Piston Slap: Who Will Iridium Me of This Troublesome Spark Plug?

by Sajeev Mehta

Published: July 23rd, 2009

piston slap who will iridium me of this troublesome spark plug

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?

Sajeev Mehta

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2 of 23 comments

Golden2husky on Jul 23, 2009

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)

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Rpn453 on Jul 24, 2009

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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