I just had one ignition coil short out (cylinder 5, probably because it's swimming in oil from the leaking valve cover). I was wondering if there's any reason to change an ignition coil before it goes bad? Or do they stay good until they're not, meaning they're either good or bad but no in between or slowly going bad? I don't know if they've ever been replaced or if they're original still.
A somewhat related question: I've been told that iridium plugs are the best and that I should go with that, but I believe stock is platinum. Are iridium tipped better and if so why?

Thank you,

2003 G35 sedan 164k miles

 

I would just replace the one if it were me. Usually they stay pretty good if they are still working.

Stocks are double platinum. I'm honestly not sure if Iridium would be better in this case. Some choice to go iridium some chose to stay with double platinums.

 

From what I understand platinum plugs last a little longer, but iridium is a better conductor. Basically iridium produces more spark and a better burn of fuel or more power. I would guess the power would be less than .5 HP.

 

Just replace the one coil; with that component I'm pretty sure it's an all or nothing deal. I run iridium but I also change my plugs at a premature interval.

 

Awesome, thank you all for your help. I love this website!