Stick with iridium spark plugs
This isn't related directly to the Theta platform, but I wanted to share it here anyway. The car here is a 2009 Impala, with 170K miles.
My sister-in-law was here recently on spring break from college, about 1000 miles away. I was prepared to work on her car as she's had a check engine light on for 8 months since she was last here (P01174). Ultimately, her issue was that the computer had gotten way off on the ethanol calculation and was reading it as 55%, but she's only used 10% fuel. However, while I had the car I did a few other things like O2 sensors and cleaning the MAF sensor and throttle body. She said her dad had changed the spark plugs some time ago. On a whim, I wanted to pull one and check the condition. I had one **** of a time getting them out even with soaking them in penetrating oil. That was my first clue. The second clue was that the plug wires were AC Delco. The last clue I had about this plugs was that she thankfully had a full service history of the car. After getting a rusty stuck plug out and going over all the documentation, I'm pretty **** confident that these plugs and wires are factory original.
The book calls for a .040 gap, and after 170K miles, these plugs were still amazingly between .048 and .050 gap. Most platinum plugs I've used seem to need gapped (or replaced) at around 50K miles. Copper definitely doesn't last anywhere that long.
That's a pretty good testament to why GM chose iridium and why you should too. Change your plugs once at the service interval of ~100K miles, and it's likely the last time you'll need to change them.
2017 Equinox 3.6L Premier AWD
2011 Silverado 1500 LT, 5.3L 4X4