Read my plugs? One totally different colour to rest. (PICS)

[zombo]

So I am changing my spark plugs, I took these out and one is a strange almost brown colour where the rest are white.

I am no spark plug expert so would like some light shed on what you think my spark plugs mean about the condition of the engine, in particular why one is a different colour to the rest.

Plugs 1-2-3-4

http://i55.tinypic.com/20ni2a.jpg

Plugs 4-3-2-1

http://i55.tinypic.com/1z2iz4p.jpg

[bennjamin]

http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

Look ok according to the above - note that the discoloured spark plug has oil on its thread further up than the other 3 - possible leak from O ring above or internal oil leak (valve stem seal etc) that is discolouring and altering the mixture in that particular cylinder

[tiksie]

I would say it's an O ring since the ceramics have more oil, unless a fubar valve stem seal can spit oil on to the ceramic ?