So, upon hearing the “good things” about the performance of copper plugs versus platinum and iridium plugs, I decided to get a set. My stock plugs were in need of replacements and at 10 bucks for a set of NGK coppers, I decided that it would be worth a try. The stock heat range copper plugs are the NGK BKR6E (stock #6962). I popped them in and they felt great. Just like a new set of plugs should. However, over the next 1000 miles or so that I had them on, I noticed my mileage beginning to go down. I usually average about 28mpg on the highway and with the coppers it went down to about 24 and below.
I don’t have any explanations for why it happened. This was on my daily commute as well. The only thing I can think of right now is the firing end design. Both the iridium and the stock platinum plug are fine wire designs. Don’t ask me for an explanation as to why it would affect the combustion, it shouldn’t make that big of a difference. But I saw it. The tank range went down a pretty good amount.
Power was pretty much exactly the same, except with this seemingly terrible mileage. I didn’t think it was the spark plugs until I decided to replace them with the NGK iridium fine wire equivalent, BKR6EIX. My mileage went back to my normal 28-29 highway.
The copper plugs looked like they were running very well when I pulled them. No deposits, even coloration, about as pretty as a spark plug could look. Maybe the coil packs just didn’t like them or something.
*The weather has been getting cooler recently, and mileage has gone up some more. This engine does not like the summer.
The BKR6E may not be exactly the stock heat range. The stock heat range may actually be a “7” for NGK plugs. Maybe BKR7E is the appropriate plug.