| Choosing the right glow plug for your model will eliminate many problems and help ensure good engine run.
Glow plugs come with a heat rating, it could be number, color, or it may just tell you. The plug heat ratings range from cold to hot and everything in between. There is negative correlation between glow plug heat ratings and actual engine temperature. For example A hot plug should be used on a cool running engine to give best performance. An OS .40 running a large propeller at low rpm (10,000) and 5% nitro would probably run best with a hot to medium plug. A cold plug would be used on a hot running high performance engine as in the following example: I run a Fire Ball Super Cool plug ( one step warmer than their coldest plug) in my mvvs .40 I run 10% nitro a Macs 1140 tuned pipe a 10x6 propeller at 16,500 rpm. The engine gets up past 340 degrees and a hot plug would burn up in about 30 seconds. The Super Cool has no problem running at full power for the entire flight.
How all this works
The glow plug ignite the air fuel mixture using catalytic action. That is why glow plugs are made from expensive platinum alloy. This alloy can start glow fuel fires without becoming part of the fire. It can also start these fires without being hot, room temperature is good enough. Yes that means you could start your model without attaching the glow wire! This is because platinum atoms have cone shaped "pits" in them. These pits strongly attract atoms of hydrogen and oxygen these two atoms are forced so tightly into the pits that they combine and start combustion and become a molecule of H2O. The H2O is forced out during combustion and a new hydrogen and oxygen atom take their place and it starts all over again. As mention above none of this requires any heat to be added to the platinum. However heating the glow plug makes staring an engine MUCH easier because there are also molecules of Carbon monoxide (CO) in the pits. The (CO) will attach its self to the platinum when the wire is not heated and this reduces the effectiveness of the catalytic activity. Heating The wire drives off the (CO).
Idle bars on glow plugs can benefit some engines and not make a difference on others. The purpose of the Idle bar is to prevent raw fuel from putting out the glow burn or retarding it by shielding the element from the fuel especially during power up from prolonged idle. If your engine experiences delays or dies during power up idle bars on your plugs may help or stop the problem.