Glow Plug Testing Without Dismantling: A Simple Guide for Diesel Engine Owners


Diesel engines are well-known for their reliability and fuel efficiency. However, when the temperature drops, diesel engines may struggle to start, which can be caused by the failure of the glow plugs. Glow plugs play a critical role in diesel engines, and if they malfunction, they can cause a host of problems. In this article, we’ll discuss how to test glow plugs without dismantling them, the symptoms of worn , and the cost of changing them.

The Role of Glow Plugs

Glow plugs are heating elements that ignite the fuel in the combustion chamber of diesel engines. They work by heating up the air in the cylinder, which increases the temperature of the fuel and makes it easier to ignite. Glow plugs are essential to the starting process of diesel engines, especially in cold temperatures. They also help reduce emissions by ensuring complete combustion of the fuel.

How to Test Glow Plugs Without Dismantling

Testing glow plugs without dismantling them is a simple process that requires a few tools. You’ll need a multimeter, a battery, and a set of jumper wires. Here are the steps to follow:

  1. Switch off the engine and remove the key from the ignition.
  2. Locate the glow plug relay. It is usually located in the engine compartment and is connected to the battery.
  3. Disconnect the glow plug relay from the battery.
  4. Using the jumper wires, connect the positive terminal of the battery to the terminal on the relay that supplies power .
  5. Connect the negative terminal of the battery to a good ground point on the engine.
  6. Using the multimeter, test the resistance of each glow plug. The resistance should be between 0.5 and 2 ohms.
  7. If the resistance is outside the range, the glow plug is faulty and needs to be replaced.
  8. Repeat the process for each glow plug.

Symptoms of Worn Glow Plugs

When glow plugs start to wear out, they can cause a host of problems that can affect the performance of your diesel engine. Here are some common symptoms of worn :

  • Difficult starting: If the engine is slow to start or doesn’t start at all, it could be a sign of worn .
  • Rough idling: If the engine idles roughly, it could be a sign .
  • Engine misfires: If the engine misfires or hesitates when accelerating, it could be due to worn .
  • Increased smoke: If you notice an increase in smoke from the exhaust, it could be a sign of worn .

If you notice any of these symptoms, it’s important to have  checked as soon as possible to avoid further damage to your engine.

Cost of Changing

The cost of changing glow plugs varies depending on the make and model of your diesel engine. The cost  themselves can range from $20 to $50 each, and the labor costs can range from $100 to $300, depending on the complexity of the job. Overall, you can expect to pay anywhere from $200 to $600 for a complete glow plug replacement.


Glow plugs play a critical role in the performance of diesel engines. If you notice any of the symptoms of worn , it’s important to have them checked and replaced if necessary. Testing glow plug without dismantling them is a simple process that can be done with a few tools. Remember, if  are not working correctly, it can lead to further damage to your engine and decrease fuel efficiency.

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