Spark Plug Blew Out of the Cylinder Head (Causes and How to Prevent)

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When you’re driving down the road, the last thing you expect to happen is for the spark plug to shoot out of your engine.

But what the heck does it mean when the unexpected happens and the spark plug is no longer in your engine? More importantly, how do you fix it and how much will it set you back?

Before you take your vehicle to a mechanic or attempt to fix it yourself, read this guide. There’s a lot of misinformation out there about spark plug blowouts, and we want to help get you the right information before a shady mechanic tries to rip you off.

spark plug blow out

What is a Spark Plug Blow Out?

Spark plug blowout is a problem that primarily affects select Ford vehicles. What happens is that the spark plug actually blows straight out of the cylinder head.

It usually stays attached to the coil wire, but since it’s no longer inside the combustion chamber it’s not working at all. It’s a well-known problem for select Ford vehicles, especially their 4.6L, 5.4L, and 6.8L engines.

But keep in mind that while it’s far more common for these vehicles, it’s not the only vehicle it can happen to. And because it’s a common problem for those Ford vehicles there are easy-to-access repair kits out there.

If it happens to another type of vehicle, finding the right repair kit might be a little more challenging for you.

What Causes a Spark Plug Blow Out?

blown out spark plug

While there are a couple of potential causes for a spark plug blowout, the most common reason by far is that the spark plugs were a little loose after you installed them. Over time the spark plugs will back out further, and eventually there won’t be enough threads to hold them in place.

When this happens the spark plugs shoot out of the holes when the engine is running. Compounding the problem is that some older maintenance manuals for specific Ford vehicles list torque specs that are a bit too low.

These manuals request a torque spec around 20 ft-lbs, while newer service manuals recommend between 28 and 30 ft-lbs. If you use the lower torque spec, you run the risk of the spark plug blowing out of the cylinder head down the road.

There could be an overabundance of pressure inside the combustion chamber, but this is really only a problem if you put a ton of performance parts on your vehicle. And even then, the freeze plugs should crack before the spark plugs.

Finally, while some guides state that over-torquing the spark plugs can cause them to blow out of the cylinder head, we don’t see how that could happen. Over-torquing the spark plug runs the risk of cracking or destroying the spark plug itself, but it shouldn’t blow out of the cylinder.

See Also: DIY Car Repair Tools – Torque Wrench

How Can You Tell If You Have a Blown Spark Plug?

While some guides list a ton of symptoms of a blown spark plug, this is another area where you really don’t have to worry about doing much diagnosing.

That’s because when your engine blows a spark plug out of the cylinder head, it sounds like a gun going off.

It’s loud and extremely noticeable, and anyone near the vehicle when it happens will notice. Not only that, but when the engine is running it’s going to sound awful if it’ll even run. And that’s just for one blown spark plug.

When you look under the hood, you’ll find the spark plug dangling by the wire, making it a pretty easy problem to diagnose.

Here’s what it sounds like when driving:

How Do You Fix a Blown Out Spark Plug?

spark plug blow out repair kit
CalVan Tools repair kit

If you take your vehicle to a professional shop for repairs, there’s no telling how much they’ll try to charge you. Some shops will get you in and out for about $800, while others will charge you closer to $4,000 and try to replace the entire heads.

With that in mind, it’s a good idea to know how to fix the problem to begin with. There’s actually a specific repair kit for this problem, and it comes with everything you need.

The kit lets you rethread the blown-out spark plug hole, and then there’s a sleeve you install so you can put in the new spark plug.

Don’t just put the spark plug back in or you risk it blowing out again. Furthermore, use the correct torque spec for the sleeve to keep the problem from happening again.

What Will It Cost to Fix?

Shops will typically charge you between $800 and $1,000 to fix an engine with a blown-out spark plug. But if you’re willing to put in the work yourself and buy the repair kit you need to complete the job, you can expect to spend between $250 and $600, depending on the engine.

The price difference here all comes down to the price of the tool you need. Different engines require different tools, so you’re really out of luck trying to shave any costs here.

How to Prevent Spark Plug Blow Out

install spark plug with torque wrench

You really don’t want your spark plug blowing out of the cylinder head, and prevention all comes down to using the right torque specs to install spark plugs the right way. Don’t use the lower torque specs in older Ford service manuals.

Other guides will recommend more frequent torque checks of the spark plugs, but if you use the right torque specs the first time, this is completely unnecessary. Not only that, but if you’re paying a mechanic to do it for you then you’re wasting money, and if you’re doing it yourself you’re wasting a lot of time.

Moreover, don’t use anti-seize or any other lubricants on the spark plugs when installing them. This can throw off the torque spec, which is really your only defense at preventing a spark plug blowout.

Can a Glow Plug Blow Out on a Diesel?

While it’s possible for a glow plug to blow out of a diesel engine, it’s a pretty rare occurrence. Moreover, the most common reason for a glow plug to blow out of a diesel is for the compression to get too high in the compression chamber.

That’s the most likely reason, but if you don’t torque the glow plugs down correctly when installing them, they can blow out just like a spark plug.

But since there’s not a well-known issue surrounding misinformation and glow plug torque specs, mechanics usually install them correctly the first time.

Adam Mann

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