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Gasoline-powered internal combustion engines rely on spark plugs to ignite the air-fuel mixture inside the engine. Unfortunately, spark plugs eventually wear out as the gap between the center and ground electrodes widens. That’s why spark plug replacement is part of your vehicle’s recommended routine maintenance.

When the time comes to replace your car’s spark plugs, you might want to do the job yourself to save some money. But if you’re a first-timer, there’s a good chance you won’t know how much to tighten down the new spark plugs.

How Tight to Tighten Spark Plugs: What You Need to Know

There isn’t a one-size-fits-all answer as to how tight spark plugs should be. Many professional mechanics with years of experience can snug down a set of spark plugs based primarily on feel. However, if you’re new to spark plug replacement, you’ll want to be careful, as plugs that are either too loose or too tight can cause problems.

car spark plug in white isolated background
There isn’t a one-size-fits-all answer as to how tight spark plugs should be.

Most vehicle manufacturers recommend using a torque wrench to tighten the plugs to the factory torque (tightness) specifications. You can look up the torque specs in a repair manual or online repair database. In some cases, you might also be able to find the information via an online search, but be careful—free information isn’t always good information.

One thing to keep in mind is that the torque specifications from the vehicle manufacturer are typically for new plugs. If you’re installing a set of previously used plugs, you might want to double-check with the spark plug manufacturer for the exact torque specifications.

Also, applying anti-seize (or any other lubricant) to the spark plug’s can reduce thread friction, potentially leading to over-torquing. For this reason, many experts recommend forgoing anti-seize altogether. If you feel you absolutely must use anti-seize on the plug threads, Autolite recommends reducing installation torque by 30%.

Rule-of-thumb Spark Plug Torque Chart

Without a doubt, the best method is to use a torque wrench to tighten the spark plugs to specification. But if you don’t have access to a torque wrench or torque specifications (or both), you can use the chart below as a general rule-of-thumb:

Torque Recommendations Table
If you don’t have access to a torque wrench or torque specifications (or both), you can use the chart as a general rule-of-thumb.

As you’ll notice in the chart above, the spark plug’s seat design plays a role when it comes to torque specifications. Gasket-type (flat seat) spark plugs have a gasket at the seat to seal the combustion chamber. Tapered seat spark plugs do not have a gasket, as their outer shell alone can seal the combustion chamber.

FAQ

Can you over tighten spark plugs?

Yes, you can definitely over-tighten spark plugs, sometimes with disastrous results. Overtightening can damage the spark plug’s insulator, housing, or threads. What’s more, overtightening can cause damage to the threads in the engine’s cylinder head, which can lead to a costly repair. A spark plug that’s installed too tight can also run too hot, leading to pre-ignition and detonation inside the engine, potentially causing extensive internal damage.

What happens if your spark plugs aren’t tight enough?

A spark plug that’s too loose can also be problematic. Not only can under-tightening cause damage to the spark plug, but it can also lead to pre-ignition and potential engine damage. The loose spark plug may also blow out of the spark plug hole, causing damage to the engine’s cylinder head. Performance problems, such as misfiring and an illuminated check engine light, can also result.

How do you know if a spark plug is loose?

The best way to determine if a spark plug is too loose is to turn the plug with a ratchet and dedicated spark plug socket. If the spark plug spins around effortlessly, it’s far too loose. You can also torque the spark plug to specification to ensure it’s tight enough.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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