[rayr2018]

Was replacing plugs and noticed 3rd coil was off white almost burned looking, kind of an oil/rainbow slick to the rubber end cap which was slightly morphed from heat i presume. was curious by looking at picture attached if anyone could advise if this is in fact a sign of a bad coil or something else. i already replaced but was just curious. i dont like that new coils are all black so wouldnt be able to determine if color changing from environment factors are at play as easily.