Edward,

Maybe I am wrong, but the temperature rating of a glow plug doesn't control the operating temperature of the engine, but it actually controlls the combustion event of the fuel mixture due to the temperature that the filament glows. Similar to ignition timing of a gas engine. Well actually, I kinda answered my own question, ignition timing can indirectly affect overall engine temp.

So if this is the case would a cold rated plug be like retarding the combustion event, and a hot rated plug be like advancing the combustion event?

Please clarify this for me.

BK