Common Issues with Oil Filled Ignition Coils and How to Troubleshoot Them

by:Haiyan     2023-10-27

Common Issues with Oil Filled Ignition Coils and How to Troubleshoot Them


Ignition coils are essential components of an ignition system in vehicles. These small but powerful devices play a crucial role in reliable engine performance by converting low-voltage power from the battery into high-voltage power needed to ignite the fuel mixture. One type of ignition coil commonly used is the oil-filled ignition coil. While these coils are generally reliable, they can experience certain issues over time. This article will explore some of the common problems encountered with oil-filled ignition coils and provide troubleshooting tips to help diagnose and resolve these issues.

Signs of a Faulty Ignition Coil

A faulty ignition coil can have a significant impact on your vehicle's performance. Here are some common signs that indicate a defective oil-filled ignition coil:

1.1 Engine Misfires

One of the most apparent signs of a faulty ignition coil is engine misfires. If you notice your engine sputtering, hesitating, or running rough, it could be due to a malfunctioning coil. Misfires occur when the coil fails to generate the required voltage, leading to incomplete combustion in one or more cylinders.

1.2 Difficulty Starting the Engine

A faulty ignition coil can also cause difficulties with starting the engine. If you find that your vehicle takes longer to start than usual or struggles to ignite, it may be a result of an issue with the ignition coil. This problem particularly arises when the coil fails to provide the necessary spark to jump-start the engine.

1.3 Decreased Fuel Efficiency

Another symptom of a faulty ignition coil is decreased fuel efficiency. When the coil is not functioning correctly, the spark plugs may not fire at the optimal time, leading to inefficient combustion. As a result, your vehicle's fuel consumption can increase, and overall mileage may decrease.

1.4 Illuminated Check Engine Light

An illuminated check engine light can be an indication of various issues, including a faulty ignition coil. Modern vehicles have onboard diagnostic systems that can detect abnormalities in the ignition system and trigger the check engine light. If the light remains on, it is advisable to have your vehicle inspected by a mechanic and the ignition system tested.

1.5 Decreased Engine Power

A failing ignition coil can result in decreased engine power. If your vehicle feels sluggish or lacks the usual acceleration, it could be due to a weak spark caused by a malfunctioning coil. When the coil fails to generate the necessary voltage, the combustion process becomes compromised, affecting overall engine performance.

Common Issues with Oil-Filled Ignition Coils

While oil-filled ignition coils are generally reliable, they can develop certain issues over time. Here are some common problems often associated with these types of coils:

2.1 Internal Oil Leaks

One of the prevalent issues with oil-filled ignition coils is internal oil leaks. Over time, the seals and gaskets that ensure the oil remains contained within the coil can deteriorate or become damaged. When this happens, oil can leak out of the coil, affecting its efficiency and performance. Internal oil leaks can also cause electrical shorts, leading to coil failure.

2.2 External Oil Leaks

Similar to internal leaks, external oil leaks can occur when the seals or gaskets around the ignition coil fail. External leaks result in oil seeping onto the engine or other components, causing oil stains and potentially damaging nearby parts. It is essential to address external oil leaks promptly to prevent further complications.

2.3 Insulation Breakdown

Another issue that can arise with oil-filled ignition coils is insulation breakdown. The coil's internal insulation materials can degrade over time, causing electrical leakage or short circuits. Insulation breakdown can lead to weak or intermittent sparks, resulting in engine misfires, reduced power, and other performance problems.

2.4 Overheating

Oil-filled ignition coils can also experience overheating issues. The continuous exposure to high temperatures under the hood can lead to heat buildup within the coil. Over time, excessive heat can cause the electrical windings inside the coil to degrade and fail. Overheating can be caused by various factors, including restricted airflow, engine overheating, or a failing cooling system.

2.5 Connector or Wire Problems

Connectors and wires that provide the necessary electrical connections to the ignition coil can become loose, corroded, or damaged. Poor connections can disrupt the proper flow of electricity, leading to weak or intermittent sparks. Checking the condition of connectors and wires is crucial during troubleshooting and maintenance to ensure optimum coil performance.

Troubleshooting Tips for Oil-Filled Ignition Coil Issues

When troubleshooting issues with oil-filled ignition coils, it is essential to approach the process systematically. Here are some tips to help diagnose and resolve common issues:

3.1 Check for Oil Leaks

Inspect the ignition coil for any signs of oil leaks, both internal and external. Look for oil stains or puddles around the coil or any noticeable oil residue inside the coil's housing. If leaks are detected, replacing the faulty coil or repairing the seals and gaskets is necessary.

3.2 Test the Resistance

Using a digital multimeter, measure the resistance of the ignition coil's primary and secondary windings. Compare the readings with the manufacturer's specifications. If the resistance is outside the recommended range, it may indicate a problem with the coil, and it should be replaced.

3.3 Inspect for Damage or Wear

Carefully examine the ignition coil for any visible damage, such as cracks or physical wear. Insulation breakdown, overheating, or rough handling can contribute to coil damage. If any visible issues are found, replacement may be necessary.

3.4 Check Connectors and Wires

Inspect the connectors and wires connected to the ignition coil for any signs of corrosion, damage, or looseness. Clean corroded connectors and repair or replace damaged wires to ensure proper electrical connections.

3.5 Perform a Spark Test

Remove the spark plug wires from the ignition coil and use a spark tester to check for a consistent spark when the engine is cranked. A weak or intermittent spark indicates a faulty coil that should be replaced.


Oil-filled ignition coils are vital components that require regular maintenance and occasional troubleshooting. By understanding the common issues associated with these coils and employing the appropriate troubleshooting techniques, you can diagnose and resolve problems effectively. It is always advisable to consult a professional mechanic for complex issues or if you are uncertain about any aspect of troubleshooting and repair. Maintaining a healthy ignition coil will contribute to a smooth-running engine and reliable vehicle performance.

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