Glow Plug Guide

In diesel engines, metal or ceramic glow plugs play a crucial role in the engine starting process, ensuring efficient combustion and optimal engine performance. Understanding what glow plugs are, how they function, and recognising signs they need replacing is useful knowledge for any diesel vehicle owner.

Our Glow Plug Guide provides comprehensive information for diesel vehicle owners. It outlines the significance of glow plugs in diesel engines, detailing their types, functions, and the number of plugs typically found in vehicles. The guide also discusses signs indicating the need for glow plug replacement and offers fault-finding techniques. It covers a range of potential issues, such as damaged or missing probes, and provides corresponding solutions.

Additionally, step-by-step instructions for changing glow plugs are included, ensuring owners can address issues efficiently.

What are glow plugs?

Glow plugs are found in diesel engines. Unlike spark plugs in petrol engines, glow plugs aid in the combustion process by generating heat within the combustion chamber. Typically installed in the cylinder head, these plugs serve a vital function, especially in cold weather conditions where diesel fuel tends to gel.

Types of glow plug

1. Metal Glow Plugs: These are the traditional type of glow plugs, consisting of a heating coil encased in a metal sheath. They are known for their durability and are commonly used in older diesel engines.
   
2. Ceramic Glow Plugs: These glow plugs use a ceramic heating element instead of a metal coil. Ceramic glow plugs can reach higher temperatures faster than metal plugs, making them ideal for modern, high-efficiency diesel engines. They are more efficient in colder climates and reduce the engine's warm-up time.
   
3. Quick-Start Glow Plugs: Designed for rapid heating, quick-start glow plugs can reach optimal temperatures within a few seconds. This feature is particularly beneficial in extremely cold environments, ensuring that the diesel engine starts quickly and reliably.
   
4. Post-Heating Glow Plugs: These glow plugs continue to operate after the engine has started, helping to reduce emissions during the warm-up phase. They are particularly effective in reducing the amount of unburned fuel and particulate matter in the exhaust, making them suitable for engines designed to meet stringent emission standards.
   
5. Pressure Sensor Glow Plugs: A more advanced type, these glow plugs incorporate a pressure sensor that provides feedback on the combustion process. This information can be used to optimise engine performance, improve fuel efficiency, and reduce emissions.
   
6. Double Filament Glow Plugs: These feature two heating elements and offer a combination of rapid heating and post-heating functions. They provide quick start-up times and continue to contribute to efficient combustion and reduced emissions during the initial phase of engine operation.
   
7. Regulating Coil Glow Plugs: Equipped with a regulating coil, these glow plugs can adjust their temperature based on the engine's requirements. This adaptability helps in achieving optimal combustion conditions over a wide range of operating scenarios.

Each type of glow plug has its specific advantages and is selected based on the requirements of the engine, the ambient conditions, and the desired performance characteristics. Modern diesel engines often use advanced glow plugs like ceramic or pressure sensor types to meet higher efficiency and emission standards.

How do glow plugs work?

The fundamental function of a glow plug is to preheat the air within the combustion chamber before starting the engine. When the ignition is turned on, an electrical current flows through the glow plug, causing it to heat up. This heat, in turn, warms the surrounding air and the diesel fuel, promoting easier ignition when the engine is cranked. Once the engine reaches a certain temperature, the glow plugs switch off, and the combustion process continues through the engine's normal operation.

H2: How many glow plugs are in a car?

The number of glow plugs in a vehicle will depend on the type of engine. In most diesel vehicles, there will be one glow plug per cylinder, but this will vary depending on engine design and quality, and manufacturer. This information will be outlined in the owner’s manual.

Signs it's time to change your glow plugs

Like any component, glow plugs are subject to wear and tear over time. Noticing signs that show when a replacement is needed can prevent unexpected problems and damage to your diesel engine.

1. Extended Cranking Time:

If your diesel engine takes longer to start, it could be an indication that the glow plugs are not providing sufficient heat. This is often more noticeable in colder weather when the engine requires additional assistance in achieving optimal combustion temperatures.

2. Rough Idling:

Faulty glow plugs can lead to uneven combustion, resulting in a rough idle. If you notice increased vibrations or a shaky engine when idling, we recommend checking the glow plugs.

3. Excessive Smoke:

A diesel engine emitting excessive smoke during startup or under normal use may be a sign of inefficient combustion. Faulty glow plugs can contribute to incomplete combustion, leading to the production of more smoke than usual.

4. Decreased Fuel Efficiency:

Diminished fuel efficiency is often linked to suboptimal combustion. If your diesel vehicle starts to have reduced miles per gallon, it could be a sign of glow plug issues.

5. Warning Lights:

Modern diesel engines are equipped with onboard diagnostic systems that can detect issues with various components, including glow plugs. If the engine management light illuminates on your dashboard, it's advisable to have your vehicle inspected, as it may signal a problem with the glow plugs.

Glow plug fault finding

Identifying the root cause of glow plug issues involves a systematic approach to fault-finding. Here are some steps to help diagnose potential problems:

1. Check for Fault Codes:

Modern diesel vehicles are equipped with onboard diagnostic systems that can provide error codes related to the glow plug system. Use a diagnostic tool to retrieve these codes and pinpoint the specific issue.

2. Visual Inspection:

Inspect the glow plugs visually for any signs of physical damage or excessive wear. A damaged glow plug may not function correctly, affecting the overall performance of the engine.

3. Test the Resistance:

Using a multimeter, measure the resistance of each glow plug. A significant deviation from the specified resistance values could indicate a faulty plug. It is important to compare the measured resistance with the manufacturer's specifications for the glow plugs to determine if they are within the acceptable range. If the resistance values deviate significantly, it may be necessary to replace the faulty plug to restore optimal engine performance.

4. Voltage Test:

Check the voltage supply to the glow plugs during the preheating phase to ensure optimal heating for smooth starting. Insufficient voltage can cause inadequate heating, which may result in difficulties when starting the engine.

5. Inspect the Wiring:

Inspect the wiring and connections related to the glow plug system. Corroded or damaged wiring can disrupt the electrical flow and impact the efficiency of the glow plugs.

Visual fault finding guide

Here are some potential problem causes and solutions; thanks to ignition experts Denso for the photos:

Enlarged Probe Tip

Potential Causes:

• Excessive voltage
• Alternator and regulator failure
• Damp storage conditions

Remedial Actions:

• Verify onboard and Glow Plug voltage
• Inspect the charging system
• Assess the quality of storage conditions

Fractured Probe Tip

Potential Causes:

• Excessive glowing or voltage
• Alternator or regulator failure

Remedial Actions:

• Inspect contacts on glow plug regulator
• Verify onboard and Glow Plug voltage
• Check charging system voltage

Deteriorated or Absent Probe Tip

Potential Causes:

• Ignition Unit Failure
• Incorrect Fuel Jet Direction or Regularity
• Sealing Fault Resulting in Spraying Position Error

Remedial Actions:

• Ensure correct installation of the ignition unit
• Verify usage of the appropriate ignition unit for the vehicle model
• Inspect Glow Plug installation point for carbon deposits

Distorted Probe (Overheating)

Potential Causes

• Ignition unit failure
• Incorrect fuel jet direction or regularity
• Faulty sealing leading to incorrect spraying position
• Excessive glowing or voltage
• Alternator and regulator failure
• Injection unit malfunction or timing issue

Remedial Actions:

• Ensure correct installation of the ignition unit
• Verify usage of the appropriate ignition unit for the vehicle model
• Inspect Glow Plug installation point for carbon deposits
• Check contacts on Glow Plug regulator
• Verify onboard and Glow Plug voltage
• Examine charging system voltage
• Review fuel injection timing

Swollen ring on the probe tip

Potential Causes

• Presence of oil in the combustion chamber

Remedial Actions:

• Check piston clearance in engine cylinders
• Check and assess oil consumption

Probe Missing

Potential Causes

• Ignition unit failure
• Incorrect fuel jet direction or regularity
• Faulty sealing resulting in wrong spraying position
• Malfunction or timing issue in injection unit
• Tread damage to opening of cylinder head where glow plug is installed
• Insufficiently tightened glow plug leading to incorrect seating

Remedial Actions:

• Verify usage of the correct ignition unit
• Ensure correct installation of the ignition unit
• Inspect Glow Plug installation point for carbon deposits
• Review timing of injection pump
• Assess the opening of the cylinder head

Probe touching body of glow plug

Potential Causes

• Over tightened torque
• The wrong tool used
• Thread damage to opening of cylinder head

Remedial Actions:

• Inspect the opening of the cylinder head for damage
• Check Glow Plug torque

Holes, cracks or melting next to body of Glow Plug

Potential Causes

• Failure of ignition unit
• Thread damage to the opening of cylinder head where Glow Plug is installed
• Insufficiently tightened Glow Plug causing improper seating

Remedial Actions:

• Verify timing of injection pump
• Inspect the opening of the cylinder head for thread damage

Carbon deposits between probe and body of Glow Plug

Potential Causes

• Failure of ignition unit
• Incorrect direction or regularity of fuel jet
• Faulty sealing leading to improper spraying position
• Failure in operation of injection pump

Remedial Actions:

• Ensure correct usage of the ignition unit for the vehicle model
• Verify correct installation of the ignition unit
• Inspect the Glow Plug installation point for carbon deposits
• Check the opening of the cylinder head for carbon fouling
• Review timing of injection pump

Broken or Bent power terminal

Potential Causes

• Over tightened torque
• The wrong tool was used (or the right tool was used wrongly)
• Thread damage to opening of cylinder head

Remedial Actions:

• Inspect the opening of the cylinder head for damage
• Check Glow Plug torque

How to change your glow plugs

If you've found a glow plug issue and need to replace it, follow these steps:

1. Get the Right Tools:

Before starting, make sure you have all the necessary tools, replacement glow plugs, and any additional components required for your particular vehicle model.

2. Locate the Glow Plugs:

Identify the location of the glow plugs on your engine. Consult your vehicle's manual if necessary for guidance on their exact placement.

3. Remove the Old Glow Plugs:

Using the appropriate tools, carefully remove the old glow plugs. Exercise caution to avoid damaging surrounding components.

4. Clean the Glow Plug Holes:

Before installing the new glow plugs, clean the plug holes to ensure a proper fit. Use a suitable cleaning tool or compressed air to remove any debris.

5. Install the New Glow Plugs:

Carefully insert the new glow plugs into their respective holes, ensuring they are securely seated. Tighten them to the manufacturer's specified torque settings.

7. Start the Engine:

Start the engine to ensure the new glow plugs are functioning correctly. Monitor for any warning lights or unusual engine behaviour.

8. Test Drive:

Take your vehicle for a test drive to confirm that the glow plug replacement has resolved any starting or performance issues.

How long will glow plugs last?

Glow plugs generally last for around 80,000 to 100,000 miles. However, this will vary depending on driving style, quality of the product, and how they have been fitted.

Importance of quality glow plugs

Investing in high-quality glow plugs is key for optimal engine performance. Quality plugs ensure efficient combustion, reliable starts, and prolonged engine life. Choosing reputable brands and durable materials for glow plugs pays off in improved overall vehicle reliability and reduced maintenance costs.

Glow Plugs and Fuel Efficiency:

Well-maintained glow plugs contribute to complete combustion, enhancing fuel efficiency and reducing emissions. Keeping an eye on the condition of your glow plugs translates to a greener and more economical driving experience.

Glow Plug Lifespan:

While lifespan varies, proactive replacement before signs of wear ensures uninterrupted engine performance. Regular checks and adherence to manufacturer recommendations contribute to maximising the glow plugs' service life.

DIY Glow Plug Testing:

In a DIY glow plug test, you can use a multimeter to check the resistance of each glow plug. This can help you determine if any of them are faulty and in need of replacement. Regular testing and maintenance can help keep your engine running smoothly and efficiently.

Glow Plug Advice and Online Sales

If you need new glow plugs for your car, we can help! Use our spark plug and glow plug lookup tool to find the right glow plugs for your car.

If you have questions or would like some advice, get in touch with our technical experts via phone, email or chat.

• Phone: 01209 202944
• Chat: via www.opieoils.co.uk (office hours)
• Email: sales@opieoils.co.uk