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What causes a spark plug to blow out

Causes of Spark Plug Failure

A spark plug is key to an engine’s ignition system. But, it will break down eventually due to wear and tear. To stop this from happening, you need to understand what causes spark plug failure. Poor spark plug maintenance, low temperatures when firing, and pre-ignition can all cause problems.

In this section, we’ll discuss these causes and how to avoid them:

  • Poor spark plug maintenance
  • Low temperatures when firing
  • Pre-ignition


Pre-ignition is a major cause of spark plug failure. This occurs when fuel lights up earlier than the spark plug. It usually happens due to a very high temperature in the combustion chamber.

Reasons for pre-ignition and other spark plug damage include:

  • High compression: This increases cylinder pressure, forcing more fuel and creating heat. The spark is earlier than what the engine’s electrical system is designed for.
  • Detonation: This is an uncontrolled combustion due to pressure waves in the air/fuel mixture. It is caused by too much advance timing or an overly lean fuel mixture under load.
  • Overheated plugs: Using higher heat plugs for better performance can lead to overheating and spark plug failure. It is important to choose a heat range that fits the application and engine condition.
  • Carbon buildup: Excessive oil on or around the plugs causes carbon deposits. These deposits act as an insulator, reducing plug effectiveness. High temperatures weaken the conductive seals, leading to malfunction or failure. This should be addressed quickly or with regular maintenance such as oil changes and cleanings.


Spark plugs can get too hot if the engine runs at high speeds for a long time. Or in summer when it’s really hot. The heat can melt the parts inside the spark plug, making it fail. Tuning or modifying the air-to-fuel mixture in the engine can also lead to more heat and spark plug failure. Too much fuel and not enough air in the engine can cause the same problem.

Other signs of overheating spark plugs are deposits on the ceramic and a raised electrode design. It’s important to set the spark plug gap depending on the application, fuel type and modifications made to the vehicle. Usually, you only need to adjust the gap when replacing spark plugs or if there’s an internal combustion problem like too much carbon build up.

Carbon buildup

Carbon deposits can harm spark plugs. When fuel and air don’t ignite properly in the combustion chamber, carbon builds up on the electrodes. This causes problems, like pre-ignition, more fuel use, knocking, and misfires. These things shorten the life of the spark plugs and cause them to fail.

To reduce carbon build-up, follow your vehicle manufacturer’s maintenance schedule.

Diagnosing a Blown-Out Spark Plug

A spark plug might blow out for a few different reasons. These include wrong installation, damaged wire insulation, and too much carbon on the electrode. Before getting a new spark plug, it’s essential to find the source of the problem.

This article talks about the usual causes of blown-out spark plugs, and how to identify and fix them:

Visually inspect the spark plug

Visually inspect your spark plug for any cracks or damage. This may indicate an air leak, reducing the efficiency of your engine.

Use a spark plug tester to check if the electrical connections are made correctly and if there is any internal corrosion.

Inspect the ignition system components.

Measure the resistance of each wire with an ohmmeter. Compare the readings to the manufacturer-specified values.

If any exceed the values, the engine will struggle and spark plugs may be blown-out.

These steps can help diagnose issues and prevent them from occurring again:

  • Visually inspect your spark plug for any cracks or damage.
  • Use a spark plug tester to check if the electrical connections are made correctly and if there is any internal corrosion.
  • Inspect the ignition system components.
  • Measure the resistance of each wire with an ohmmeter. Compare the readings to the manufacturer-specified values.

Check for any fuel or oil residue

If you smell fuel or oil near the spark plug, it’s likely been affected. Use caution when examining it. Place a shop rag over the area and check for any signs of leakage. Don’t touch the plug itself. Also, check any gaskets or nearby parts for fuel or oil staining. If you spot any residue, clean it off with a degreaser or cleaner before continuing. This will help protect other parts and make sure your diagnosis is right.

Check for signs of improper gap

To diagnose a blown-out spark plug, first inspect it for improper gap. Use a feeler gauge and insert it between the terminals. The proper gap should be 0.028″ to 0.032″. Any other value means the gap needs adjusting.

Carefully examine the spark plug for damage. Look for broken or melted electrodes, carbon buildup near the terminals and discoloration due to heat. Damage can further damage your engine.

The most common cause of a blown-out spark plug is an oversized or misaligned gap. This can be caused by

  • incorrect installation or adjustment of the electrodes,
  • build-up of contaminants,
  • an incorrectly calibrated ignition system generating too much amperage.

This leads to overheating on either side of the electrode, causing erosion and eventual breakage. Without treatment, this leads to total failure.

Preventing Spark Plug Failure

Spark plugs can fail – but why? Let’s investigate! Common causes of spark plug failure include:

  • Incorrect installation
  • Incorrect spark plug gap
  • Inadequate lubrication
  • Spark plug fouling

To prevent spark plug failure, make sure to install correctly, set a proper plug gap, lubricate adequately, and avoid fouling.

Regularly inspect spark plugs

A spark plug is vital for any vehicle’s engine, so inspect it regularly. Pull it out and look for any oddities or damage. If there are jagged ends, broken pieces, or rust, change the spark plug ASAP. When putting it back, stick to the manufacturer’s instructions and use the right kind of gaskets, washers, and seals.

Other common causes of spark plug failure are:

  • Insufficient spark: Ignition timing off or electrodes worn down= air-fuel mix not combusting properly.
  • Oil contamination: Oil can creep into the combustion chamber and cover the electrodes in a thin layer of oil, blocking a good spark.
  • Carbon deposits: Unburnt fuel in the combustion chamber builds up on the electrodes, lessening their effectiveness.
  • Heat: Too much heat in the combustion chamber wears down the insulator nose and electrode tip.
  • Oversized gaps: Spark plugs gapped too wide stop a complete circuit forming.

Use the correct spark plug for your engine

Using the wrong spark plug with an engine can cause failure. The spark plug must be heat-resistant and corrosion-resistant. So, the recommended spark plug for a particular engine must be followed.

For a four-stroke engine, use an AC R45T resistor spark plug. It saves energy, reduces radio interference and helps cold starting. For two-stroke engines, copper or platinum tipped plugs are used.

The gap between the electrodes needs to be the right size. This depends on the type of engine, the compression ratio, displacement, weight of car, fuel used, and climate. It’s important to get the right gap size for the application. Every vehicle and application has its own specific requirements.

Change spark plugs at the recommended intervals

Spark plugs are essential for engine performance. They fire off sparks to ignite the air-fuel mixture. It’s important to change spark plugs regularly at intervals recommended by the vehicle manufacturer. Not doing so can cause serious engine damage.

The duration of spark plugs varies, typically between 30,000 and 70,000 miles. Some modern engines use long life spark plugs with intervals of over 80,000 miles. Check the owner’s manual or ask a mechanic for the right replacement interval for your vehicle.

If you’re changing the spark plugs yourself, select the correct type and gap them according to manufacturer specifications. Inspect the spark plugs for discoloration before reinstalling them. Lastly, use anti-seize lubricant to ensure that they don’t stick while installing or removing them.


A spark plug blowout can be caused by multiple things. Often, it’s due to high engine compression, a bad spark plug, or too much heat in the combustion chamber. Other components which can result in failure are the incorrect gap setting, an unsuitable spark plug, or even a defective one. Thus, it is difficult to figure out precisely why a spark plug has blown out.

Spark plug failure can be caused by a variety of factors

Spark plug failure can be caused by three factors: improper gap, incorrect heat range selection, and inadequate cooling.

  • Improper gap occurs when the electrodes aren’t set right apart. This can cause either too weak or too strong an arc. This leads to incomplete combustion or engine misfiring.
  • Incorrect heat range selection results in overheating. This can cause engine misfiring or pre-ignition.
  • Poor cooling leads to a buildup of carbon deposits and a high voltage which breaches the spark gap.

It’s essential to understand all three factors to identify the cause of spark plug failure. Once identified, you can take steps to resolve the issue and extend the life of engine components.

Regular inspection and maintenance can help prevent spark plug failure

Spark plug inspection and maintenance is key to maintain your car’s performance. Spark plugs can be damaged by heat, friction, fuel and engine contaminants over time. So regular cleaning and tuning is essential. Worn spark plugs can cause misfiring, rough idle or poor acceleration. This will result in decreased fuel efficiency and slower acceleration.

Inspect spark plugs regularly for signs of wear or fouling. Replace the spark plugs every 30,000 miles or as suggested by your manufacturer. This will help keep your vehicle running at peak efficiency for longer. Simple preventive car maintenance steps are important.

If you suspect a spark plug has blown out, it is best to have it inspected and replaced by a qualified mechanic.

Once you find that a spark plug is damaged, it is important to have it checked and replaced by a qualified mechanic immediately. Damage to spark plugs may cause misfires, loss of power and even damage to the catalytic converter. Other signs of a broken spark plug include hard starting, rough idling, and higher fuel consumption.

When you need to replace the spark plugs in your vehicle, there are some things to consider:

  • It depends on the make and model, age of your car, driving conditions, and environment.
  • Your mechanic will know what type of spark plugs to use.
  • Most modern vehicles use platinum tipped plugs instead of copper tip ones.

In conclusion, replacing failed spark plugs should be done by a qualified mechanic. This will ensure optimal engine performance and no damage to related components like the catalytic converter or fuel economy.

Frequently Asked Questions

Q: What causes a spark plug to blow out?

A: A spark plug can blow out due to excessive heat, pre-ignition, or detonation. Excessive heat can be caused by an incorrect heat range, incorrect gap setting, or an incorrect installation. Pre-ignition and detonation can be caused by an incorrect fuel-air mixture, incorrect ignition timing, or an engine running too hot.

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