How to clean spark plugs

How to clean spark plugs

When there is a problem with the car’s spark plugs,  the most common (and advisable) thing to do is to replace them, above all to avoid greater damage to the engine. However, it is not always necessary to make the change; in some cases, it may be sufficient to clean the spark plugs properly. But to do it without causing damage, it is necessary to be clear about how the spark plugs are cleaned step by step.

Spark plugs: definition and typesHow to clean spark plugs

The spark plugs are key elements in the ignition system of a vehicle. Its function is to produce the ignition of the mixture of fuel and oxygen within each cylinder by means of a spark that can range from 12,000 to 40,000 volts. Currently, manufacturers usually recommend replacing the spark plugs between 60,000 and 90,000 kilometers, much more compared to the 10,000 – 15,000 that the spark plugs lasted in older cars.

There are two types of spark plugs:How to clean spark plugs

  • Hot plugs: they have a very long insulator tip, so the heat dissipation path is slower and thus a minimum temperature is maintained in the combustion chamber.
  • Cold spark plugs: the tip of the insulator is shorter and therefore the path of the hot air is shorter and also faster. These spark plugs facilitate the flow of heat through the electrode and its dissipation towards the cylinder head.

The use of hot or cold spark plugs depends on the degree of heat that needs to be transmitted to the cylinder head. High-performance engines require cold plugs, capable of dissipating maximum heat, while low-power engines require hot plugs to maintain the proper minimum temperature.

The spark plugs that start combustion in gasoline engines should not be confused with the glow plugs of diesel engines. The spark plugs of gasoline engines generate the spark to start combustion; while diesel engine spark plugs (glow plugs) provide support only at start-up, in low ambient temperature conditions. The purpose of this component in diesel vehicles is to bring the heat to the ignition zone to enable starting.

What happens if a spark plug fails?

When a spark plug begins to have problems, the following symptoms can be seen :

  • Difficulties in starting
  • Increased fuel consumption
  • Combustion failures (autoignition) causing a “rattle”
  • Errors in the sensors that control the injection
  • Unstable idle
  • Power losses
  • Engine running “jerk”

Not always that these symptoms exist in the car it means that the fault is in the spark plugs. However, it is one of the items that should be checked first when having a similar problem.

The most reliable way to know the status of a spark plug is by directly accessing it and removing it. Depending on how it is visually, we can get an idea of ​​what is happening in the engine:

  • Normal state. The spark plug should have a grayish-white or yellowish-gray insulator foot.
  • Sucia. We know that it is dirty when it is covered with deposits of matte black soot dust.
  • Charred. When there is a problem with the fuel mixture ratio and it is richer than normal, the spark plug has embedded black carbon.
  • Oiled. If there is any oil leakage at any gasket, it can cause the spark plug to pool with oil and not produce enough spark.
  • Worn out. The electrode has worn out and no longer generates spark (or almost).
  • With lead deposits. The spark plug is vitrified, leaving traces of a yellowish or even green color.
  • With ash. The spark plug has a thick layer of ash between the electrodes that usually comes from the different additives in the oil and fuel.

How do you clean the car spark plugs?How to clean spark plugs

In the event that there is a problem derived from the spark plugs, the most advisable and effective thing is to replace them. Manufacturers do not recommend cleaning spark plugs, as they are wearing elements and subject to replacement for maintenance.

We must also bear in mind that many of the injection systems on the market, such as the direct injection system, have a “self-cleaning” system that generates a minimum temperature of 450º in the combustion chamber, which allows that the carbon particles deposited on the tip of the insulator are burned. If even taking this into account, the spark plugs have to be cleaned, it is important to carry out the process correctly to avoid problems.

This is how to clean the car spark plugs step by step :

  • Remove the spark plug wire or ignition coil with great care.
  • Loosen the spark plug and clean the entire contour of it with pressurized air.
  • Remove the spark plug and place it on a cloth. Mark, each spark plug to assign each cylinder its own.
  • Clean the spark plug using 90º alcohol or a specific cleaner. You can also use a carb cleaner.
  • Clean the thread well with a metal brush. Cleaning the soot and carbon deposited on the spark plug threads is removed with decarbonizers or carburetor or injector cleaners. One of the best options in this regard is  LOCTITE SF 7235, a fast-acting and effective cleaner and degreaser.
  • Check the electrode distance. For reference, this should be about 0.6 or 0.7 millimeters.
  • Once clean and checked, we proceed to mount the spark plug. Make sure that it is completely dry and that the threading is smooth and without interruptions, as there is a risk of damaging the cylinder head (especially in aluminum cylinder head models).
  • Fit the spark plug and tighten it according to the torque described by the manufacturer.


Replacing or cleaning spark plugs is a complex process that must be carried out by a professional mechanic. It is important to be clear about how spark plugs are changed or cleaned correctly, as incorrect installation of these components can lead to serious problems related to optimizing engine performance and catalyst efficiency.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.