Changed them the first time at 70k, then today at 130k. Installed OEM Champion again. Stupid me I didn't mark each plug's cylinder but let me know what you think. Do my plugs indicate a healthy engine?

 

According to this website, my old plugs look pretty good, but still I am interested in your input.

Reading 101: How to Read Your Spark Plugs - OnAllCylinders

 

They look fine to me. They'd look pretty much like that had you held out to the manufacturer recommended 100K miles to swap, too (OEM plugs. My experience with another brand of more expensive plugs one time was far less life).

 

Thanks Mark. I am glad I changed them. Jeep runs noticeably smoother. The plugs did have noticeable wear such as smaller electrodes, slightly thinner prongs or whatever you call them, and thus larger gaps. Can't see that in the pics but it was time.

My original plugs at 70k were really worn out. Almost no electrodes left. I wouldn't leave them in for 100k.

 

My 2012 is gonna hit 95,000 miles this week. I'll be changing my plugs soon and I'll compare them with new ones like the OP did. I haven't done my research on here yet, but I assume buying oem plugs from the dealer is the way to go as opposed to buying some high tech aftermarket plug.

 

Champion oem's at the autoparts store are perfect.

 

What's the part number or the Champion number for the OEM plugs for a '12 JK?

 

RER8ZWYCB4 (Gap 0.043 in)

 

The engineers take the increasing gap size into account when they specify it for new plugs. This is unlike decades ago (pre-high voltage ignitions) when we pulled plugs, cleaned and regapped them.

 

It's still worth changing them earlier. These 3.8's aren't that fantastic. Those cylinders need all the help they can get and there is a noticeable improvement in how it drives after changing them. Given that these engines are prone to oil getting into the combustion chamber, a good plug makes a difference. Another 30k on those plugs would not be wise imo.