How Long Will My Iridium Spark Plugs Last?
November 8, 2011
A traditional iridium plug such as a Denso IK20 or NGK ZFR6FIX-11 both have iridium center electrodes, however the ground electrodes are a traditional nickel construction. The ground electrode will wear out first. Typically we have found you can expect 50-80k miles on an iridium plug. But plug manufacturers have to temper their projections as driving conditions and motor modifications differ. Additionally, because gradual wear will "round-off" firing points over time, the concentrated firing power and voltage requirement benefits will be reduced. Therefore, NGK gives them a life expectancy of 40-50k miles and Denso assigns a recommended replacement interval of 30k miles.
Both Denso iridium racing plugs and some NGK iridium racing plugs have iridium center and a platinum ground electrodes. If installed in a regular engine, they would likely last longer than most people keep their car (barring any motor problems that can cause premature plug death). But, these usually come in heat ranges too cold for an unaltered motor and are usually used in racing applications where all bets are off.
For the traditional automotive market, the longest lasting plugs are the NGK Laser Iridium and Denso Long-Life Iridium series, which have iridium center and platinum tipped ground electrodes. These OEM style plugs typically have special features designed for a specific engine and last 80-120k miles.