What is the difference between A leading spark plug and a Trailing spark plug, are they interchangable and what will it do if you interchange them, also does anyone have any pics of them so I can see the difference.

Justin

 

the only diff is one number in the plug serial number. and they should also have an "L" and "T" written on the plugs.

the heat ranges are slightly different.

if you swap them the car will still run.

leading are the lower ones

 

I think the leads have two blue stripes around the ceramic. Or maybe the trails do? They match to the original ngk wires though. The difference is the heat range.

 

IF that fails, the plugs have a handy little "L" and "T" on them. Wonder what those stand for?

 

L=leading=lower
T=trailing=top

easy way to remember