What is the differants in the three glow plug?
Does the cold plug make the engine run cooler and Hot run hotter engine temp?

I asked this question a week ago. If i understand well, then the cold glow plugs are good for the summer where there are high temps, so the engine is running better. The eact thing about the hot plugs. They are good for winter. An example is the classic OS P3 and P7 glow plugs. The P3 is ultra hot and the P7 is cold. The P3 i'm using it all the time in the past. I notice though that in Summer i have a few problems because of VERY high temps here in Cyprus (this island is like desert ), so this summer i will test a P7 or either a P8 if you asking me and see the difference. They also told me that with a very hot glow plug running in Summer (high air temps), the engine might "stall".

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.

I'd also like to add two plugs from different manufacturers rated cold or hot will not be the same. A Novarossi cold plug can be as equal to one of RB's hot plugs. Always check to be sure you are running the right plug especially when using a higher percentage of nitro.

That thing about puting glow plugs of other brand on your engine is not good, because you are not sure...If the engine is Nova, i would stack with nova plugs, if OS then OS plugs etc.