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hot, medium or cold glow plug?

Old 01-17-2006, 08:10 PM
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Default hot, medium or cold glow plug?

i have a .25 engine and would like some glow plug advise. what situation require which plugs? would a hot plug make starting easier? is a hot plug only hot when the igniter is attached? what effects would each plug have on an engine? thanks again for the advise.
Old 01-17-2006, 08:37 PM
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Default RE: hot, medium or cold glow plug?

Hotter plugs generally give better idle but they are not nessesary with correct tuning, rough guide is lower the nitro the hotter the plug larger engien cooler plug eg low nitro .12 size engine Hot plug low nitro 27 size engine medium plug see how this works..

now having said this its a guide only, you will need to try a few plugs that suit your needs but this guide will get you into the ball park ..
Old 01-18-2006, 11:46 AM
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Default RE: hot, medium or cold glow plug?

Plug choice depends strictly on the engine's compression and nitro content of the fuel. Most engines run well on fuel up to 20% with a hot/medium plug. Higher nitro like 30% requires a medium/cold plug.
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Old 01-18-2006, 12:02 PM
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Default RE: hot, medium or cold glow plug?

Well said so far.
What 'Hot', 'Medium' and 'Cold' plugs actually do is determine the ignition timing if you use a term from gas engines.

A plug that is to hot will make the engine detonate and the plug will burn out fast. You can easily see this if you got pitting on the top of the piston.
A plug that is too cold will make the engine run real bad at WOT, it sounds like it 4-stroking down the straight because it can't maintain a good glow. Many people think it's running rich and will lean out the engine to make it sound OK. It does sound OK and it will run pretty OK but it will run way too hot and the plug will burn out.

There are more things causing misfire and detonation. One important part is the distance from piston to head button at TDC. If the distance is too big the engine will detonate no matter what plug you use and it will never produce good power and run good. This is a common mistake.
A good distance for a .21 is 0.03mm. If you need to lower the compression the correct way of doing it is to mill out the head button, not adding another shim.
Old 06-22-2024, 06:19 PM
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I know this post goes back eons but it is interesting. Out of every guy I have had brought me a gas car that wouldn't start, they have always ran cold plugs. As soon as I change them over to hot plugs, everything fires up and on 16% nitro in an out of the box .21 that is all you need

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