Seized Spark Plugs – What To Do And How To Prevent Seizing

Spark plugs are parts that regularly need to be replaced during routine servicing. Most times this can be done without any problems but sometimes they can seize. If a spark plug does seize it can be a tricky affair to get it out as it is a fragile component. Worst case scenario: a spark plug can snap if it is forced too much, in which case you will be faced with a big repair bill. Luckily, though, there are ways to reduce the risk of seized spark plugs. In this guide, we will discuss what to do if you encounter a problem with a stuck spark plug.

Why does a spark plug seize?

Spark plugs are fitted to all petrol-powered cars. They provide an electric spark to ignite the petrol and air mixture that is pushed into the engine’s cylinders. As the spark plugs are directly exposed to the extreme heat inside the engine, they can deteriorate rapidly, especially if the engine is not running as well as it should.

Carbon build-up is one of the spark plug’s biggest enemies and occurs if the engine does not run at an optimal level. Usually, direct injection engines are particularly affected. The carbon can build up around the tip of the spark plug inside the cylinder and will prevent you from removing it. Simply put, the spark plug can become seized.

Apart from that, spark plugs can also seize due to corrosion. Whilst on modern engines there is a reduced chance of this happening it can still happen. Typically, engine fluids or water from outside will be the cause. The corrosion will occur where the top parts of the plugs stick out of the engine. The fluids can slowly affect the areas in and around the spark plug threads and start corroding.

How to prevent your spark plugs from seizing

To avoid seized spark plugs it’s important to ensure the utmost care is taken when replacing them. As they are vital parts of the engine, the replacement of the spark plugs is best left to a professional who knows the ins and outs of your particular engine. Especially as there are numerous types of spark plugs that ask for different ways to remove and fit them.

A generally accepted rule, though, is to make sure the spark plugs and threads are dry of any fluids, like water, before they are put into the engine. That way there’s less risk of spark plugs seizing. If you’re not quite sure how to do it, make sure to always get help from a mechanic.

Should I put anti-seize on spark plugs?

Many spark plugs on older cars can be treated with anti-seize lubrication which can reduce the risk of a plug seizing. Having said that, on most modern cars, manufacturers such NGK, Bosch & Denso for example, advise strongly against the use of anti-seize solutions. Most of these spark plugs have been pre-treated already with anti-seize compounds to prevent this from happening. In many cases, adding anti-seize lubrication can cause more harm than good, so it’s better to check with a professional first as the torque values may need to be adjusted accordingly.

How do I remove seized or stuck spark plugs?

Removing seized spark plugs is not a very easy task if you’re not familiar with car parts so we recommend getting a professional mechanic to inspect and remove spark plugs if needed. In many cases a stuck or seized spark plug can still be removed by following a standard spark plug removal procedure with the addition of applying penetrating oil:


  • Locate the spark plugs (often you will need to remove an engine cover)
  • Remove the spark plug cap or ignition coil pack – this will give you access to the plug itself.
  • Apply penetrating oil to the spark plug seatTake the spark plug socket and thread it over the spark plug
  • Use a ratchet and tighten the spark plug – this may sound strange but it will help give the oil space to penetrate into the threads.
  • Leaving the penetrating oil to work its magic for an hour may be enough (sometimes more time may be needed)
  • Once enough time has passed slowly try to loosen the spark plug with the ratchet and socket
  • Repeat the process if the spark plug remains stuck
  • Remove the spark plug carefully once it’s fully become unseized


Always make sure you follow the manufacturer’s guidelines on removing spark plugs on your vehicle. It’s important to make sure the spark plug does not snap and break leaving bits inside the engine.

What can I do if my spark plug is completely seized?

If the stuck spark plugs cannot be loosened up and removed with the standard removal procedure then leaving the penetrating oil can help remove any buildup and corrosion that’s causing the plug to ‘stick’. The penetrating oil when left for a good amount of time will help remove all the buildup and allow you to tighten and then loosen it as needed. This process may need to be repeated several times if the spark plug is still stuck.

If a spark plug is fully seized it’s important to be very careful when replacing it. Get the help of an expert mechanic to get them out to prevent further damage. If a spark plug does snap when you try to remove it then it’s likely that pieces will have dropped into the cylinder. It’s important not to start the car until all pieces have been removed, otherwise, this could lead to significant engine damage.

What to do if my car has corroded spark plugs?

Spark plugs can also seize because of corrosion, but corroded spark plugs can also lead to reduced performance. The side of spark plugs that sit inside the engine can corrode due to the materials of the spark plug electrodes reacting in an adverse way with fuel that circulates through the engine. As that happens suboptimal spark plug gaps will develop, which subsequently will lead to poor engine performance.

How can I prevent carbon build-up on spark plugs?

Some spark plugs may also suffer from carbon build-up as noted earlier. Whilst there will always be some carbon building up as you run the engine there are ways in which you can reduce this. If you do a lot of stop-and-go driving it can’t harm to rev the engine a little more than usual to blow some of the nasty carbon stuff out of the engine. Also, it’s helpful to make sure you replace oil and filters regularly and to use good quality petrol.

Is it ok to spray WD-40 on seized spark plugs?

In general, we do not recommend WD-40 to loosen spark plugs. While WD-40 is a good general-purpose lubricant, it is not designed to be used on spark plugs.

While in most cases, it may not cause any harm at all, it is possible that WD-40 on spark plugs can cause problems such as fouling the spark plug, which can lead to misfiring, reduced performance, and potentially cause damage to the engine. Having said that, WD-40 is a good way to keep moisture away – so it’s a good way to prevent seizing.

If the spark plug is really stuck, you can try using a penetrating oil designed for use on spark plugs, but always follow the manufacturer’s instructions and be careful not to get the oil on any other parts of the engine.

Why do spark plugs need replacing sometimes?

Spark plugs need to run at a hot enough temperature to burn off any carbon and ash deposits that build up on the plug as the engine runs. If the plugs cannot run at the right temperature, though, deposits will build up. It will decrease the engine’s performance and lead to higher fuel consumption and misfires.

On the other hand, spark plugs shouldn’t be too hot either. This will cause the fuel to ignite before the plug can actually spark and ignite the fuel. This eventually can lead to the detonation of the plug, which may damage the engine beyond repair.

When should I replace the spark plugs?

If your car is not starting well or acceleration is sluggish then it is usually a sign there is something wrong with your plugs. Especially if your fuel consumption is higher than normal as well. At that point, it’s probably a good point to replace your spark plugs. Replacing them as soon as possible will probably save you quite a bit of petrol money in the long run.

Remember, sometimes it may just be the one that is affected. But it’s more likely all of the plugs will wear out at the same time. In most cases, it is advisable to replace all your spark plugs in one go anyway. This is to ensure all the plugs have the same strength enabling the engine to run smoothly.

If you’re not sure when to change the spark plugs then it’s worth getting help from a mechanic. They can inspect the plugs and determine if they need replacing. Moreover, they will also be able to pinpoint if there are any other issues in the engine. Like engine knock or detonation.

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