Glow Plugs replacement & repair made easy

What does a glow plug do?

Glow plugs are fitted to diesel cars only. Similar to spark plugs in petrol cars, they ignite the air-fuel mixture in the engine. Instead of building to a sudden spark, the glow plugs slowly heat up until they are at a point where they can naturally combust the air-fuel mixture in each cylinder. This allows the engine to work more efficiently and results in lower carbon emissions.

How do you know there is something wrong with the glow plugs?

Glow plugs start your car and remain hot to keep the engine working. A problem with the glow plugs will usually mean you can't start your vehicle, or the engine is less efficient. This depends on the number of cylinders affected, but you will notice a loss in miles per gallon and higher emissions.

When should you consider a glow plugs replacement?

Glow plugs, like spark plugs, should be maintained according to the manufacturer recommended service schedule. This will mean that the glow plugs are usually replaced every few years, and it will help keep the rest of your vehicle running just as smoothly.

What happens during a glow plugs replacement?

A mechanic will come to remove and replace the old glow plugs. The operation of the engine will be checked and if required the car will be taken for a test drive, to check if any adjustments are needed.

What happens if I don’t replace glow plugs?

Because they are subjected to great extremes of temperature, glow plugs often need to work very hard to generate enough heat to fire up your engine.
The biggest enemy which prevents glow plugs from working efficiently is the inevitable build-up of carbon (soot) around them which is a by-product of the fuel ignition process.

If you don’t replace your glow plugs, you might find that your engine starts to misfire, is more difficult to start in the cold, and produces more smoke from the exhaust.

Can I replace my own glow plugs?

Replacing your glow plugs is not a big task but you still need to be mechanically skilled to carry it out.

You will need the right tools, and may also have to apply quite a lot of force making it easy to get the job wrong and cause damage to either the plugs or the mountings they screw into.

The biggest concern when replacing glow plugs is to ensure you use just enough force to unscrew them. Due to constant heating and cooling of surrounding parts, glow plugs can become brittle and may shatter if too much force is used. Once the fragments of the ceramic get into other parts like the cylinder, you additionally need to disassemble it to clear it.

Always follow the manufacturer’s instructions when changing the glow plug, especially concerning the amount of torque you should use to tighten them in their housing. Screwing them in too tightly is likely to damage the ceramic parts used as a heat conductor.

How common is a glow plugs replacement?

Glow plugs typically last for up to 100,000 miles. But like lots of things in your car, the more you use them and the more harshly they are treated, the sooner they will wear out.

If you regularly try to start your car before they have reached the right temperature, you can put extra wear on your glow plugs.
Your car’s servicing schedule will recommend the intervals at which it should need glow plug replacement. And while there are many instances of the plugs lasting much longer than these recommendations, the suddenness with which they can fail means you could easily find yourself stranded.

What are common glow plug brands on the market?

Some glow plug brands which are most often recommended are Beru, Champion, NGK, Monark, and Denso.

Are there any differences between the glow plugs used in old and new vehicles, or between petrol, diesel or electric vehicles?

Glow plugs are only found in diesel vehicles, but there are different types of plug available depending on the size of your engine.
They vary depending on the amount of heat which is needed to get the compressed air inside the engine up to the right temperature for it to cause the fuel to ignite.

How to extend the lifetime of your glow plugs?

To keep your glow plugs clean, regularly check the area around your engine’s glow plug terminals, and clear away any soot or debris, using a soft-bristled brush.

This is the main cause of the need for early glow plug replacement because the longer you go between clearing off the build-up, the more baked-on it will get by all the heat the plugs generate.

If you regularly make short journeys in your car and are re-starting the engine at regular intervals, this too will have a detrimental effect on the life of your glow plugs. If your car only gets short runs, make a point of taking it for an extended drive at least once a week to warm the engine up thoroughly.
Very cold weather is the enemy of all diesel engines. If you live in areas with harsher weather and frost during winter, keeping your car under cover or parked in a garage can also help your glow plugs last longer.