Spark Plugs 4.0

No. It’s a spark plug...don’t over think it. Iridium last longer than copper which is why I changed to iridium. I have run mine for 30K and I can tell zero difference. I ran copper when drag raced a 68 firebird and currently run copper in my KTM 2 stroke because I change the plugs more often.

 

As long as your gas mileage isn't any worse, I'd let them go. Years ago, I replaced plugs in a GMC pickup I had. It had the platinum plugs in it and that was OEM but they were eight bucks each. I didn't want to spend fifty bucks on plugs so I bought iridium or something of the sort. It ran smooth but seemed down on power. After a couple of fill ups, I noticed my gas mileage had dropped a couple of miles per gallon.
I went back and spent the fifty bucks and replaced them again. Then it was back to normal.

Gas mileage check is a good indicator.

 

I have been getting 420 miles per tank since purchased new. Now have 202k miles on original plugs.

 

I have a 2006 Tacoma 4x4 with the 4.0. I put NGK iridium plugs in it not long after I got it in 2018 at 95k miles. After about 3-6k miles I'm not sure. My truck started to run rough so I bought so Denso double iridium plugs cause the NGK jumped gap and were bot firing properly. So if you go iridium I strongly suggest Denso. Jmo

 

I stick with "standard" plugs and swap them every 30K miles. That gives me a chance to inspect the plugs to see how my truck is running. It's not a bid deal, since I don't mind swapping plugs that often.

But if you prefer to minimize your routine maintenance, go ahead and switch to iridium plugs. They should be good for at least 90K miles.

 

Be careful if you buy plugs on Amazon or eBay.. I never knew people counterfeited those. I purchased oem sensor plugs on eBay and within 10k miles I had a center electrode brake and cause a misfire.