What causes carbon tracking on spark plugs

[PandaBear]

One of the 6 plugs in the Taurus was having a slight hint of carbon track from the center electrode on the insulator. As one of my previous post mentioned, with a life of 67500 miles on the plugs, the platinum tip on the plugs (both single platinum, one bank has platinum center and the other has platinum outer electrode) that came with the car have worn out completely. I suspected that there were misfiring and therefore poor fuel economy (20 mpg combined, 18 mpg city only and 22 mpg highway, compare to the previous history of 26 mpg combined when new).

I've never seen carbon tracking before on plugs, what is the cause? Could it be the wear on the plugs (i.e. bigger gaps) causing misfire, running rich, and therefore fouling?

 

[Kruse]

Originally Posted By: PandaBear
I've never seen carbon tracking before on plugs, what is the cause? Could it be the wear on the plugs (i.e. bigger gaps) causing misfire, running rich, and therefore fouling?


As you mentioned, or the ceramic has a slight crack or depression and the carbon deposited there when there was a misfire. Just replace with a good plug (my preference is Motorcraft or Autolite platinum) and it probably won't happen again.

 

[hate2work]

These plugs are typically only good for 50k or less. Have you looked at iridium plugs, they're only a few dollars more usually.

 

[mechtech2]

Carbon tracking is rare on a plug.
Carbon and oil fouling were once rather common, though.
Sounds like a physical crack in the insulator is the root cause.
Don't try and reuse that plug.

 

[PandaBear]

Originally Posted By: mechtech2
Carbon tracking is rare on a plug.


No wonder I couldn't find a photo of it other than a flat surface plug.

Thanks guys, I'll go ahead and replace them.

 

[punisher]

It is not really carbon tracking on modern plugs and wires. The spark, assuming an easier path to ground besides the plug gap, can travel along the plug's porcelain/inside of the boot and leave a track. This is from vaporizing the internal boot surface and depositing it along the path of the spark.

Off topic a bit, but I remember one Taurus wagon that came into the shop(no start) in which the customer reported that it was hit by lightning and died. I looked at the car and there were "carbon tracks" along the side glass at the rear of the car. No idea where the material came from to cause those tracks, but they were evident.

 

[PandaBear]

Originally Posted By: punisher
It is not really carbon tracking on modern plugs and wires. The spark, assuming an easier path to ground besides the plug gap, can travel along the plug's porcelain/inside of the boot and leave a track. This is from vaporizing the internal boot surface and depositing it along the path of the spark.


My track is in the combustion chamber side of the plug (firing tip along the porcelain). Nothing to do with the boot.

 

[punisher]

Well then, cracked porcelain, running rich, extremely high compression, plug too cold.