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Diagnose this spark plug

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nedfunnell

Senior member
Hey guys,
This is the spark plug from the #1 cylinder on my V6 Camry.

Full-size: http://www.majhost.com/gallery/Ned/misc/img_1874.jpg

What's going on with that brown scorched-looking deposit there on the porcelain? That is, naturally, outside the combustion chamber. It seems ludicrous, but are combustion gasses somehow leaking through the plug and leaving those marks? It is hard, but a determined fingernail can scrape some of it off, as seen on the right side.

I'm sure it's a good idea to replace them (but honestly, internet, that's your answer to everything) but I am curious what this tells me about my engine. Any clues?
 
Well I had a spark plug blow apart a couple of weeks ago. The threading, bolt, and ceramic all separated. So I wouldn't think springing a leak is out of the question. Is it just the one plug? Only other thing I could see it being is scorched dialectic grease.
 
It's not combustion leaking but more likely simple discoloration from heat over time. What you're seeing doesn't look abnormal to me.
 
sparkplug_tech_036.jpg


sparkplug_tech_037.jpg


sparkplug_tech_038.jpg


http://www.ngkspark.com.au/sparkplug_tech.php#

Is that oil all over the threads?
 
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Ding ding ding! Thank you. Yes, that is oil on the threads- however, I am pretty sure that it is because the well for the #1 plug is right underneath the oil fill cap, and clumsy pouring of oil means some will end up sitting down by the plug.
 
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