Motor timing is adjusted by the Glow temps. Humidity plays just as a big a deal as temp. Hot plugs could cause the fuel to egnite early where the cooler plugs delay the fireing. Check the engine and try differnent plugs at the same tunning, you can really hear the difference. But the plug does not affect the engine temp just when the fuel fires. If it is hot you want a cooler temp plug, but if there is a lot of humidity you will need a hotter plug. If it is cool you need a hotter plug. This is also how you tune the engine before each race. Cooler temps you need to richen the mix, for higher Nitro it needs to run rich. If it is hot you need to lean the mix and if it is humid you need to lean the mix. It has to do with the amount of O2 in the air. Cool air has a higher dinsity and carries more O2. Hotter air is low on 02. Humitity means that there is less O2 because of the H2O is taking up some of the space so you need to lean the mixture as well. The fuel mix will change the temp of the engine not the plug.