Glow Plugs replacement & repair made easy

Glow plugs were originally used to assist with starting diesel engines in cold temperatures when the heavy oil used to coagulate. Now that diesel has many additives to prevent this, glow plugs have taken on the role of heating the incoming fuel / air mix to provide greater efficiency while the engine warms up. This also assists with decreasing the noise during cold running.

• The mechanic will pre-soak the glow plug threads with penetrating oil or similar and wait for it to take effect.
• Mechanic will then ease the glow plugs undone and remove them one by one
• New glow plugs will then be installed
• Engine start up will be tested and error codes cleared down

Unless you are a qualified mechanic with the required skills, training and equipment to do the job, we strongly recommend a glow plugs replacement is only carried out by a professional mechanic. ClickMechanic can help get you a vetted and local mechanic to carry out the work. Just enter your postcode and your car's registration number at the top of this page and select the work needed to get an instant fixed price up front.

You may experience some of the following symptoms

• Glow plug warning light flashing when the ignition is switched on
• Engine management warning light (EML) lit
• Struggling to start from cold
• Excessive fuel consumption while the engine warms up

On average, glow plugs replacement times can range from 1 to 2 hours with an average of just over 1 hours. The time that the job takes will depend on a number of factors, like your vehicle's make and model, year, as well as other factors. Select your car at the top of this page for information on job time and cost for your vehicle through ClickMechanic.

The majority of diesel vehicles will go through their life without requiring them to be changed, however like all electrical units, they can fail. If you are experiencing any of the listed symptoms, ideally would have the glow plugs changed as soon as possible. If the engine is starting OK, though and there is no EML lit, then get the glow plugs changed when you are able to.

If you suspect there is any issue with the glow plug or there are concerns about its age or condition, book an inspection with a professional mechanic with immediate effect. If the glow plug is physically broken or snapped do not drive the vehicle as this will lead to severe engine damage.

The glow plug warning light provides information on whether the glow plug has warmed up, and whether there is a problem with it. When the ignition is switched on the glow plug warning will come on as the glow plugs through it's pre-heat cycle, the light will go off again once the glow plugs have heated up.

If the glow plug warning light does not go off it means that the engine is not getting the right amount of heat from the plugs, which can affect starting and performance. If the glow plug warning light is flashing it means that the glow plugs are not getting hot enough to start the car and that there is a problem. This can be caused by a number of things.

Generally it is ok to continue to drive at slower speeds with a flashing glow plug warning light, however, it does entirely depend on the scale of the glow plug issue. Often the engine also goes into 'limp mode' and power will be limited. It is highly recommended to get it checked by a qualified mechanic as soon as possible as it could lead to further problems and engine damage.

In rare cases the engine warning light may also flash simultaneously with the glow plug warning light, which can indicate an overheating engine. When this happens, the best thing to do is stop as soon as it is safe to do so and seek help from a breakdown service or a qualified vehicle technician

Yes, it is possible that a flashing glow plug warning light may lead to an MOT fail. The underlying issue may lead to inefficient running of the engine and an emissions issue, on which a vehicle may be failed.

Yes, a faulty glow plug may result in an MOT failure - if the glow plug warning light on the dashboard goes off after a few seconds then it will normally pass the MOT (this is a sign the plugs have heated up correctly). If the warning light continues to flash or illuminate on the dashboard, it could result in an MOT failure as your vehicle may experience emissions issues.

You can expect glow plugs to last at least 100,000 miles but they can become faulty at an earlier stage so may need replacing accordingly.

Glow plugs can be very hard to replace, especially if they are located in hard to reach location or in the case they are seized or stuck. The job best left to a certified mechanic as it needs the right parts and equipment to ensure the replacement is done properly. If a glow plug breaks on removal, an bits drop into the inside of the engine this will lead to the engine having to be opened up. Under no circumstances should the vehicle then be started as it can lead to catastrophic engine damage.

You need one glow plug for each cylinder in your engine so a 4 cylinder diesel engine will need 4 glow plugs.

Some tell-tale signs that your glow plugs may need changing include:

• Engine misfiring
• Rough idling
• Decrease in fuel efficiency
• Difficulty starting the car (especially in cold weather)
• Dark or black-coloured exhaust smoke