picture of glow plugs and packaging

Glow Plugs 101 for Mercedes Diesel Cars: What Owners Need to Know

Owning a Mercedes diesel brings with it the promise of efficiency, durability, and high performance. However, maintaining your diesel engine in top condition requires a clear understanding of its various components, one of which are the glow plugs.

What are Glow Plugs?

Glow plugs are an integral part of a diesel engine. Unlike petrol engines, diesel engines do not use spark plugs to ignite the fuel. Instead, they rely on compression and heat. When you start a diesel engine, the air inside the combustion chamber compresses, increasing in temperature. In cold conditions, however, the ambient temperature might not be high enough to heat the air to a temperature that allows ignition of the diesel fuel efficiently. This is where glow plugs come in.

How Do Glow Plugs Work?

Glow plugs are pencil shaped and have a heating element at the tip. Electrical current passes through it when you turn the ignition key, causing electrical resistance. This resistance causes the tip to heat up to 1000℃ within a few seconds and glow, which in-turn heats the air in the cylinder to a sufficient temperature to ensure proper fuel combustion allowing the engine to start and car to run optimally.

heated glow plug

Why Are Glow Plugs Important?

Glow plugs are critical for several reasons:

  • Cold Starting: Without effective glow plugs, starting a diesel engine in cold weather can be difficult or impossible.
  • Engine Health: Proper ignition at startup helps in maintaining the health of the engine. Continuous misfires or improper combustion can lead to engine wear and damage over time.
  • Emissions: Efficient ignition thanks to well-functioning glow plugs helps reduce emissions from your car. Incomplete combustion can increase emissions of harmful pollutants.

Signs of Faulty Glow Plugs

Vehicle owners should be aware of signs that indicate failing glow plugs. These include:

  • Difficulty Starting: The most common symptom of a failing glow plug is trouble starting the engine, especially in cold weather.
  • Misfiring Engine: If the engine misfires on startup, it could be due to one or more glow plugs not heating properly.
  • White Smoke from Exhaust: White smoke on startup can be a sign of unburnt diesel, which means the glow plugs may not be heating the combustion chamber adequately.
  • Engine Light: Many modern vehicles will trigger the engine management light if there’s an issue with the glow plug system. In a Mercedes Sprinter or Vito, the Glow Plug light will illuminate on the dashboard before starting, indicating the pre-heating phase. If this Glow Plug light continues to illuminate after starting or whilst driving, it is indicative of a fault with the Glow Plugs.
glow plug dashboard light

Maintaining and Replacing

Glow plugs should be checked regularly as part of your vehicle’s maintenance schedule. With typical wear and tear a glow plug should last at least 160,000 kms, depending on usage and environmental conditions. Mercedes diesel owners should consult their owner’s manual or Eurostar Diesels mechanic to understand the specific maintenance schedule for their vehicle model.

Replacing glow plugs is a delicate job and should ideally be done by a professional, at Eurostar Diesels this task takes roughly 3 hours. Incorrect installation can lead to damaged threads in the cylinder head or incomplete combustion due to improperly fitted plugs.

In Conclusion

In conclusion, glow plugs are essential for the efficient and effective operation of Mercedes diesel engines, especially in colder climates. Aiding in heating up the air and fuel in the combustion chamber of the engine, ensuring that the diesel fuel ignites smoothly and easily when the engine starts. Understanding their function and recognising signs of failure are key components of ensuring that your Mercedes diesel vehicle runs smoothly and maintains performance over time.

The Team at Eurostar Diesels are here to help with any questions or concerns you might have including the glow plug light staying lit up after start up.

Book your appointment today or call our office: 03 8795 7997 (Hallam) or 03 9088 8980 (Sunshine West) to speak with our friendly team.