5.3L Spark Plug Gap Changed to 0.040"??

[2Kchevy]

About 3yr. ago I changed the factory plugs on my stock 2000 5.3L w/ NGK Iridium IX plugs. At the time these plugs came w/ an 0.060" gap and my Haynes manual (bought ~5yr. ago) also has an 0.060" gap listed for the 2000 5.3L.

I was just looking today at what plug is now recommended and was surprised to see every replacement plug now has a 0.040" gap on NGKs website.

Anyone know why the recommended gap changed from 0.060" to 0.040"?

Should I now go back and gap my TR55IX plugs from 0.060" down to 0.040"?....they only have ~22Kmi on them.

Thx.

[FullsizeRST]

i dunno i noticed that when i got them also but i went ahead and stayd .060

[GasGuzzler]

When GM swapped from the old school platinum to iridium they changed the spec to 0.040". The ACD 41-985 plugs are pre-gapped and should not be changed in the traditional manner. NGK's are cheap so just gap them to 0.040" and throw them in.

[2Kchevy]

If the change from platinum to iridium caused the change in the gap, then it still seems odd that now even platinum and copper aftermarket replacement plugs are gapped to 0.040" as well....at least the plugs I see on RockAuto.

There must be something else behind moving to 0.040"....smoother idle?...longer plug life?...

On RockAuto the NGK IX series iridiums are $6.90ea. and the ACD 41-985 iridiums are $5.89ea.

Thanks.

[oleshifty]

I'd still check gap on the ACD 41-985, i've seen a few be off slightly.

I think the change in gap might be more towards change in fuel grades (ethanol and what not). Not 100% sure. If you're n/a i'm sure it doesnt matter much, and if you're FI, you need a different gap anyway.

A closer gap theory wise, should increase hp slightly, but also raise the chance of detonation/knock, which would kill any gains.


I have the a/c platinums. Gap'd at .040. Changed factories at 100k miles, and I have about 45k on these.

[GasGuzzler]

That's a different NGK than most people run and that ACD plug price is almost half what the suggested retail is. Mighty good internet shopping job. I'm sure you're correct about better idle or something but it's probably not longer life. My originals had no wear at 75K...my Blazer got plugs after 200K miles with no signs of erosion on the stock platinums.

If I were to guess I'd say it's the man trying to reduce emissions...

[GasGuzzler]

There are specific instructions from GM to not check or adjust the gap on the 41-985 plugs. The center electrode is very small and delicate and very easy to damage. Merely sliding a feeler gauge in the gap can wear or chip the iridium.

Not that I believe all that just saying...

What's funny is the bulletin might have been canceled as I just looked for it and could find it

[oleshifty]

oops, o well, they work fine

[molitor]

i tried to change the gap on my 7 dollar NGK plugs, i broke the first electrode off. After that, i was really, really careful and managed to open them up to .060, truck runs awesome by the way, throttle response went back up

[2Kchevy]

well, I guess I'll keep 'em at 0.060" unless I hear a compelling reason not to.