I have a chance today to remove and examine my plugs since I'll be a t a shop helping a friend work on his car. I've got about 11K miles on my 8, and I want to see how much buildup is on them. If they are dirty, how should I clean them? Any advice from folks who have a favorite product? Just soap and water? Thanks

 

I use lacquer thinner.

 

I've used brake cleaner and a small steel brush in the past... worked great. You just need something that can break down the carbon deposits.

 

Don't use a metal brush on the insulator; it can leave traces which become a conductive path and lead to misfires.

 

How about, replace them?

 

^^ In general, I tend to agree. Plugs should settle into a mode where enough self-cleaning happens to keep them viable. If that isn't happening then the engine or electrical needs work or perhaps needs different plugs (heat range). On the other hand, an isolated flooding incident can severely foul the plugs and it's possible they can be cleaned well enough to function and return to service, where the normal self-cleaning will bring them back to a normal state. Depending on your willingness to experiment, it may be worth it to save $120 on a set of plugs. I'd use a piece of wood to gently remove any serious gunk, and then an evaporating solvent to remove excess oil. Again, a metal implement such as screwdriver or wire brush is going to risk leaving conductive metal traces on the insulator.

 

I don't disagree- I religously changed my Miata's plugs every 10k miles, but the rotary plugs are so damn expensive I can see why you might want to clean them up. I'm curious what mine look like... I believe I do a good job keeping them clean via the 9k rpm carbon vaporizer routine, but I haven't checked them yet.

 

Why are they so expensive? What so special about the RX8 plugs?

 

The conductor tip is nearly flush with the butt-end of the plug due to the design of the rotary chamber... a normal plug would protrude into the chamber and would contact the apex seal as it passed over. I believe they also have Iridium electrode tips for long life and better conductivity. I ran NGK Iridiums in my Miata, and they were about $36/ set... which is expensive as hell as plugs go. I don't know why the rotary version is that much more.

There are some good pics of them in this thread:
https://www.rx8club.com/series-i-tech-garage-22/plugs-after-20k-miles-55005/

 

Remember, black deposits are bad; light brown deposits are good. That is, light brown that indicates a nearly complete burning of the fuel-oil mixture and the best you can hope for, whild black indicates an incomplete burning of the fuel-oil which is leaving deposits of the unburned mixture as a carbon deposit on the insulator. The center insulator is what you should be concerned with since a coating of carbon on that will result in the reduction or elimination of the spark bridging the gap between the points. Of course, wet, whether with gas or oil, is bad but easy to remove with a little solvent spray.

If you have dark deposit on the center insulator, try a little emery paper folded into a small enough piece to allow you to get down into the gap between the insulator and the body of the plug. Lightly rub the emery paper on the insulator to remove all the dark carbon material you can, then spray with a solvent. This is an old two-stroke, dirt bike trick I used many times successfully.

 

I used an old toothbrush and carb cleaner. They shined like new and none of the Iridium got scraped off.

CRH

 

Be Careful!!! Charles' idea is probably the safest. I have read in several places that the iridium plating can be damaged very easily. Probably why some Mazda TSB's simply say to replace rather than attempt to clean them.