Spark plug readers

“You mentioned color on the threads, I looked this up and found nothing about it. How can thread color affect performance? I've changed many a plug and sometimes the threads were the same color as when I installed them sometimes a little darker.”

@Dan the man i had to quote you this^^^way because of how you replied above. @Newbomb Turk nailed it in post 7, and I will add to his reply. Changing plugs and reading plugs are two entirely different things all together. Trying to judge the tune up by looking at a plug with thousands of miles on it at various loads and rpm is a fool’s errand. Reading a plug for tune up must be done on new plugs. You make a hit, shut the engine off and read the plug. The color of the threads I mentioned above has to do with heat range and dialing in the plug’s ability to dissipate heat. It has very little to do with performance but can have a big impact on detonation and drivability. When the heat range is correct (or close to it) you’ll see 2-3 threads down from the tip colored (dark) after a pull, or at least that’s how I was taught by people much much more intelligent than me.