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Why glow plugs are needed in a diesel car

May 22, 2023

The diesel engine does not need spark plugs: the fuel in the engine cylinders ignites itself due to compression. But this requires the fuel itself to have a certain temperature, i.e. not to be too cold. In cold weather the diesel fuel, even in winter, becomes thick, and the engine starts with great difficulty or does not start at all. Glow plugs are used to warm up the fuel and start it easily.

In the diesel engine, the fuel-air mixture is self-ignited due to the intense heating of the air during its compression in the cylinders. Until the temperature in the chambers reaches the desired value, the engine is in "cold start" mode. If the operating conditions are different from normal, the engine will take too long to start. To avoid this, glow plugs are used, the principle of which is similar to the immersion electric heater.

By design, there is a difference between the glow plugs with a mono coil and a double coil. The first ones have a simpler construction and are installed on most modern cars. By using only a single coil, they are easier to adjust for self-adjustment and the desired temperature. This design is more reliable and stable over time.

Double-coil glow plugs, on the other hand, allow for a better adjustment of the optimum temperature balance. However, for their creation, you need to carefully approach the process of selecting materials, because with the wrong material they can work unstably and collapse. The double helix is only now being introduced to mass use in diesel engines.

Image about glow plugs from

Basically, candles are made of identical materials. The only difference is the tip, which is glowing. It can be made of metal (iron, chromium, nickel) and ceramic alloy with high thermal conductivity. In the first case, the tip cavity is filled with a powder that will consist of magnesium oxide. In addition to thermal conductivity, it also performs a damping function – it protects the thin coil from motor vibrations. The ceramic version can actuate as quickly as possible, so the driver can start the engine almost immediately after turning the key in the ignition. Cars that meet environmental standards and are equipped only with ceramic plugs. In addition to having a long service life, they ensure maximum combustion of the air-fuel mixture, even in a cold engine.

Glow plug failures in diesel engines

The service life of a glow plug depends on its design features, electrode material and operating conditions. Pin designs have an average life of up to 30 thousand kilometers of run, but some of the highest quality are able to provide trouble-free operation up to 60 thousand kilometers of operation.

It is best to perform a check for faulty spark plugs in a diesel engine before the onset of cold weather, as problems may not show up at all in the summer. The most common failures of this element are:

● Breakage of the coil;

● Destruction or melting of the heating rod;

● Damage to the threads of the mounting connection.

Replacement of glow plugs in the diesel passenger car is as follows:

The car is placed on a flat surface, the hood is opened. The decorative plastic cover of the engine is removed. Unscrews the fasteners and removes the upper cover of the cylinder head. From the glow plugs are removed from the contact wires, to unscrew the plugs will need a standard pipe wrench. New plugs are installed in place of the old ones. The remaining operations are performed in reverse order of disassembly. It should be noted that before replacing glow plugs, you need to make sure that the fault lies in them. Perhaps the culprit is the contact control unit or the glow plug power wire. You can assess the serviceability of the glow plug with the help of a tester or ammeter. In addition, modern engine control units have a diagnostic function, and can display an error code reflecting the defect in the glow plug.

Information about how to change glow plugs

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