The humble spark plug has come along way over the many years. Once spark plugs were cleaned and gapped every service with replacement done every couple of services. Now we have spark plugs lasting 100 000km!
The big change is the material used in the spark plug such as platinum or iridium. This allows the spark plugs to wear at a much slower rate which is why they last so much longer. The down side is the cost. These generally coast between $20 – $40 each. But over the life of a vehicle the cost is less as they don’t need to be changed very often. Also with many vehicles access to change the spark plugs is very hard, some even needing the inlet manifolds be removed. This means more labour which equals more cost. So the less we need to change them the better.
With that all being said, it is still important to change the spark plugs at the set intervals set be the manufacturer. If they are not replaced conditions such as running rough, poor performance, high fuel consumption and misfires can occur.
The main pics attached shows new vs old fouled spark plug out of a Mazda RX8. The pic below shows two used spark plugs, standard vs iridium, you can see the difference in the electrode. The Iridium is pointed while the standard is square. The pointed style gives a more consistent spark while standard plugs will wear the electrode down and round off the electrode causing inconsistent spark patterns.