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Discussion Starter · #1 ·
I have about 20K miles now on my HKS M40XL plugs and decided to pull/inspect/clean them. These run one heat range hotter than the standard highly recommended HKS M45XL plugs and is what I really needed since with my setup, I was getting carbon fouling at about 6K miles with the M45XLs.

The gaps hadn't moved at all (still at 0.028") and they where slightly dry carbon fouled but not to the point of causing me any issues at all. They all looked about the same. They could for sure use a good cleaning however!

I cleaned them with CRC Throttle Body cleaner and a soft brass brush and towel being very careful to not leave any grit/dirt on them. I'll run them another 20K miles before I replace them if I can. Once cleaned up, they looked great. I've now got my "pep" back and the car idles very smooth!

Highly recommend these plugs. I got mine via David at the K5OptimaStore (special order, same price).
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