How to Change Spark Plugs and Glow Plugs


    – Two types of car spark plugs

    – Gasoline engine: spark plugs

    – Diesel engine: glow plugs

    – Where to go to change the spark plugs?

    – How to replace your car’s spark plugs?

    – Price of car spark plugs

Different maintenance for gasoline and diesel

Like the alternator, the car battery, and the car’s light bulbs, the car’s spark plugs are part of the electrical system and essential for starting the vehicle.

A car spark plug is used to start the car: its role is to ignite the air-fuel mixture, thus allowing the engine’s combustion to start.

Two types of car spark plugs


Gasoline and diesel vehicles do not use identical spark plugs since their function differs depending on the engine:

  • Gasoline cars start with spark plugs.
  • Diesel vehicles, on the other hand, are equipped with glow plugs.

Gasoline engine: Spark plugs

Spark plugs for cars

Spark plugs provide the necessary spark for the combustion of the air/fuel mixture in the engine’s combustion chamber.

However, these spark plugs are subjected to great stress, withstand extreme temperatures, and are worn out after many years and miles.

Replacement frequency

The service life of spark plugs is significantly shorter than that of glow plugs:

  • 10,000 to 30,000 km ;
  • except for models with a silver or platinum centre electrode, which can last up to 50,000 km.

Symptoms of wear

Many symptoms can alert you to this:

  • Dirty spark plugs (very thick, powdery, black deposits);
  • oily spark plugs (the spark plug tip is completely covered with a black oily film, possibly due to excess oil in the combustion chamber)
  • melting of the electrode ;
  • worn electrode ;
  • breakage of the insulator;
  • loss of combustion of the engine due to insufficient tightening;
  • scale deposits.

Causes of wear and tear of these car spark plugs

All these symptoms can be linked to a:

  • lousy adjustment of the engine;
  • bad fuel;
  • wrong additive (too corrosive);
  • bad choice of spark plugs;
  • bad assembly.

You must identify the causes to carry out quality maintenance.

Diesel engine: glow plugs

In a diesel engine, there is no ignition and, therefore, no glow plugs. The engine is started immediately after the combustion chamber has been preheated. The glow plugs (one per cylinder) do not create a spark but glow for a few seconds to preheat the combustion chamber.

On some modern vehicles, combustion chamber preheating continues for a few seconds after starting the engine to bring it to its ideal operating temperature more quickly.

Replacement frequency

Glow plugs only work during start-up, so they last much longer than ignition plugs. In general, glow plugs should be replaced after 40,000 km, in some cases up to 80,000 km.

Wear symptoms

Wear’s symptoms are mainly related to the glow plug’s tip, which may be damaged, broken, melted or sifted. Also, the white smoke that may appear at start-up is an indication of poor diesel combustion.

Who should I contact to change the spark or glow plugs?

Changing a spark plug is the same as changing a glow plug; it is easy. However, you can, of course, leave it to a professional who should not spend more than 20 minutes on it. Yet, you should know that maintenance operations are sometimes quite expensive, especially if you entrust them to an auto centre or car garage.

How to replace the spark plugs or glow plugs in your car?

If you have to replace the plugs yourself, you have to be careful and follow these steps:

    – Disconnect the battery.

    – Clean the area around the spark plugs before disassembling them to avoid dust falling into the engine during disassembly.

    – Remove and replace the spark plugs one by one to avoid swapping the ignition wires.

    – Disconnect the cables by pulling on the caps instead of pulling on the wires directly.

    – Unscrew the spark plugs with the spark plug wrench.

    – Remove them from the cylinder head and check that there is no grease or dust in the spark plug housing.

    – Put the spark plugs back into the cylinder head and start screwing them in by hand to ensure a good thread.

    – Finish screwing it in with a wrench, ensuring it has been aligned correctly in the thread.

    – Be careful to keep the wrench in line to avoid breaking the porcelain.

Car maintenance can be costly, so it would help if you can replace them by yourself. To limit this bill, you can check the price of spark plugs at various sale points as their cost may vary significantly from one seller to another.

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