Melted Spark Plug: What Can Burn Your Spark Plugs So Hard?

Without proper operation of the spark plug, your engine won't start. If you notice your spark plugs melt in the engine, this is certainly not a good sign.

In this article, I will show you the reasons for this nasty thing and also offer several solutions that you may immediately apply to avoid engine damage and other problems with your vehicle.

How do you understand that the spark plug is melting?

In the picture above you see a melted spark plug. This is the spark plug that has a changed shape of the tip or the firing unit. Such a plug is no longer capable of producing spark and it's not going to make your cylinder work properly.

If the shape of the spark plug tip is not changed, it's not called melting. There are several other types of spark plug damage like burning, buildup, overheating, etc. But I will focus on melting in this article and will offer several solutions to this exact problem.

So, now, that you know for sure that your engine has a melted spark plug or even several of them, it's time to learn more about the possible reasons for this.

Why can a spark plug melt in the engine?

Although this is not a very common occurrence in modern vehicles, I've seen some engines with melted plugs. Owners reported misfiring, loss of power, and other pretty generic engine behavior issues and I obviously had to start with checking the spark plugs, coils, etc. Fortunately, I always start with the plugs and what I saw in these engines really surprised me.

Here are the possible reasons for this problem, in my opinion:

1) Engine running too rich or too lean

When this happens, the combustion process is not as perfect as it should be. It affects the plugs because they get burned when it's too hot in the combustion chambers. It means you have more fuel than needed.

There are plenty of factors that can make your engine run lean or rich. Injectors, sensors, air supply problems, fuel pump issues, blockage in fuel tubes, etc., etc. I won't focus on this because this will take another article or two.

2) Spark plugs are not compatible with your car or just too bad

Every type of spark plug has its own heat number. This is the temperature that his exact plug can handle. And this is an important factor when buying a new set of plugs for your engine.

If you buy spark plugs with a very low heat number, it will most obviously melt, in the end. I saw this happening in one of my earlier cars with a carb engine. The engine was naturally very hot and needed a special type of plugs but I bought the cheapest set I could find (you know, student times) and found them melted after a few days.

Check the spark plug specifications when you buy them. Better get OEM spark plugs - they won't cost you much more than a set of aftermarket products.

3) Heavy misfiring in the engine

A misfire occurs when somehow the engine can't burn the fuel at the proper time and it explodes at the wrong time or place afterwards. This causes severe overheating in some parts of the engine. Sometimes, it may cause problems with the plugs, too.

Again, I will not delve into the misfiring problem because it will take an hour of reading (and three hours of writing), so you may check more about this here.

If you see the misfiring codes on the scanner and feel your engine shaking and knocking, it's time to have a look at the spark plugs - maybe they have already melted!

4) Just old and low-quality plugs

Old plugs can melt just because they are old. You need to change the spark plugs sometimes. The optimal interval depends on the engine and is often offered in the driver's manual. If you can't find it, my colleague has written an article about that - have a look.

So, old and worn-out spark plugs won't do their job perfectly. What's more, they can just lose their shape and the spark won't be formed between the tips. This will lead to misfires and will potentially affect the engine's work and even its durability.

How do you understand if the engine runs lean or rich, looking at the plugs?

It's pretty easy if you have this picture to look at and compare your plugs:

What to do if you find a melted spark plug?

Well, the things are obvious as day and night - just replace the set of spark plugs with the new one. It's important to buy the proper plugs though. I still recommend OEM parts for any engine repair or service because those have proper heat numbers, voltage specifications, and other features.

If you get cheap aftermarket spark plugs, be ready to check them regularly and make sure that they work properly. Otherwise, they may just melt or burn and stop working leaving you to deal with a lot of engine issues.

Also, if you don't have the proper tools or just don't know how to change the plugs, let professionals do that. Too tight or too loose a plug can also be the reason for problems. I've even seen a cracked head because of the overtightened spark plug.

My spark plugs keep burning and melting - what should I do?

If you replaced the spark plug kit and after a few days found one plug melted again, you may be sure there are some problems with the engine.

You will need the new spark plug set to let all cylinders work and also a good scanner that can monitor the engine parameters online. Then, you will need to find a car mechanic who can read those parameters and tell you what's wrong.

This may be the lean or rich mixture, misfiring issues, problems with fuel or air supply, issues with the quality or type of fuel, etc.

In the end, a good mechanic will easily find the reason why your plug melts instead of working happily.

Do you have experience dealing with a bad spark plug that melted? Please share it in the comments and let other readers know!