Using our site means you agree to the use of cookies and other technologies. Our cookie policy.

What happens when your glow plugs fail?

Charlotte Phillips, 29 days ago

3 min read

  • Advice
  • Maintenance
Glow plugs

WhoCanFixMyCar discusses what happens when your glow plugs fail, including what causes this problem and the common signs to look out for.

In the unfortunate event that your car’s glow plugs fail, you will likely find yourself reading through this blog to find out why. It’s important to be aware of the reasons why your glow plugs can fail and what to do if you find yourself in this situation.

Contents

Common reasons why glow plugs fail

Symptoms of failing glow plugs

Can your glow plugs fail your MOT?

Can faulty glow plugs make your exhaust smell?


Why do glow plugs fail?

Your glow plugs are essentially a heating element inside a diesel engine that heats up the fuel and air, causing a combustion process to occur. Your glow plugs reach extremely high temperatures and much like a light bulb, they can burn out over time. With that being said, an average glow plug will last roughly 100,000 miles, so you shouldn’t have to worry about your glow plugs failing very often.

Common reasons why glow plugs fail include:

  • Excessive carbon build up in your pre chambers

  • Folds and dents on the rod of the glow plug

  • Snapped or damaged tip of the glow plug

  • Excessive heat reaching the glow plug

  • High voltages reaching the glow plug

If you do encounter issues with your glow plugs, you will likely require the help of a trained mechanic to diagnose the root of the problem for you.


Symptoms of failing glow plugs

If you think you’re having problems with your glow plugs, it’s good to be aware of the common symptoms of glow plug failure so you can take your car to a local garage for the right problem.

The common symptoms of glow plug failure include:

  • A hard starting engine

  • Engine misfires

  • Decreased fuel efficiency

  • Glow plug warning light on the dashboard

  • White smoke when starting your car up

  • Black smoke when driving the car

Because some of these symptoms are very similar to other problems you can have with your car, it’s important that you get the help of a trained mechanic to diagnose the problem for you.


Can your glow plugs fail your MOT?

If your glow plug warning light is on when your car is in for its MOT, it won’t fail if it turns off after a reasonable amount of time and you may receive just an advisory. At the same time, if the light stays on for longer than expected, you can expect that your car will not pass its MOT as this would indicate a problem with your glow plugs.

With that in mind, the best thing to do is always take your car straight to a local garage as soon as your warning light comes on to get it checked out to avoid uncertainty.


Can faulty glow plugs make your exhaust smell?

It’s not uncommon to notice an unusual smell when your glow plugs are faulty. Your exhaust will produce white smoke when there is not enough heat to burn the fuel, which can often be paired with the smell of fuel.

Similarly you might notice black smoke coming from your exhaust. Black smoke is caused by an imbalance in the air-fuel ratio, which in turn exits the engine through the exhaust pipe and can create a smokey fuel smell.


Think you need a specialist to take a look at your glow plugs? There are hundreds of trained mechanics in our network who can diagnose the problem for you.