What Happens When Your Glow Plugs Fail?
Charlotte Phillips, 6 months ago
3 min read
- Engine
- Diagnostic
FixMyCar discusses what happens when your glow plugs fail.
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. This guide covers everything you need to know.
Contents
Common reasons why glow plugs fail
Symptoms of failing glow plugs
Why do glow plugs fail?
Glow plugs are heating elements inside a diesel engine that raise the temperature of the fuel and air, allowing the combustion process to happen. Your glow plugs reach incredibly high temperatures and, much like a light bulb, can burn out over time. An average glow plug will last roughly 100,000 miles.
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.
Symptoms of failing glow plugs
It’s good to be aware of the signs of glow plug failure so you can take your car to a local garage for the right problem.
Common symptoms of glow plug failure include:
A hard starting engine
Decreased fuel efficiency
Glow plug warning light on the dashboard
White smoke when starting your car upBlack smoke when driving
Because a variety of issues can cause some of these symptoms, it’s important that you get the help of a trained mechanic for an accurate diagnosis.
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 an advisory. At the same time, if the light stays on longer than expected, you can expect your car to fail its MOT, as this would indicate a problem with your glow plugs.
Given this, it's a good idea to take your car to a local garage as soon as the glow plug warning light illuminates. This proactive approach will help you avoid any uncertainties and ensure your car is in top condition for its MOT.
Can faulty glow plugs make your exhaust smell?
It’s common 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.
Do 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.
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