Ok - so which one is the best glow plug. I have a lot of choices and I want to make sure that I buy the one that makes the most of my engine.

there's A3 or #8 or A5 and on and on..

Why would I choose a medium instead of a hot>? isn't the hotter the better?

Your plug choice will depend on the fuel you use( nitro %), how hot your engine is being run, wether you use a stock muffler or a tuned pipe etc. A 3 is general purpose, I doubt under non competition use , if you'll notice much difference in performance using a stock setup.

I'm not sure there is a best brand. OS, K&B, Fox, McCoy, Thunderbolt, Enya, etc. are all good. It only matters that it is the right heat. If its the wrong heat range the engine doesn't have as much power or doesn't run well, and the plug may not last long. Generally the midrange plugs of an engine manufacture match well with their engines, but may be a bit hot or cold for another. So start with the same company's plug if you can.

I believe Enya and OS use pure platinum in their glow elements where Fox and K&B use an alloy of platinum and rhodium. If the plug has pure platinum in it, the catylic reaction with the methanol will be much improved. Also it will allow the plug to last longer under normal use.

Present day convention uses the OS #8 as a standard of comparison as a medium heat range plug.

Most two stroke model airplane engines run perfectly well with this plug.

Some engines such as the H9 Evolution glow engines run better with a hotter plug such as the OS A3 plug.

The standard glow four stroke plug is the os "F"

http://osengines.com/accys/glowplugs.html See this site

Adding rhodium to the element is supposed to be an improvement. OS uses it also, it helps to keep the plug hot during idle. It also makes the element stronger. If I correctly recall, older pure platinum plugs were more likely to break from vibration.

When it comes to glow plugs, it is not a matter of saying "Brand X' is "better" than "Brand Y"

Of course, there are variations in quality between manufacturers. However, to say one brand is better than another is simplistic.

I like a lot of different plugs, and think the Novarossi range are excellent. Many have never heard of them.

O.S., by position of market dominance, are pretty much a default choice for many. They put out a quality product. To say they are the best in any given application is a matter of opinion. I don't use them personally, except for the "F" plug in O.S. and O.S. clone four strokes.

Like spark plugs .... Autolite Vs Champion; NGK Vs Denso Vs Bosch .... all are good, if used in the correct intended application. Then we get to types of spark plugs ,,, but that is an off topic discussion.

G'day You don't say what engine you have so it is not possible to say what is the right plug for you.

The heat range of plugs (hot, medium and cold) describes the way the plug affects the timing of the fuel ignition. A hot plug will cause the fuel to ignite earlier than a cold plug (ie, it advances the timing of the ignition). If you use a plug that is too hot, you risk getting pre-ignition - ie, the fuel ignites too early and may result in damage to the engine. If you use a plug that is too cold, the fuel will ignite too late and you may loose power.

You can also affect ignition timing by adding/removing nitromethane, changing the compression ratio and by adjusting the needle rich (retarded) or lean (advanced) but that is another very long story.

Most 40 size two strokes work well with the OS #8. This does not make it "the best", it just works well in most applications and it is widely available. I recently tried to run a Leo 46 with 10% nitro fuel and an A3 OS plug. The result was a disaster as it could be clearly heard pre-igniting in the mid range (a sort of crackling noise). I fitted an OS #8 and the result was much better but not perfect so I ran less nitro (5%) and the problem was fixed. It also ran happily and very economically on straight fuel with no nitromethane.

Four strokes are a different kettle of fish. They need a fairly warm plug that will retain its glow through the exhaust cycle. The OS F and other four stroke plugs are designed to do this. They often work well in some two stroke engines.

Older so called " loop scavenged" engines with baffled pistons seem to need the older "idle bar" plugs. The bar is there to try to stop large drops of fuel from quenching the plug.

Merlin glow plugs website has some good info. Iuse them almost exclusively.

I use the Fox RC Long (Medium-Hot with idle bar) on a variety of brands of two-strokes, and I like the Fox Miracle plug in my four strokes.

To give a meaningful answer we need at least some information about the engine. Size? Two stroke or four? Brand? Condition?

jess

I have found that for all my 4 strokes, the Fox Miracle Plug has always given me better service than any of the others.