<VV> Hot vs. Cold plugs...

[Secular]

  Just about everyone has heard that plugs have heat ratings, and are 
  called "hot" or "cold" types. Some people think that means the plug 
  either makes the engine run hot or cold, which is completely wrong. 

  The amount of heat a plug brings into an engine due to the electrical 
  sparks is so small it's insignificant. The amount of heat a plug removes 
  from an engine is also small.

  Those ratings - "hot" and "cold" - mean simply this: a plug becomes very 
  hot in an engine, so we say it's a hot-running plug - or just hot. Another 
  plug doesn't reach such a high temperature, so we say it's a 
  cold-running plug - or just cold...

  ...The main difference between hot-running and cold-running plugs is the 
  length of the insulator nose...

  ...Fouling due to a too-cold plug is much better than pre-ignition due 
  to a too-hot plug...

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  Source:

  http://www.superhunky.com/articles/SparkPlug.php

  Tony Irani