Add me to the list: 2013 Lariat with 52k now. Already had the system recharged 2k ago. It is at the shop again today.

 

What are you referring to? This is a thread about a 5.4 misfire.

 

My fault. I was on another thread and I replied to the "related threads". Sorry, disregard please.

 

I too have been studying on this, and I understand the length of the porcelain from plug tip back upwards to where it spreads to outer plug nody is the determiner of heat range. But all that is inside the lower barrel, any plug when installed and torqued in place in a head has it's body thus virtually become as one with the head metal … be it aluminum or cast iron, etc. It then transfers heat to that head. I believe it remains the length of the porcelain inside the barrel that controls heat transfer rates from plug tip to plug body, and thus head … thus setting or controlling heat range at plug tip. A shorter path leads to cooler plug tips, longer leads to hotter.

I don't think deposits on the plug well wall and lower plug barrel will affect heat … but if bad enough, excessive buildup may well pose a risk to a new plug being snugged into place.