What are glow plugs?

When winter is approaching, checking the glow plugs should be just as important to the diesel owner as switching to snow tires. But why?

In a spark-ignition or gasoline engine, combustion is started by a spark from the spark plugs. Diesel engines, on the other hand, operate according to the principle of “auto-ignition”. Intake air is compressed in the cylinders, heating it to a temperature of up to 900°C. When fuel is injected into the cylinders, it ignites automatically as a result of exposure to the high temperature.

If the outdoor temperature is low, the engine, cylinder and ambient air are cold. The engine then needs glow plugs to start: they heat the combustion chamber within a matter of seconds to the necessary temperature – a process known as “pre-glowing”.

But modern glow plugs can do even more: they continue glowing until the engine has warmed up and combustion is automatic. This also ensures smooth operation of the engine and low emissions during cold starts. The smoke output alone is reduced by about 50 percent.

Therefore: the only way that a diesel owner can be sure that his car will not let him down when the temperature suddenly drops overnight is to make sure that the glow plugs are intact. Only then will the engine run smoothly and burn only as much fuel as necessary – while keeping emissions low.