Since most forums are open source of information and there was no disclaimer saying I could not repost this information I figured I would share a little of my research
So I admit I am a little wrong in my assesment to run hotter plugs in the winter but as these guys say it will idle better and stay running longer at Idle because in colder temps you will need to run a richer mix.
The words below are not mine and borrowed from sitelink to a Forum down in South Africa then repost what there suggestion are on Glow Plugs
I hope this additonal information helps you guys out
I will provide a link to a Forum down in South Africa then repost what their moderatorssuggestions are on Glow Plugs
But a rule of thumb you can all follow is the following
less nitro = Hotter Plug
More Nitro = Cooler Plug
So lets look at the Rossi range of plugs, because they are easy to follow... with low nitro you would use a # 5 plug say 15% 15 to 20% use a #6 (slightly warmer) 25 to 30 % nitro use a #7.. Besides the cooler plug retarding the ignition slightly it also has another purpose. Cooler plugs generally have a thicker element; the thicker element is also more resilient to higher impact explosions made by higher nitro. But in my opinion I always like to use a med to hot plug no matter what, cool plugs just don’t work for me... some people do like them but i dont.
Advantages of warmer plugs are they idle better and are harder to flame out.
Disadvantage they are a little more fragile...
Does the heat range of the plug make the engine run at a different temp? No it makes no difference except for one thing, a hotter plug will in most cases let an engine run harder therefore running hotter. It would seem the plug makes the engine hotter but its not, its like running a body without ventilation, it makes the engine run hotter but the body causes the symptom because it has changed a determining parameter... (I hope that makes sense
Ok now long body and short body plugs.
Simple really a short body plug increases geometric dome size reducing compression. A long body does the opposite; it reduces geometric dome size increasing compression.
So long body = better power = hotter engine
Short body = Less performance = cooler engine
Ahaaaa! You said the plug makes no difference to the temps! Well the heat range of the plug doesn’t but the physicality of its dimensions does. Its + or - a determining factor of how the engine runs. But all this is untrue really...... WHAT? ....
What’s really happening is a higher geometric compression will increase heat conductivity to the head button and release heat transfer via the heat sink more efficiently thus giving the impression the engine is running hotter for all you temp gun freaks out there... The reverse is true when you decrease geometric compression. This also applies to reducing head clearance; the engine will transfer more to the head as opposed to through the side walls and pipe. Remember the head button is aluminium and ally likes to absorb heat and dissipate it usually toward a cooler direction, towards a cooling head...
Glowplugs are common to all "glow" engines and are used with methanol-based fuels. The glow plug itself is made up of a steel "plug" with a platinum wound wire element that when inserted into the head of the engine forms the uppermost portion of the combustion chamber. In operation, there is a catalytic reaction between the alcohol and the platinum element that, when combined with the right compression, causes the alcohol to burn. We initially attached a 0.5-1.2V battery to the glow plug to cause it to glow, and remove this battery once the engine is running and the element continues to glow through the catalytic reaction.
You will hear of glow plugs being referred to as "hot" or "cold" plugs. Both of these terms refer to the heat range of a glow plug, and it is easiest to notice the difference at an idle. In general, the "hotter" the plug, the richer the mixture can be at idle and the engine will continue to operate. The "colder" the plug, the mixture will need to be leaned out in order to operate properly.
Assessing the Condition of Your Glow Plug
The glow plugs on the market today are designed to provide good service to the user and may last a long time or a short time, all dependent upon the way you choose to operate your engine.
Physical indications that you might need to change the glow plug are:
a. Twisted or mangled glow plug element. (This is usually caused by too high a compression ratio.)
b. Small "bumps" are attached to the glow plug element (This will generally be most noticeable during the break-in process. These are actually tiny pieces of aluminum that have attached to the element and these will severely hinder the operation of the glow plug.)
c. The glow plug element is no longer shiny but is dull, almost a white powder color. (This just comes with age and is a by product of the catalytic reaction. The shinier the wire, the better the catalytic reaction can be.)
Operating indications that you need to change your glow plug are:
a. The glow element will not light with a charged glow igniter. (This indicates that there is a physical short or breakage in the element wire itself)
b. Glow plug lights but the engine will not stay running once the battery is disconnected. (This is usually an indication if the microscopic particles we discussed earlier)
c. Glow plug lights, engine runs but there is a perceptible loss of rpm at full throttle when the battery is disconnected. (This is a typical indication that the white powder residue is building to the point that the catalytic reaction of the glow plug is no longer anywhere close to being optimum.)
GLOWPLUG #1 = The engine was set too lean, this glowplug is overheated you can see the spiral is going inwards and the worst case scenario is that the spiral brakes and drops in your engine!!
GLOWPLUG #2 = This glowplug is from a good working engine with a perfect fuel micture.
GLOWPLUG #3 = The engine was set too rich, the spiral is black due to the excessive fuel in the chamber, this engine will start very hard and does not run smooth.
GLOWPLUG #4 = This one is old and used alot, time for a new one, the extra thing you can see is that the spiral is rather white, this means that the setup of the engine fuel mixture was ok
A very important thing for a long lasting engine: regulary check your glowplug and the engine temperature!