I've gotta say I'm very confused after reading what little spark plug discussion I could find in this forum, please accept my apologies in advance if I'm beating a dead horse here.

Which spark plug is the original plug, and which plug replaced it?

I'm seeing alot of conflicting information regarding which one is the original plug and which one is replacing it at dealerships.

Mine had RE6C-Ls in the car when I purchased it used from the dealership a couple weeks ago, and they looked like they were in good shape.

Since the car was averaging 8mpg :banghead: I changed the plugs. The leading plugs I purchased (which I was told was the "new design") turned out to be RE7C-L. The gas mileage nearly doubled after replacing the plugs.

What's confusing me is that what I'm seeing in these forums would suggest the opposite... does anyone remember early in the RX8s life which plug design was the original, and why it was changed?

Thanks!!

The 7s are the original heat range. Mazda installed the 6s when they did the starter/battery replacement with the belief that the engine would start quicker and foul less often for people who didn't understand that rotaries need to be hammered every now and then in order to run best.

Like what CRH saids.

All Rx8 came with 7 heat range plug, Mazda *think* that 1 step lower will prevent a lot of hot/cold start (and flooding) problems. Thats where the 6 heat range plug came from, and you can ONLY get them thru a Mazda dealership. While you can get the 7 plug anywhere else for 20s a pop.

but a 6 heat range plug should NOT make your car go 8mpg.

I had a 6 heat range plug for about 15 K miles(Engine no start TSB, I told them to do it, not like my car had any problems, starter, battery, and 6 heat range plugs)

I dont see any different. MPG about the same. anyway, I changed it out back to 7 heat range plug a little while ago.

6 or 7 doesnt really matter, if you dont have a problem with 7, stick with it.