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Spark Plug Blew Out of Head [Key Reasons and How to Fix]

Hi, I'm Azim Uddin, a student who loves cars. Visit to learn about car maintenance for beginners and experts. In my studies, I found a cool connection between hosting and car care. Join me on this journey where every road has a story, and hospitality meets the thrill of cars. Explore, learn, and enjoy the ride with me!

Hi, I'm Azim Uddin, a student who loves cars. Visit to learn about car maintenance for beginners and experts. In my studies, I found a cool connection between hosting and car care. Join me on this journey where every road has a story, and hospitality meets the thrill of cars. Explore, learn, and enjoy the ride with me!

Last Updated on May 10, 2024 by Azim Uddin

A jolting explosion disrupts the sweet harmony of a motor vehicle. What is it, you may wonder. Little does you know the spark plug has blown out of the cylinder head.

So, why does a spark plug blow out of the head? An over-tightened or loosely threaded spark plug to the cylinder head blows it out in the long run. The pressure from the combustion hits the plug hard and eventually squeezes it out. Worn-out thread path and engine overheating can also drive the spark plug out of the head.

With that being said, predominantly, it all boils down to the installation of the plug in the first place. Let’s explore this matter in broad detail, including how to fix or avoid it.

Spark Plug Blew Out of Head

What Causes A Spark Plug to Blew Out of Head?

The spark plug blows out of the head primarily due to a failure in the threaded connection between the plug and the cylinder head.

Installing a spark plug too tightly to the cylinder head can cause it to blow out. This is commonly found in engines with aluminum cylinders due to their softness.

When the plug is tightened beyond the recommended torque specifications, numeral problems arise. To begin with, too much pressure on the threads distorts them. Both on the plug and the head.

As a result, the grip between the plug and the head becomes weak, and it is vulnerable to vibration and combustion pressures. Hence, it blows out.

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During operation, repeated cycles of combustion generate force within the cylinder. And when the plug lacks thread engagement, it gradually loosens up. Consequently, it causes it to come out.

The engine’s constant heating and cooling cycles wear out the metal threads. Also, metal components expand due to heat. So, they stretch out and grow in size.

Now, as the engine cools down after extreme heat up, metal contacts, especially the head and the plug, lose integrity. And with further pressure from the combustion comes out as a troublemaker.

The result? Well, the infamous spark plug pops right out.

How Would You Know That Spark Plug Is Blown Out?

blown-out spark plugs with observation

It’s possible to detect blown-out spark plugs with careful observation. They are —

  • Engine misfire is the most common and predominant sign of a blown-out spark plug. You’ll notice jerky movement when accelerating.
  • Hearing louder noises while starting your car or other vehicle can be due to a blown-out spark plug. It occurs because the air-fuel mixture does not mix correctly.
  • The drop in fuel efficiency may be traced back to a blown-out spark plug. You’ll have decreased mileage per gallon of fuel.
  • Rough idling is a sign of a spark plug snuffed out. Your vehicle will ridiculously vibrate when stationary.
  • An Engine refuses to start when the spark plug is cast out. You may also observe an increased cranking period.
  • Emission from your vehicle significantly increases when an engine’s spark plug is blown out.

How to Fix Spark Plug Blew Out of Cylinder Head?

location of spark plug

Figure: Location of Spark Plugs

See also  Spark Plug Blew Out of Engine: Why and How to Fix It?

Source:  YouTube

The blown-out spark plug can be fixed by replacing it altogether. You can attempt to reinstall it again, or you can get help from car mechanics.

You see, the repair shop will charge $300 to $500. But in terms of replacing the plug, if you do it yourself, it will save you the labor cost.

  1. Turn off the engine and let it cool down first. Use safety gear such as gloves and goggles.
  2. Locate the spark plug on your vehicle. For example, you’ll need to pop the front hood of a car and follow the spark plug wires to find it. Use your car’s manual to get some help.
  3. Inspect the plug threads and the cylinder head. Check whether any sign of cross-threading or damage is present.
spark plug

Figure: Cross-Threaded Spark Plug

Source: Reddit.

Clean the plug and the cylinder thoroughly. Remove dirt, oil, and gunk. You can use a thread chaser to clean and straighten the threads.

  1. Check for cracks or stripped threads on the cylinder head. Try using a thread repair kit such as Helicoil. If you are not technically sound, get your vehicle to a repair shop.
  2. When you find the cylinder head in good condition, go ahead and install the new spark plug. Ensure it has the correct specifications, such as heat range and torque.
  3. Use a torque wrench to mount it properly. Let it go when you feel resistance. This way, your spark plug will not get over-tightened.

How Can You Prevent Spark Plug From Blowing Out?

Preventing Process Of Spark Plug From Blowing Out

Be one step ahead and prevent the spark plug from bursting out of the cylinder head. This will mitigate future hassle by an enormous margin.

See also  Spark Plug Blew Out of Engine: Why and How to Fix It?
  • Always install a spark plug that meets the manufacturer’s torque specification. Neither tighten it too much, nor it should be loose.
  • Use an anti-seize compound to spark plug threads and cylinder heads. This will facilitate future removal.
  • Ensure the threads of the head and plug are clean and devoid of dirt. Perform regular maintenance to safeguard this.
  • Verify the gasket condition every time you are about to change the vehicle’s spark plug. This will ascertain no fault in the gasket. This way, you can prevent possible compression leaks and blowouts.
  • Thread a spark plug into the cylinder head by hand to avoid cross-threading.
  • For those technically unversed or nervous about getting under the vehicle’s hood, always seek professional help when it comes to changing the spark plug.

Frequently Asked Questions

A zillion queries are floating on the internet in light of the spark plug blowout issue. Although you should not worry about every one of them, some of them are really important to pay attention to.

Is It Okay to Drive With a Blown Spark Plug?

No, you should not drive with the blown-out spark plug. It may not seem the type, but it will eventually create more serious issues such as catalytic converted destruction. Also, incomplete combustion will consume more fuel.

How Often Should Spark Plugs Be Changed?

The best answer for when you should change the spark plug is to follow the manufacturers’ suggestion. While some recommend changing after 18,000 miles, others may indicate a mileage of 30,000 or even 100,000.

Closing Thoughts

The blowout of a spark plug indicates the very important matters of meticulous installation, regular maintenance, and problem recognition. So be on the lookout for any sign of this issue and address it as quickly as possible. I know it can be too intricate even to dare to dive into the issue, but after reading this article, you are ready to take a shot. Don’t forget there are experts in your vicinity to help you nonetheless.

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