Why don't my spark plugs last 150,000km?



That depends on what you mean by "last." Is it possible for a spark plug to function for 150,000km? Under ideal conditions, yes. Spark plugs made with platinum or iridium coupled with today's high output ignition systems may be able to create a spark sufficient to fire the air/fuel mixture in the cylinder for 150,000km . But , there may be some severe consequences to waiting for the 150,000km mark. One is the additional burden placed on the ignition system by worn spark plugs. An ignition system will only produce enough voltage to fire the spark plug, typically 5000 volts at idle to perhaps 15,000 volts under acceleration. Some modern ignition systems such as DIS (Distributorless Ignition Systems) or COP (Coil-On-Plug) systems can produce as much as 50,000 volts!

As a spark plug wears, the gap becomes wider and the electrodes more rounded. Both conditions require more voltage to create a spark. So, if your worn spark plug requires 40,000 volts to fire, the ignition system will do it. But producing that kind of voltage will take its toll on the ignition system. The question becomes, "Would you rather replace four, six or eight spark plugs at $5 each or four, six or eight ignition coils at $90 each?"






There's an even greater reason to replace spark plugs before 150,000km. They have been known to seize in the cylinder head if left in that long. If that happens, you could be looking at a $2000 repair bill to remove the heads and replace the spark plugs. Will that happen to you? Maybe, maybe not. Are you willing to take that chance?

The 150,000km spark plug is nothing more than a 80,000km spark plug that the carmaker's marketing department calls a 150,000km plug. It sounds impressive to say that their car doesn't need a "tune-up" for 150,000km. It's really a marketing driven claim, not one based on sound engineering. Manufacturers often add stipulations to the 150,000km interval that's in the owner's manual, but is often overlooked.

The most prudent thing to do is to replace standard spark plugs every 60,000km. Platinum and iridium plugs should be replaced every 80,000km.

Any more questions?

Direct them to mike@robinsonautomotive.com