A story of 7 spark plugs.... 2018 Silverado 6.2L w/ 7600 miles

WeberKettleGuy · October 15

Hey all,

If you've seen my other posts, you'll know I've been chasing a couple issues with my centennial edition Silverado that are now fixed. The truck only has 7600 miles, and had a misfire a couple weeks ago that ended up being a bad spark plug. The GM dealer changed plug #4 and wire per the service writer and receipt. Misfire fixed. They recommended changing the rest of the plugs, as well as some injector cleaner since it's sat a lot. Here is my story.

After the original trans fluid was exchanged per the TSB last friday, and the shudder fixed, the truck still seemed to have a very minor miss here and there. I bought a bottle of injector cleaner (redline si1) and dumped it in today on my way to buy plugs. O'reilly's website showed two AC Delco plug numbers for my year and engine. 41-168 and 41-114. Per the website info, they have different heat ranges, and the 168 has a platinum ground electrode tip, the 114 has a iridium. I didn't see any other differences, doesn't mean there aren't. I called the GM dealer, and according to their computer, the only plug listed for my VIN is the 41-168. When I gave the parts guy the 114 number and asked what it was for, I was told it spec'd to 23 and newer 6.2L engines. I have no way to verify this, just what I was told. The guy beat O'reilly's price on the plugs, so I bought 7 and drove on home.

I stared with the passenger bank, changing all plugs from the top. I can see why they say removing the inner fender and wheel would be easier, But I managed to get them all from the top without too much issue. #8 did require a wobble/universal joint instead of the short extension. I highly recommend a magnetic spark plug socket if you don't already own one. I laid a folded painting drop cloth over the top of the engine and radiator for comfort. There was honestly much more room than expected.

When I pulled cylinder 8, and it was a different number, I started to wonder what was going on. so far, cylinders 2 and 6 had 41-168 plugs. I skipped #4 because it was changed..... allegedly. After pulling the drivers bank and finding 1,3,5,7 all had 41-114s in them. So I pulled #4, and it was a 41-114 as well. So yeah, I'm confused. I replaced all the plugs with the new 41-168 plugs, and reinstalled the 41-168 from cylinder 2 into cylinder 4 to make a matching set. My first thought is I was surprised to see oil on the threads, should I be at all concerned? Also curious about the tip of the center electrode. I did my best to take a close up picture. It's been a while since I've been in a gasser, is this normal electrode appearance after use?

Test drive went fine with no issues. I'd love to hear from you all on your thoughts as to why there are mismatched plugs in my truck. I could see the tech swapping plugs around to rule out a bad coil, but unsure why he would have replaced 2. Maybe he broke one? I'd also love to hear from anyone that could clear up the two different plug numbers and differences in each. More info on the truck, a different GM dealer replaced all the lifters last winter due to a collapsed lifter. Maybe that has something to do with the odd assortment of plugs. If a lifter fails, would or could that cause a plug to foul?

Looking forward to any information you all might have.

Thanks!

CamGTP · October 15

41-114 was the part number for my 2016, even in the owners manual it says that. It's exactly what I put back in there.

But GM did that on many of these trucks for whatever reason, they had 2 different part numbers for plugs. One being platinum and the other iridium plugs. Oil on the threads is very typical of all the newer LS or LT engines in my opinion. With the AFM/DoD system, some of these trucks burn oil and over time a little bit will work it's way on the threads of the spark plugs in the cylinder head. The tip on the electrode looks normal to me.

My guess is that the tech that did the lifter repair broke a spark plugs doing the work. The cylinder heads have to come off the engine to do the work and they likely broke a plug while doing, thus the other mis-matched spark plug.

WeberKettleGuy · October 15

8 hours ago, CamGTP said:

41-114 was the part number for my 2016, even in the owners manual it says that. It's exactly what I put back in there.

But GM did that on many of these trucks for whatever reason, they had 2 different part numbers for plugs. One being platinum and the other iridium plugs. Oil on the threads is very typical of all the newer LS or LT engines in my opinion. With the AFM/DoD system, some of these trucks burn oil and over time a little bit will work it's way on the threads of the spark plugs in the cylinder head. The tip on the electrode looks normal to me.

My guess is that the tech that did the lifter repair broke a spark plugs doing the work. The cylinder heads have to come off the engine to do the work and they likely broke a plug while doing, thus the other mis-matched spark plug.

I didn't even think to check the owners manual for plug numbers. I'm certainly going to keep after the oil consumption monitoring, if there is any. Oil catch can was installed last week with oil change. I'm happy to hear that the small amount i have is nothing to worry about.

Also didn't realize the heads had to come off to do the lifters.

Thanks for the response!

newdude · October 15

Not sure on the reasoning for GM changing plug numbers but yes, the original plug was 41-114 / 12622441, the current service plug is 41-168 / 19459511. Both are iridium plugs.

As for dirty plugs at low mileage, do you drive it? I see you only have 7600mi on a 2018, but have you floored it? Ever? I know DI engines can be dirty in the combustion chambers and all sometimes, but these modern low friction piston rings need some hard running time to seat and limit oil in the combustion chamber.

WeberKettleGuy · October 16

On 10/15/2024 at 10:47 AM, newdude said:

Not sure on the reasoning for GM changing plug numbers but yes, the original plug was 41-114 / 12622441, the current service plug is 41-168 / 19459511. Both are iridium plugs.

As for dirty plugs at low mileage, do you drive it? I see you only have 7600mi on a 2018, but have you floored it? Ever? I know DI engines can be dirty in the combustion chambers and all sometimes, but these modern low friction piston rings need some hard running time to seat and limit oil in the combustion chamber.

I've just recently inherited it a few weeks ago. I'm sure it was babied by my father in law. I've been running it pretty good over the last week trying to "clear the rest of the cobwebs" out of it.