supplied with grease to catch the steel debris.

    If you possibly can, it’s a good idea to ease and re-tighten every couple of years or 25000 miles.

  • avatar
    tiger260

    Good article.

    I just changed the plugs in my Toyota V6 for NGK Iridium plugs which are supposed to be rated for 60,000? I used “copaslip” which is a copper-based anti-seize grease (a well-respected British product but available through the classic car suppliers like Moss Motors). The original platinum plugs had been in there for well over 100,000 miles I believe and they came loose easily so I presume someone must have paid attention to greasing the original fitment (possibly at the factory). Of course, getting the wrench onto the damn plugs in the rear bank of cylinders is the tricky bit! I wouldn’t fancy having to loosen them and re-torque every 25,000 miles if I could avoid it?

    By the way – nice Henry II / Thomas Beckett reference…. Are you sure you’re not all Brits?

  • avatar
    OffCamber

    I buy coppers and change them every other year. Overkill, I know, but it makes me feel good and it only takes 10 mins for each of my cars. I use copper anti-seize and torque to recommended specs.

  • avatar
    TEXN3

    This is interesting…my current car is the first one that can theoretically go “100k miles” on it’s Ford-sourced platinum plugs. Car is nearing 60k miles, so I think I’ll add a plug change to the list of items to take care of.

  • avatar
    Lumbergh21

    Change them at least as frequently as the manufacturer recommends, the car manufacturer that is. I have noticed a marked improvement the two times that I have changed out spark plugs. It may have been psychological, but I doubt it. As an added bonus, you can look at the sprak plugs and get an idea of what has been going on in the combustion chambers over the past several years. Probably not as important as when engines were carbureted (versus modern fuel injection), but yoou could learn something like one cylinder is running rich because it isn’t firing consistently or running lean because the injector is messed up.

  • avatar
    GS650G

    I go 40K on plugs. They are cheap and on my car (escort) easy to change. I do use a torque wrench to tighten them.

    Buddy of mine had a car that refused to start, turned out the plugs were so bad it would not run. The engine computer compensated for the bad plugs right until they would no longer work. That has good and bad points I guess.

    Saw a plug break off at the base once. Left the thread and center electrode in the head. I cranked the engine briefly and the center electrode shot out. Then I used an easy out (big one!) to remove the shell from the head. So they can break off in the head.

  • avatar
    dubtee1480

    Loctite makes an anti seize in a beautiful format: applies like a twist-up glue stick. No mess, no waste and I’ve had the same stick for 4 years now. If you buy platinum, avoid the Bosch plugs, most cars I saw them on while working at AutoZone had less than optimum results with them. And they are NOT a replacement for the OEM platinums.

  • avatar
    William C Montgomery

    Last year in inspected my ‘05 Jeep Liberty’s plugs (ye olde style NGK’s) at about 35K miles. They were carbon-encrusted fried nubs and the gaps were wildly off. They were also baked into the head and I held my breath with each plug until the threads freed up.

    Then I checked my ’01 Honda Accord’s plugs that had more than 101K miles on them. The platinum-tipped plugs screwed out of the head with the greatest of ease, were perfectly gapped, and looked like they came right out of the box. I put ‘em back in (knowing that I was getting the entire engine, timing belt, water pump, etc. serviced soon).

    No question, I put platinum tipped plugs in the Liberty with plenty of anti-seize.

  • avatar
    Subifreak

    It depends on what specific iridium spark plugs we are talking about…for example, OEM Iridiums say from NGK are much different than their ‘IX” branded plugs that will last barely 30 – 50k miles due to their construction & amount of actual iridium material used….compared to their OEM’s at 100k+ miles before needing replacement (the prices of each plug reflect that). I steer clear of all Bosch plugs period. I’ll only use NGK or Denso’s personally.

  • avatar
    dubtee1480

    My mother’s 2001 Silverado came with factory iridium’s. The ACDelco iridium plugs are actually Denso’s in sheeps clothing. Her plugs finally kicked it at about 115K – 130K.

  • avatar
    slavuta

    My experience tells me that one shouldn’t follow 100K miles spark plug replacement.
    Why:

    – It can seize
    – It can rust on outside
    – It gets fragile with time and can break off

    Speaking only about 100K tuneup cars, I’ve seen:
    – rusted plugs, which could not be removed with a socket.
    – plugs that would break during removal
    – plugs that stuck to wires and caused wires tear during removal
    – Plugs that seized completely
    – plugs with cracked ceramic
    ———————————–

    !!! Check ALL plugs !!! One can be in great shape, the other can be rusty, etc.

    My suggestion is to replace those at least at 60K or 5 years.
    I can also recommend that if the plug is not coming out easily, one should spray a loosener spray first and wait for 10-20 minutes. Once plug is loose, carefully wipe/vacuum around, so no liquid or dirt goes into cylinder.
    I also noticed that it is easier to pull the plug on the hot engine and not cold.

    And this is true. You can pull the plug and inspect it. Even clean it. Re-gap it and put it back in if it is in good condition.

    Now, back to regular plugs – those are so cheap that one can replace every 30K and no need to maintain them.

    Anti-seize goes long way. Even cheap one.

  • avatar
    George B

    Just put a new set of NGK platinum spark plugs in my 99 Acccord at 100k miles. Easy job with spark plugs on the top of the heads vs. on the side of previous OHV cars I owned. Like William C. Montgomery observed, the old OEM spark plugs looked good when removed from service. Checked the plugs several years ago and since they looked good back then, I put the OEM plugs back in and ran them to 100k miles. Wish Honda used better automatic transmissions to go with their engines.

  • avatar

    Screw the iridiums and go straight to the new “La-ser” plugs!

  • avatar
    gslippy

    Yes on the 100k plug change. I’ve done it on two Caravans so far (96, 98), but I also spent the money to change the fuel injectors at the same time. Changing the injectors adds only minutes to the job, and I have found bad ones in the process (leakers at the pintle). The work is difficult (plug change), but the results are rewarding.

    Yes on antisieze, also.

    I’ve had good luck with Bosch 2-fork platinum plugs.

  • avatar
    eggsalad

    Silly gasser drivers. My car has no such silliness as spark plugs. I do intend to clean my injectors soon, as the car nears the 250,000 mark.

  • avatar
    guyincognito

    I’m running NGK iridiums now and I’m happy with them. I change them every year. Of course, my plugs sit at the very top of the engine in a nice neat line with easy access. I6 FTW!

    Even if it were more difficult, I would recommend at least removing the plugs to look at them every 2 years. Reading the plugs can tell you alot about how your engine is running and if there are any serious problems developing.

  • avatar
    friedclams

    Don’t forget the wires! I once changed the (original) wires on my Olds and left the plugs alone… the car ran way better. It’s amazing how clean FI cars run versus the carbureted old days.

  • avatar

    Using the NGK spec’ed by BMW, found they tossed a check engine light in 87k miles. Replaced and found 15 hp.

    I’d follow the manual. Over 100k or so, cost per mile is very,very low.

    Of Course, if I had one of those cars which required removing the engine to get at the rear plugs, I might feel differently…about the company and engineers, not the spark plugs.

  • avatar
    don1967

    I remember the horrors of changing the last two plugs on each side of my 1980 Pontiac V8… Ray Charles with broken thumbs would have had a better chance.

    The Honda and Nissan four-cylinder successors were a dream come true; twenty bucks and ten minutes was all it took to perform this basic maintenance. But the dream would not last. Every V6 techno-wonder since then has been a nightmare. I never get farther than reading “remove intake plenum” before my eyes glaze over with visions of pushing the car into a lake.

    I greatly appreciate the collective wisdom of TTAC’s best and brightest, but the divergent opinions only confirm that I was Born to Lease.

  • avatar
    golden2husky

    Spark plugs really do tell the story about the health of your engine. Do yourself a favor and keep them in order as you remove them. And yes, they most certainly can seize in the head. Some engines are notorious for this and for snapping in the head (looking at you, Ford Mod motors)

  • avatar
    rpn453

    These iridium plugs still looked good after 127k miles in a Corolla:

    http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1379334&fpart=all

    It really depends on the vehicle and the specific plug.

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