Originally Posted by
1QwkSport2.5r
To go one further; there are two functions of the heat range of the plug. How much heat the body retains, and how “hot” the wire is. Some manufacturers make plugs such that there are hot body and cold body plugs, and also hot, medium, and cold elements. You could get a cold body hot element plug, hot body medium element (my preference), etc. Its just more way to fine tune the engine.
Generally, the glow plug heat range is chosen based on the methanol content. The higher the methanol (lower nitro) content, the hotter the plug needed. Methanol itself burns pretty slow, so more heat is needed.
Do you have any info on how to differentiate between hot body and hot wire? Or is that just a matter of "this brand such and that brand so"? Because I cannot remember having seen that info listed by any of the name brands to be honest.
Also: to a certain extent, and this is more an "aero-engine" thing
AFAIK, engine size (displacement) also does play a role according to some plug manufacturers, larger engines can do with colder plugs. At least, that is what Rossi says on their plug blister packaging. But that is more a rule of thumb.