I have had extremely poor service life out of my NGK spark plugs in my 2019 Mercury 200 HP outboard. In the first 60 hours of use the dealer had to replace the NGK LKAR7C-9 plugs twice. For those of you having similar issues with your V6 Mercury outboards using the NGK LKAR7C-9 spark plugs I have a solution for you. I replaced the NGKs with Champion 991 (REA8MCX) plugs and put over 150 hours on them with NO issues whatsoever. I have inspected them at very regular intervals and they look perfect. If you want to run an Iridium plug Autolite XP5683 are a crossover to the NGK plug. I may try these at some point. Several of my fellow boaters are making the switch to the Champion plugs due to the poor service life with the NGK plugs.
