Glow Plug temps - please explain

Hot plugs are generally used for low nitro applications, 0-15%. They're also used in high percentage castor fuels. This is a common heat range for control line useage. The R/c crowd would use this plug in addition especially on older baffle piston engines which required low idle and peppy transitions. If the temp was cooler, the plug would drown out so many hot plugs have a additional idle bar which supposedly shields the plugs element from an abundance of fuel getting thrown at it.  Medium temp range would be used for 10%-25% nitro fuels and this is a very common plug for modern r/c engines. However, these can be substituted for hot plugs if idle transition is cooling off the plug. Medium plugs would have a better lifespan due to the element being slightly heavier over the hot versions. Cold plugs are used for low compression high nitro fuels of 25% on up. Engine type and useage have a very large deciding factor as to what type of plug is required. They also have the heaviest element and take a bit more to light them up.

      In general, experimentation is important but your nitro content is a very large part of the equation. Hot is for low nitro and cold is for high. Cox engines in general work superior on high nitro fuels. This assists in maintaining cylinder heat and needling of the engine. Ken