Detecting Faulty Glow Plugs in Diesel Cars: Common Signs and Testing Methods

For diesel car owners, understanding and identifying signs of potential issues with glow plugs is crucial for maintaining optimal vehicle performance and ensuring reliability, especially in colder weather. Glow plugs play a vital role in assisting the diesel engine to ignite the fuel and start the car. Understanding how to recognize and test faulty glow plugs can save you time, money, and prevent potential damage to the engine.

Common Signs of Faulty Glow Plugs

Here are some common signs to look out for that indicate your diesel car's glow plugs may be faulty:

Hard Starting

One of the most noticeable signs of a problem with glow plugs is difficulty starting the engine, especially in cold weather. If your vehicle struggles to turn over or takes longer than usual to start, it is a strong indicator that the glow plugs may not be functioning properly.

Rough Idle

Another symptom is a rough or inconsistent idle, especially when the engine is cold. If the diesel vehicle runs poorly immediately after starting, it could be due to the glow plugs not heating up the air-fuel mixture adequately.

Increased Emissions

Visually inspecting the exhaust for any signs of white smoke during startup is also a significant indicator. This smoke is usually indicative of a malfunctioning glow plug that is not providing sufficient heat to the combustion chamber.

Check Engine Light

In many cases, the vehicle's onboard diagnostic system will trigger a check engine light if it detects issues related to the glow plug system. This alert can be a valuable diagnostic tool for identifying potential problems with glow plugs.

Testing Glow Plugs

Testing the glow plugs provides a definitive way to determine if they are faulty. Here are some methods for testing glow plugs:

Visual Inspection

Begin by visually inspecting the glow plugs for any signs of damage, corrosion, or excessive wear. This can often be a clear sign that the glow plugs need to be replaced.

Multimeter Testing

Using a multimeter set to ohms can help you measure the resistance of each glow plug. A healthy glow plug typically has a resistance of 0.5 to 2 ohms. If the resistance is significantly higher or infinite, the glow plug is likely faulty and requires replacement.

Resistor Testing

Another simple test involves using a thickish grade wire to check the glow plugs. Connect one end of the wire to the live terminal of your battery and the other end to the top of each glow plug. If there are no sparks, the glow plug is likely faulty and needs to be replaced.

Practical Steps for Testing and Replacing Glow Plugs

Once you have identified a faulty glow plug, it's important to replace it to avoid further issues. Here are some steps to consider:

Removing the Glow Plugs

To remove the glow plugs, start by opening the bonnet and locating the glow plugs, which are typically on the top of the engine, with an insulated bus bar connecting them together. Remove the bus bar to access the individual glow plugs.

Warmth Test

Before removing the glow plugs, you can perform a temperature test. Turn the ignition to the glow plug position until the light goes off, and do not attempt to start the engine. Feel the sides of the glow plugs; if they are warm, they are functioning correctly. Replace the cold ones.

Testing with Multimeter

Using a multimeter set to ohms, measure the resistance of each glow plug. Any value in the hundreds or infinite indicates a faulty glow plug needing replacement.

Spraying Penetrating Oil

To facilitate easy removal, spray a good quality penetrating oil around the plug where it goes into the cylinder head. Repeat this process 2 days later and another 2 days after that. Use an appropriate socket on a wrench to remove the glow plugs gently, avoiding excessive force to prevent damage.

By following these steps, you can effectively diagnose and replace faulty glow plugs in your diesel car, ensuring reliable performance and smoother starting.