How to Read your Rc Glow Plug. Do you have your Nitro Engine Tuned Correctly?

Posted: May 6, 2011 in glow plugs, Julian's RC Tips
Tags: , ,

How to Read your Rc Glow Plug. Do you have your Nitro Engine Tuned Correctly?.

This is one of the best glow plug articles I’ve found online. Hope it serves you well!

How to Read your Rc Glow Plug.

Do you have your Nitro Engine Tuned Correctly?

What exactly is our glow plug telling us.

So you are wondering if you have rc nitro engine tuned correctly.

You check your temperature on a regular basis, but you are still not sure.

You can examine your glow plug to get a very good idea. Examining the glow plug is a peek inside the combustion chamber.

But let’s get the big picture and take the head button off, while leaving the glow plug installed in the head.

What we are going to see by looking at the head button and the glow plug is the entire combustion process.

This is going to show use just what is left after the burn process.

By looking at the entire combustion chamber we can analyze what was happening during the burn.

Let us explore a few different tuning examples below.
Rc glow plug picture

Pictured above is an example of a Rich Setting.

This is what your glow plug and head would look like after break-in.

The head and glow plug will be very wet with oil. Every thing still looks new.

No discoloring of the head, plug body or plug coil. If this is the look just after break-in that is great.

But, if this is post break-in then you are going to need to start leaning the engine out, to reach correct combustion.

If you run in a too rich state for a long period of time, oil will build up in the crank case and cause the front bearing seal to leak.

Rc glow plug picture

The previous example is of a Too Lean or Detonation Condition.

Upon examining your head and glow plug you find or feel little or no oil residue.

The glow plug body is blued. The coil wire has broken away from the plug body.

You see that the combustion chamber is silver to slightly tan. Plus the head and glow plug are extremely pitted.

Your nitro engine is running too lean.

The pitting is caused by detonation.

Detonation is when the fuel air mixture pre-ignites in many different areas of the combustion chamber at one time.

The top of the piston will show the same kind of damage. If you see this kind damage you need to richen up your engine.

You may need to also shim your head. Increasing your head clearance will lower compression and lessen the possibility of detonation.

Rc glow plug picture

In the above example you can see why it is important to look at the head and glow plug together.

This example shows a Borderline Lean with a Good Glow Plug.

By just looking at the glow plug you would think that your nitro engine tuning was correct.

But, looking at the head you see that there is some pitting occurring.

With seeing this damage you know that your rc nitro engine is tuned too lean and you need richen your carberator setting some.

Rc glow plug picture

If you are a serious racer, this is how your glow plug and head should look.

Above is an example of a Perfectly Tuned Race Engine.

As you can see on this head and glow plug there is an even coloring across the combustion chamber and glow plug.

If you do a lot of racing this is the coloring you are looking for, that light brown to deep golden color.

This shows you that you are getting the most out of your engine. Your nitro engine tuning is producing maximum power and you have the perfect tune on your engine.

The only thing that you will need to do is keep your eye on is atmospheric conditions, temperature and humidity.

As these conditions change, so is the tune on your engine. So, always be aware of the weather conditions to help with your nitro engine tuning.

Rc glow plug picture

The previous example is of a nitro engine that has a Safe Every Day Tune.

If your head and glow plug look likes this example and you are a novice racer or a basher, this is great.

You have done a great job of tuning your nitro engine.

The combustion chamber shows a little color, gold to tan.

Plus, the chamber and plug are still quite wet with oil residue.

The glow plug also shows some color on the body of the plug, grey to tan.

The coil wire will be shiny, silver and still have a new look to it.

The only place the coil wire should show some color is where it contacts the outer body of the plug.

At this point the coil wire should be slightly black.

This head and glow plug show an engine that is running great, a little on the rich side.

This type of tune on your nitro engine is very good to get the maximium life out of your engine.

Plus, this tune would be great for bashing and even for most of us weekend racers.

Taking the Mystery out of the Glow Plug

Rc glow plug picture

In this example we see a glow plug that has been run at a Lean Setting and has got very Hot.

On inspection we see that the outer body has turned black.

The coil wire has a white dusty appearance.

Plus, the coil wire has small breaks in the electrode wire.

All of this is due to the very extreme heat of running lean.

This glow plug is near failure, the coil wire is close to breaking free of the body.

If the tip of the coil wire was to break off it could travel down into the engine causing severe damage to piston, bearings and head button.

But, most times when the coil wire does break off it will just go out an exhaust port causing no damage.

This will not always happen, if the coils wire stays inside the engine it will destory many internal components.


I hope this has given you a little insight about nitro engine tuning. The glow plug what makes our nitro engines run.

Besides just looking at our glow plugs, it is important to remove the head button and look inside our engines on a regular basis.

Doing so is going to give us the whole picture of what is going on, not just a little peek the glow plug gives.

Yes, checking our glow plugs often is very important and gives a good look at what is going on inside our engines.

But, just remember that this is not the big picture.

Take a few minutes to clean your engine thoroughly, remove the head button and take a close look at what is going on inside.

  1. jeff says:

    Ibought my self and my son two madfire buggies and we r beinners and i mean i havent said glow plug since 1968 when i flew a cox plane on a cord. very general how do i charge the charger that ignites the glow plug. i have the iten that goes to the wall outlet and the other end shoukld go in the igniter but it isnt charging. help. jeff

    • Yes it charges, but very slowly. Your best bet is get one of those 150-200 watt multi-chargers on for under $40. it’s got a peak-charging function, plus you’re able to charge your ignitors at a higher current. The one that comes with the ignitor charges at 0.2 Amps, which half of it is lost in electrical resistance. I charge mine at 1.4A. While this does affect the lifespan, it saves alot of time, and it also increases the performance.

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