Rick's Free Auto Repair Advice

Anti-seize on spark plug threads

Should you apply anti-seize on spark plug threads?

Generally the answer is No. But there are a few exceptions.

If the spark plug threads have a chrome plated look or are shiny, they’ve been treated with an anti-seize coating at the factory. Do NOT apply anti-seize to these spark plugs.

anti-seize on spark plug threads

This spark plug does not need anti-seize and you should NOT apply it.

anti-seize on spark plug threads

If the spark plug has a black oxide finish, it has NOT been coated at the factory and you should apply a very small amount of anti-seize to the threads

Here’s why applying anti-seize can actually screw things up.

In the OLD DAYS, Copper spark plugs never needed anti-seize

In the old days when engines and cylinder heads were made from cast iron and copper spark plugs only lasted 12,000 miles, there was no need for anti-seize. The spark plugs never stayed in the engine long enough to seize to the cylinder head. Plus, they were similar materials—steel and cast iron.

Platinum spark plugs and aluminum heads changed everything

When car makers switched to platinum tipped spark plugs that lasted up to 100,000 miles, spark plugs started to seize in the cylinder heads. The problem got even worse as car makers switched to aluminum cylinder heads. The dissimilar metals went through a galvanic reaction where metal transferred and welded the spark plugs to the head. When the DIYer or professional tech went to remove the spark plugs, they would often rip the threads right out of the cylinder head.

That’s when spark plug manufacturers and car makers started recommending the application of a small dab of anti-seize on spark plug threads. That way, the spark plug could be removed easily the next time.

Why has anti-seize been eliminated?

Car makers met with the spark plug manufacturers to find a better solution. The problem with anti-seize is two-fold. First, the torque specs for spark plugs going into an aluminum head is pretty low; sometimes as little as 10-12 ft/lbs. If you over tighten the plug, you risk, distorting the shell which breaks the seal between the shell and the porcelain. That causes a leak of combustion gasses. Over tightening can also damage or rip out the threads in the cylinder head, causing far greater damage. On the flip side, under-tightening can cause the spark plug to blow out, taking the cylinder head threads with it.

Adding anti-seize on spark plug threads causes over torquing

Spark plug torque specs are based on DRY threads. When you apply anti-seize, you must reduce torque by 10-15%. Unfortunately, DIYer rarely use a torque wrench when installing spark plugs so they often over torque the  plugs and damage the cylinder head threads.

Spark plugs manufacturers now apply plated anti-seize on spark plug threads

To eliminate the problems associated with spark plugs seizing to the cylinder head, most spark plug manufacturers now apply a metal plating to the threads of new spark plugs. The coating is good for a single installation. If you remove the spark plug and reinstall it, you must apply anti-seize during the re-installation.

However, there’s a caveat; spark plugs that have a blackened or dull appearance don’t have this metal coating, so they require anti-seize.

How much anti-seize should you apply?

If you’re RE-INSTALLING spark plugs, you should apply anti-seize because the factory applied release agents are damaged upon removal. Most

too much anti-seize on spark plug threads

Whoa dude, that’s WAY TOO much anti-seize

DIYers add WAY too much anti-seize. More is NOT better. The excess anti-seize can transfer to the electrodes, causing misfire. The excess anti-seize causes over tightening and spark plug

anti-seize on spark plug threads

Add a tiny amount a few threads down from the tip to avoid tip contamination

shell distortion and combustion gas leaks and also spark plug thread damage in the cylinder head.

Here’s what the spark plug manufacturers say about anti-seize

excessive anti-seize on spark plug threads

Too much

NGK’s position on anti-seize

NGK spark plugs are manufactured with a trivalent plating. The spark plugs display a silver or chrome finish on the threads. The trivalent plating reduces corrosion resistance from moisture and chemicals.  The trivalent coating also acts as a release agent during spark plug removal. NGK spark plugs should be installed DRY, WITHOUT anti-seize.

NGK reports that tech support personnel have received a number of calls from installers who have over-tightened spark plugs because of the use of anti-seize. Anti-seize is a lubricant and affects torque values by up to 20 percent. If you use anti-seize against NGK recommendations, you MUST decrease the set torque on your torque wrench by that amount or risk breaking the spark plug, distorting the shell, or damaging cylinder head spark plug threads.

Autolite’s position on anti-seize

Autolite does NOT recommend the use any type of anti seize lubricant when installing new Autolite spark plugs. Since anti-seize compounds contain metallic, electrically conductive ingredients, the ingredients can come in contact with the electrodes on the spark plugs, leading to misfires. Anti seize lubricants also introduce a torque multiplying effect, leading to cylinder head spark plug thread distortion, galling and cylinder head damage.

Autolite applies a nickel plating to the threads of new spark plugs that resists corrosion and seizing.

AC/Delco’s position on anti-seize

AC spark plugs should be installed dry. Do NOT use any type of anti-seize lubricant on spark plug threads. Anti-seize lubricants decrease the amount of friction between the threads, resulting in over tightening. That can cause the spark plug to move too far into the combustion chamber (in crush washer applications). Over-tightening can also distort the spark plug shell, causing a leak which would allow blowby to pass through the gasket seal between the shell and insulator. Over-tightening also results in extremely difficult removal.

Champion spark plug position on anti-seize

Champion spark plugs are zinc plated to reduce the chance of seizure in aluminum cylinder heads. Champion then applies Tin Tac” and ULTRASEAL’M coatings over the plating to further reduce corrosion and seizure. Anti-seize should NOT be applied to new Champion spark plugs.


Posted on by Rick Muscoplat

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