Leading or trailing plug difference
 

Hello - Can anyone tell me the difference between the leading and trailing plugs? And - how often do they tend to go bad? Thanks! Sprout

Gidday, Dont get them mixed up .The Trailling plug has a hotter spark than the Lead one.If you look on the block beside the plugs you will see it marked "T" or
"L" to identify them, also the lead spark plug is longer than the trailling plug so dont put the wrong sort in ,otherwize 'CRUNCH'

Their failure can be caused by different things. Generally over time they can lose effectiveness as they wear but they are irridium which is one of the ultimate materials used in the ignition game. The environment in which they live can be very tough, especially in a rotary engine where they are firing very frequently. As Wren pointed out, they are a different heat range to each other; however the trail are colder than the leads, not the other way round.

Paul.

What do you mean "crunch" I just bought one and they had the plugs reversed and pull the plugs out and see no sign of contact

consider the source i.e either fake or not-informed news bro’ …
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It might have fouled more than normal, but I don't think it would do lasting damage. There could be secondary problems like poorer fuel economy and more load on the cat over long term, so depends how long it was like that. But we're not talking huge differences.