What Size Torque Wrench for Spark Plugs do You Need?

As a mechanic, you may need a torque wrench if you are carrying out engine repairs like changing spark plugs, gaskets, etc. The torque wrench eliminates guesswork, ensuring you don’t over or under-tighten nuts and bolts. 

what size torque wrench for spark plugs

However, while this is important, getting the right size is most important as it allows you to apply only the correct torque to any fastener. This way, unnecessary damage due to over or under-tightening is avoided. So those who intend to change their spark plugs may ask, what size torque wrench for spark plugs do I need? Let’s find out.

Why is the right torque important?

Before discussing sizes, it’s essential to understand why the right torque is significant when installing spark plugs. The incorrect torque can either cause the spark plug to be too loose, resulting in a loss of compression and power, or too tight, potentially leading to stripped threads or broken spark plugs.

The right torque ensures that the spark plug is seated correctly, facilitating optimal combustion and thereby promoting engine efficiency and longevity. Now, to attain the right torque, having the correct size of the torque wrench is fundamental.

What size torque wrench for spark plugs

Torque wrench comes in various sizes, so not all will allow you to apply proper torque to your spark plugs. Understand that using the wrong size torque wrench could damage the spark plugs and cause other engine issues. Basically, the popular torque wrenches sizes include ⅜, ¼, ½, and ¾ -1 inch torque wrenches. 

The most commonly used torque wrench for most of the vehicles is the ⅜ inch and ½ inch torque wrench. However, the exact size you need depends on your vehicle. Check your owner’s manual for manufacturer recommendations or requests online from auto supply shops.

That said, aside from the size of spark plug torque wrench, you must also consider the type of torque that corresponds to your situation. If this looks like a big deal, your auto supply shop can help with the right one for your make and model.

What happens if you do not torque spark plugs properly? 

While tightening spark plugs with a torque wrench helps eliminate guesswork, not torquing spark plugs correctly may cause issues. This is true, mainly when you use an incorrect-size wrench. 

If the spark plugs are not correctly tightened (loose), the plug will not sit fully on the cylinder head. With the plugs not installed well in the hole, the engine will eventually blow the spark out of the engine, taking the threads with them. And in the process damage the engine.

The plugs not fully seated in the engine can also slow heat dissipation which can cause the firing edge of the plug to overheat, eventually leading to misfires. Under-tightening spark plugs can also damage the plug and plug thread in the heads. Undertightening spark plugs can also result in compression leaks and damage the head if the leak worsens.

On the other hand, over-tightening the spark plugs will also rip out the thread or break the spark plugs. In summary, not applying the proper torque for spark plugs can lead to engine damage necessitating costly repairs. The best way to avoid this is to use only the correct size torque wrench and torque accordingly.

But how do you know if you’ve tightened the spark plugs incorrectly? Inspect the spark plugs yourself by twisting them. If you turn it effortlessly, they are loose. And if you can’t rotate them even with a torque wrench, they are too tight.

Proper Torque for Spark Plugs You Tube

How to torque spark plugs 

Torquing spark plugs is simple and relatively easy but could be a problem if done incorrectly. So here is how to tighten your spark correctly. But first, ensure you’re using the correct spark plug size for your engine. Secondly, get the proper torque wrench size for spark plugs. 

  • Remove dirt from the cylinder head and spark plug thread
  • Push in the spark plug into its hole and hand tight until it seats or the gasket touches the cylinder head
  • Then use a torque wrench to tighten it to the manufacturer’s specifications 

How much torque needs to tighten spark plugs?

The spark plug tightening torque needed depends on your application, plug type, and size. Before now, cylinder heads made of iron could be hand-tightened till they were seated correctly, then turned with a torqued wrench until tightened

However, cylinder heads now feature aluminum, so the same process used for iron heads may not suffice in getting the proper spark plug torque. Here, the spark plug supported by your vehicle, the thread size, and the spark plug material plays a huge role. Since it’s not a one size fit all thing, the best is to use the correct size torque wrench and follow your manufacturer recommended torque spec for spark plugs. 

How to tighten spark plug without a torque wrench

While tightening spark plugs with a torque wrench makes the job easier and torquing accurate, you can also do it without a torque wrench. Here, a spark plug wrench may suffice. To do this,

  • Remove dirt from the cylinder head  and spark plug thread
  • Put the spark plug into its hole and hand tight until it seats appropriately or the gasket touches the cylinder head 
  • Tighten the spark plug more with the wrench to your manufacturer’s specifications. 

Please note that the amount of torque needed when using a torque wrench differs from when not using a torque wrench. This should be stated in your owner’s manual.

One more thing, whether using a torque wrench or not, those manufacturer-recommended numbers of turns are only for new spark plugs. 

So if you’re dealing with old plugs, you will need to estimate the torque setting for spark plugs when hand tightening. If you follow the exact turns recommended, you may break the plugs since they are already old. 

Can you over-tighten spark plugs?

Yes, you can mistakenly over-tighten spark plugs. However, doing this will cause problems for your engines. An over-tightened spark plug can damage the hole of the cylinder head bolts. With this hole damaged, installing new plugs will be almost impossible, resulting in expensive repairs.

Over-tightening spark plugs can also stretch their metallic shell, causing the thread to break or crack. The plug’s metallic shell stretching could also break the internal gas seals or damage the insulator. Too much tight plug can cause its plug thread to stripe off. 

Fixing a plug thread will require replacing the head—an expensive repair you don’t want to do. Other possible issues from over-tightened spark plugs include a reduction in RPM, unexpected engine misfire, and engine starting issues.

Can over-torquing spark plugs cause misfires?

Excessively torquing spark plugs can cause misfires. When spark plugs are over-torqued, they can damage the insulator. This crack in the insulator can cause the spark to jump to the ground instead of going into the electrode (tip). 

With the spark missing its direction, the plug tip won’t get hot; without it, the fuel-air mixture cannot be ignited. This eventually results in engine misfires during acceleration and, other times, rough idling. So, you must know what torque for spark plugs is needed, so you torque correctly.

torque wrench for spark plugs


Anyone who intends torquing their spark plug should know what size torque wrench for spark plugs to use. This helps prevent over and under-tightening plugs which may invariably cause performance issues and engine damage. Generally, what size torque wrench you need depends on your manufacturer’s recommendations. However, the most commonly used are the ⅜ and ½ inch torque wrenches.

Before installing spark plugs, the spark holes should be cleaned. Otherwise, you may be twisting the plug against dirt, invariably preventing plugs from properly seating. So while you may be using the correct size torque wrench, your spark plug may be under-torque. Lastly, ensure you install plugs only on a cool engine because metal can expand or damage the thread.


Mr. Shafiqule Islam is a graduated Mechanical Engineer and has more than 15 years experience of repairing and maintenance of different brand vehicles like Toyota, Mitsubishi, Ford, Mercedes, BMW etc. He is also giving training to Mechanics. He has started writing to share his practical knowledge to Vehicle Owners, Drivers and Mechanics to keep their cars at best fit.

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