Just some background: I bought my 2005 RX-8 two years ago with 64,000 km. I had a compression test done (as part of the purchase agreement) and the results were excellent (between 8.2 - 8.6 both rotors @ 280 RPM) and was told that this was still a very strong engine but the plugs were POOCHED! So I installed a set of the correct NGKs and also decided to premix going forward with 400 ml of MYSTIK JT4 2-Cycle Synthetic Blend Sea & Snow Engine Oil (non TC-W3) per tank (50 lt) of premium (approx. 125 to 1). All was well for about a year and a half then I slowly noticed some misfiring mostly at cold start-ups and also normal idling. Then a couple of O2 Sensor related codes showed up! I had put on 10,000 km (6,000 miles) by then. Service records from the original owner showed that plugs, wires and coils had NEVER been replaced. Rather than mess around, I just bought the full set from MazMart and swapped everything out last fall and cleared the codes. Surprise! It runs like a dream but especially has a different note at speed and is noticeably more responsive. Hard to say if the fuel consumption will improve but that'll be a bit of a bonus. Codes have not returned after a couple of tanks more fuel so fingers crossed.

So I decided to do a bit of checking on the old parts and definitely feel that the T1 coil (rotor 1 trailing plug) was likely failing as the resistance measurement was different than the other 3 coils (don't recall exact #). Also the T1 plug was WAY sooty compared to the mid-brown colour of the other three. My thought is that with only 10,000 km (6,000 miles) on them, these plugs should be good as a spare set and have lots of service left in them if I just clean them up. I've read that carb or brake cleaner and a toothbrush work well as long as you don't damage the iridium coating. I am happy with the 125:1 premix as there is no visible smoke and only a touch of tailpipe soot. Opinions greatly appreciated.

 

Sure, those plugs have some life left in them if carefully cleaned.