Anyone out there know which of the following hot plugs is the hotest and which is the coolest with respect to each other?
OS F Plug
Fox Miracle Plug
McCoy 4C Plug

My experiance is that the Miricle Plug is a shade cooler than the OS, don't know about McCoy. If you are looking for a cooler plug that will run better on high nitro, 25% and above, try the K&B 4-Cycle plug.

General Glow Plug Information - Consolidated

By James McCarty, Brian Cooper, Brian Gardner, and others
Including www.flightlines.com


OS Glow Plug Information

No. 8 Hot Recommended for most current O.S. (and other) 2-stroke engines

Type F Mildly Hot Special long-reach plug recommended exclusively for O.S (and other) 4-stroke engines

Type RE Hot Special long-reach plug designed exclusively for O.S. Wankel rotary engine

A5 Cold Recommended for most current O.S. (and many other) 2-stroke engines particularly for 1/10th & 1/8th scale off-road car engines

A3 Hot Dependable O.S. quality makes A3 the most durable and longest-lasting glow plug available at an economical price

R5 Very Cold Recommended for high-nitro fuel and high r.p.m. engines, particularly 1/8th track racing car engines


ENYA Glow Plug Information

# 3 Hot All Enya engines such as TV & four cycle engines

# 4 Mildly hot All Enya engines, especially those used with 10%or greater nitromethane fuel

# 5 Medium All Enya engines, especially the .40CX, .45CX and high nitro methane fuel/

# 6 Cold High compression engines and high niro methane fuel used in racing.



Fox Glow Plug Information

All 1. 5 Volt Plugs are Dry Cell or Ni-Cad All 2 Volt Plugs are Lead Acid Battery

Standard Short Hot 1.5 Volt, Standard Short Hot 2 Volt

Standard Long Hot 1.5 Volt, Standard Long Hot 2 Volt

Gold STD Long Plug Hot 1.5 Volt, RC Short Mildly Hot 2 Volt

Gold RC Long Hot 1.5 Volt, RC Long Mildly Hot 2 Volt

RC Short Mildly Hot 1.5 Volt

RC Long Mildly Hot 1.5 Volt

Miracle Plug Hot 1.5 Volt

Pro 8 Short Cold 1.5 Volt

Pro 8 Long Cold 1.5 Volt



McCoy Glow Plugs

W/OS Equivalent

MC-8 Cold A5, R5

MC-9 Medium Hot #8

MC-50 Hot IDLE BAR – LONG

MC-55 Medium Hot A3, #8

MC-59 Very Cold

STD ROSSI GLOW PLUGS BI-TURBO GLOW PLUGS (without idle bar) (conical w/o washer)

Rossi Glow Plugs (cold for pattern type work / high nitro fuels, hot for sport / low nitro flying)

R1 Extra hot 0.8 to 2cc RB4 Hot

R2 Hot from 2 to 3.5cc RB5 Medium

R3 Medium from 3.5 to 6cc RB6 Cold

R4 Cold from 6 to 10cc RB7 Extra cold

R5 X-cold for nitro fuel & R/C RB8 Super cold

R6 Cold nitro 10 to 13cc

R7 Cold for nitro 13 to 15cc

R8 Cold for nitro 15 to 30cc GLOW HEAD FOR R15

G1 Hot

R/C GLOW PLUGS

G2 Medium (with idle bar)

G3 Cold nitro 15 to 30%

RC Hot for 2.5 to 6cc

G4 X-cold nitro 30 to 50%

RC Cold for 6 to 15cc

G5 Cold nitro 50% or more



Glow Plug Usage Tips

Your glow plug temperature range is too cold when:

· The engine power is weak or has weakened from previous levels.

· The engine slows down considerably or stops after removing the glow plug battery, despite correct adjustment of the needle valve. For example (Enya), if a # 4 plug gives you these problems in your engine, switch to a # 3 plug instead.



Your glow plug temperature range is too hot when:

· The engine suffers from pre ignition and loss of power.

· The overall engine running is rough

· The glow plug filament is broken or collapses frequently.

These are several cures to these problems. We suggest using a fuel with less nitro methane content, using a larger size propeller or using a colder plug than the one currently in use. For example if an Enya # 3 plug gives you these problems in your engines, switch to a # 4 plug.



Model glow plug engines are extremely dependent upon the type and quality of the glow plug used. Enya glow plugs use a platinum alloy coil, which uses a thick diameter wire for long life. The thicker wire coil also eliminates the need for an "idle bar" as found on other brands of glow plugs; idle bars tend to reduce top speed slightly, to achieve a more stable idle speed. Enya's glow plug design insures both good top end speed and stable idle speed.

Enya glow plugs also have a thicker battery contact at the tip of the plug for greater heat dissipation and better electrical contact. Altech Marketing presently stocks glow plug battery cords specifically for Enya glow plugs, which are standard equipment with Enya four-cycle engines. Other glow plug cords usable with Enya glow plugs are available from several other manufacturers.

HOT GLOW PLUGS (for low nitro and FAI fuels)
Enya: # 3
Fox: Miracle, Standard, and R/C Long (2V)
Fireball: Hot (1.2-3.0V), and S-20 R/C Long
Fire Power: F 6 (warm), and F 7 (hot)
K&B: 1 L
McCoy: MC 55 R/C Long, MC 59, and MC 14 (very hot)
O.S. Engines: # 0, # 1, # 5
Rossi: R 1 (extra hot), and R 2
Sonic Tronics: Glowdevil # 300
Thunderbolt: R/C Long

MEDIUM GLOW PLUGS (for 10%-15% nitro fuels)
Enya: # 4 (medium hot), and # 5 (medium cold)
Fireball: Standard (1.2-2.0V)
Fire Power: F 5 (medium), and F 6 (warm)
Fox: R/C Long (1.2-1.5V), and Gold
Hanger 9: Sport Long
McCoy: MC 50, and MC 8
O.S. Engines: # A 3, # 8, # 9, # 7 (with idle bar)
Rossi: Medium, and R-3
Sonic Tronics: Glowdevil Standard
Tower Hobbies: Tower Power Performance plug, and Reg. (w/bar)

COLD GLOW PLUGS (for high nitro; 25% +)
Enya: #6 (cold)
Fireball: Cool (1.2-1.5V)
Fire Power: F 2 (extra cold), F 3 (cold), and F 4 (cool)
Fox: R/C (1.2V), and # 8
K&B Long & Short high performance nitro plug
O.S. Engines: R-5
Rossi: R 4 (cold), and R 5 (extra cold)

FOUR-STROKE GLOW PLUGS (hot)
Fox: Miracle plug (often used in 2C’s W/low nitro)
McCoy: MC 14 (very hot, often used in inverted 4C’s)
O.S. Engines: Type F
Sonic Tronics: Glowdevil ST 301/302

IDLE BARS

Idle bar glow plugs came about because some engines were having trouble transitioning from idle to high speed. When the throttle was opened from idle, the incoming air and raw fuel would strike the glow plug’s heated coil, cooling it to the point where it would no longer support the combustion process, so the engine would die. To help prevent this, the idle bar was added to the glow plug to serve as a physical shield, helping to keep the coil from cooling off too quickly.

A glow plug with an idle bar will not increase peak RPM (it may even reduce it in some cases), but it may improve the idle with some engines, since it simply helps to keep the plug hot enough to light the fuel. If your having transition problems, you might want to try using a glow plug with an idle bar. Some modelers use idle bar plugs in the winter only, since the glow plug tends to loose heat faster in the colder environment.

Naturally, all of this assumes that you have the low speed mixture adjusted correctly to begin with.

HOT PLUGS

So what is a ‘hot’ plug, and how does it differ from a ‘cold’ plug? Naturally, a hot plug will heat up faster and stay hotter, but that’s not the whole story. When discussing this aspect of glow plugs, another very important aspect must be considered, the amount methanol in the fuel. The more methanol we’re using (i.e., less oil and less nitro), the hotter the plug we should use. Conversely, the more nitro and/or oil we use, the less methanol we’re using, so we use a cool(er) plug. An extreme example would be when using a very high nitro content fuel in a very high RPM engine (a typical ducted fan engine, for example). Here we’d use a very cold plug. For most sport pilots using fuel with just 5-15% nitro, however, a hotter plug would probably do well.

Probably? Yes, trial and error is often the best (and sometimes ‘only’) way to determine the right glow plug for your application. Most 4C engines need either high nitro or hot plugs to run at their best, since they have combustion strokes only half as often as 2C engines.

RULES OF THUMB TO LIVE BY

A. Use a hot plug with low nitro (less than 24%), and a cold plug with high nitro (more than 25%).

B. If you remove the glow starter from you idling engine, and notice an immediate drop in RPM, you may need a hotter plug or more nitro.

C. If your engine has a tendency to backfire a lot, you may be using a glow plug that’s too hot, or you may need fuel with less nitro.

D. Most hot plugs can take up to 2.0 volts starting power without burning up, while most cold plugs prefer 1.2 to 1.5 volts starting power.

w8ye,

Thanks!!!

That was just the info I'd been looking for for a while...

Thanks again!

I don't get the more methanol the hoter the plug. More like the more nitro the colder the plug. If you increase the oil and reduce the methanol, keeping nitro the same, you still need a hotter plug, not colder. It's all because nitro ignites at a lower temperature than methanol.

I know a guy who has a PhD in Chemistry from Cornell, and he has confirmed for me that niromethane has a much higher point of ignition than methanol. That is a common misconception. One time, that friend proved it by putting a burning match out in a soda cap full of pure 99.95% lab-grade nitromethane. Nitromethane does make more power, but not because it is a fuel. It is an oxidizer. It supplies more oxygen to the fuel/air mixture. The glow plug ignites the methanol, which heats the nitro and releases more oxygen, which causes more methanol to burn faster.... you get the idea. Its just like nitrous oxide. Contrary to what they showed on Fast and the Furious, nitrous will not accumulate and explode like propane. (which is what they used in that stunt) Now if the gas tank was rupture as well, and a spark was made......then you'd be talking. Anyway, just trying to clear things up.

W8ye...where do the K&B plugs fit into this list? In some older OS engines I've been running the 4520 plugs. Seems to help and the pricing is good. Tom

K&B plugs

R/C Long Reach - Idle Bar (4520)
R/C Short Reach - Idle Bar (4530)
HP high performance Long Reach (7300)
HD heavy duty Long Reach (7310)
1L Long Reach (7311)
1S Short Reach (7321)

NEW 4C Four Stroke (4444

I'm sorry but the only one I'm familiar with is the 1L and it is considered a hot one. I don't have any individual info on the K&B's.

Jim

W8ye..Thanks, I didn't know K&B made so many plugs. As I said, I'm only familiar with the 4520's. Thanks, Tom

To bad Champion doesn't still make plugs. Very good in their day. I still have a few as collector items.

This has been a very good discussion on hot vs cold plugs but can anyone enlighten me on short vs. long plugs? Is there a general rule such as long for 4-stroke and short for 2-stroke engines? Thanks. Jack

This is a very good thread. I plan to cut paste most and give as hand outs at our club meeting. In the "Rule of Thumb" I saw low nitro was considered less than 24% and high 25% or greater. Is this right? I guess I considered low nitro @ 5% or less, medium at 6% to 14%, and 15% or greater as high. I got this on RCO about 5 yrs ago in a thread G. Aldrich had on fuels although he wasn't the one who proposed these percentages.

As a general rule, .15 and smaller engines use short plugs and the larger engines use long plugs. There are 4 stroke plugs that are used in 4 stroke engines but some big engines like the 'MOKI' seem to like a four stroke plug even though they are two stroke.

The OS and Tower Power long plugs are medium in length. They are too short to be long and too long to be short but they seem to work fine where ever you use them.

There's a new style torpedo plug that has a conical shape on the end. I'm thinking they first came out in Rossi engines but I noticed that OS makes them now. I don't know what other engines use the torpedo?

Enjoy,

Jim

The glow plug in a glow engine IS NOT kept hot by the combustion that takes place in the cylinder.

It is kept hot by a catalytic reaction of the Platinum in the glow element, on the methanol in the fuel.
If you put a drop of methanol on a glow plug, it will not start to glow by itself. But after you preheat the glow plug with a battery and the engine is started, the heat in the combustion chamber makes the catalytic reaction much more intense, enough to keep the plug glowing red, or even orange.

There are the thickness of the glow element in the plug, its shape, the plug's internal housing shape, Etc., that are variables, which contribute to determine the heat range. But the most dominant of all is the Platinum alloy used.

Plug manufacturers add Iridium and Rhodium to the Platinum in the alloy (I don't know which makes the plug hotter and which colder).

Gasoline has a higher burning temperature than methanol and it has much less of a cooling effect on the engine. But if you try to run a glow engine on gasoline, it will shut down the second you disconnect the plug lead/glow starter. This, because platinum has no catalytic reaction with gasoline.

Sincerely,

The glow plug in a glow engine IS NOT kept hot by the combustion that takes place in the cylinder.

Not true the first glow plugs did not have platinum in their alloy. The catalytic reaction inhances the performance, it is not the primary reaction.

If you put a drop of methanol on a glow plug, it will not start to glow by itself.

There has to be a reaction in the first place for the catalytic reaction to work, i.e. the fuel has to be burning.

This, because platinum has no catalytic reaction with gasoline.

Not true, the catalytic converters in our automobiles have the same reactions going on and they work very well with gasoline.

In fact they work best with nitro because nitrogen sticks to the catalytic element exposing the carbon and hydrogen elements to make a quicker bond with oxygen. Of course without nitro they work with the nitrogen in the air.

See the SmartPlug thread. Also do a search on catalytic converters and how they work.

Platinum is also the catalyst in an automobile catalytic converter. But there it converts Carbon Monoxide and Hydrocarbons into harmless water and Carbon Dioxide.
It does not break down methanol, as there isn't any. The CC also needs to be very hot to function correctly and combustion does supply the needed heat.

The catalytic reaction is actually enhancing the combustion that is already taking place in our exhaust system. By attracting the nitrogen and other noncombustible atoms it better exposes the carbon and hydrogen to the oxygen. It does not need heat so much as it needs to wait for our car to warm up enough that the oxidation becomes more prevalent. The enhancement of the oxidation process makes the catalytic converter hotter than the rest of the exhaust system. With glow plugs it is the heat we are after. The combustion is enhanced at the surface of the plug which makes the plug hotter. The fact is that a catalytic reaction cannot start the reaction. Exposing the combustable atoms to the oxygen itself does not get the process going.

You are assuming the following steps occur;

The engine compresses the fuel and air mixture.
This adds heat to the mixture.
The heat causes a catalytic reaction with the platinum element which ignites the mixture.

However this cannot happen because a catalytic reaction cannot initiate the reaction.

The actual process is:

The engine compresses the fuel and air mixture.
This adds heat to the mixture.
The added heat plus the red hot surface of the glow plug initiates a reaction at the surface of the plug.
A catalytic reaction occurs at the surface of the plug which causes two things.
1. The glow element gets hotter which helps it to retain more heat for the next cycle.
2. The combustion gets a better start because of the improved combustion near the plug. This improves flame front just as a hotter spark does in a gas engine.

Don't assume that just because our glow plugs don't work with gasoline that glow plugs will not ignite gasoline. Our glow plugs were not designed for gas and may be way too cold or hot to use with gasoline. Even if it did work it may cause severe detonation. If yo read the SmartPlug thread you will see that they are using a high tech glow plug with gasoline.

Sport_pilot,

Your last input was right in general.

I must add; I had an HB.40PDP engine that after being stopped, if you did not wait too long and it was still hot, would start spontaneously if you just flipped the prop, without connecting power to the plug. The catalytic reaction is that strong.

The catalytic reaction of the Platinum catalyst, on the gasoline substrate, in a model engine type glow plug, is too weak to keep it hot enough for ignition, despite the higher flammability of gasoline.

The SmartPlug does use a catalytic ignition process, but it is different from what exists in an OS No.8, although it is not explained in the thread, or the web site.

Sincerely,

Dar, if what you say about the reaction keeping the plug lit was true then a rich running engine wouild never drown a glow plug, it would just get hotter and and keep the engine right on running.

Hobbsy,

It IS catalytic reaction that is keeping the flame going.
If you spill a whole bucket of gasoline on a burning candle, it would dowse the flame.

If you disconnect the glow plug lead from a rich running engine, it would slow down. Make it richer still and it will shut down.
I already wrote that if you just wet a glow plug in raw methanol, it would not start glowing spontaneously, didn't I?

The initial heat is needed to start the catalytic reaction. As long as you don't drown it with cold methanol, or deprive it completely of the same, it will go on.

Sincerely,

and after all this they cost only 2/3$ , interesting!

I learned that (I didn't see this mentioned above) if you have an engine with too much compression or gets too hot in a cowl use a colder plug.
Me, personally, I use K&B 1Ls for just about every two stroke I have. Those that run hot or have a bit too much compression I use the K&B HPs.
Four strokes get the expensive O.S. Type F.

Yes, platinum reacts with methanol. Without the reation our glow plugs wouldn't work. It is both the catalytic reation AND the remaining heat within the plug due to combustion that make them work. What's the problem?

Start an engine and immediately remove the glow starter. It will probably quit and not just because there is too much unburnt fuel in the case.

The catalytic reaction between the platinum plug element and the methanol most definitely is the important factor, otherwise the glow plug manufacturers would be using something a LOT less expensive.

Next time you have to replace a glow plug because the engine runs poorly (or not at all) when you remove the battery, look at the element under a magnifying glass and compare it to a new plug element. If you look closely you will see that the plug element is probably "frosted" or coated with something that causes it to appear whitish compared to the new plug element. What's happened is that the plug element has been coated with something that has "cooked" onto the coil (silicones in some oils used as after-run oil are bad to do this, as well as anti-foaming agents some folks add to their fuel). This coating dramatically reduces or completely blocks the catalytic process from occuring rendering the plug useless even though it's still electrically sound.

Good point Curt. 'When glow plugs go bad."

I found a research paper on the web last night where they were experimenting with various heated catalytic elements. I think the fuel was methane gas but I know it wasn't methanol. Anyway the best catalytic elements ignited the gas at a lower temperature than it's normal ignition temperature. I think the best element ignited it at 360 degrees C. So I guess this is why some have reported engines igniting without a glow driver. A hot day, warm engine, and high compression could possibly heat the fuel mixture to that temperature. Keep in mind the catalytic element did not initiate the reaction, it just oriented the atoms so that combustion is more easily accomplished.