How to Change Your Spark Plugs & Why You Shouldn’t Use Copper Grease

How to Change Your Spark Plugs & Why You Shouldn’t Use Copper Grease

Should You Use Copper Grease/Slip/Anti-Seize on Spark Plug Threads?

The question of spark plug changes is frequently asked online, and we aim to provide a clear answer. Some offline stores may exploit this topic to promote their copper grease products, but we delve deeper to uncover the truth. So, what is the accurate information and what misconceptions exist?

The Correct Answer

Virtually all spark plugs now feature a special anti-seizure nickel or zinc-chromate shell plating. Basically, you can think of the plating as a replacement of thread compound or copper slip.

Here’s what NGK says:

NGK spark plugs feature what is known as ‘trivalent plating’. This is a silver-or-chrome coloured finish on the threads that is designed to provide corrosion resistance against moisture, chemicals and weathering. The coating also acts as a release agent during spark plug removal.

NGK spark plugs are installed at the factory dry, without the use of anti-seize. NGK tech support has received a number of tech calls from installers who have over-tightened spark plugs because of the use of anti-seize. Anti-seize compound can act as a lubricant altering torque values up to 20 percent, increasing the risk of spark plug thread breakage.

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Why Do Torque Values Change With Copper Slip?

Because there is less friction between the two materials, more force can be applied to the plug’s preload. The preload is the ‘tension’ between the spark plug and cylinder head thread which stops them from coming loose.

You will end up over-tightening them by up to 20% which is easy enough to break them if using an anti-seizure agent. This goes for anything and everything to do with torque wrenches, always use torque specifications ‘dry’ unless stated otherwise.

In Our Experience

For NGK warranty purposes, we send all damaged spark plugs back to NGK UK so that they can be officially examined and documented. As of now, it turns out 100% of the spark plugs in the last 5 years that were returned due to thread breakage were the result of customers using thread compound, or simply over-tightening them.

The NGK warranty reports are always compiled with detailed (and sometimes magnified) photographs pinpointing the exact reasons for failure, even to the very smallest of details such as hex swelling. So they know what they’re doing!


My Mechanic Always Uses Copper Slip on Spark Plugs?

If your mechanic uses copper grease on spark plug threads, as well as torquing them down; then be warned!

NGK is adamant this procedure should be avoided at all costs. We must remember that spark plug manufacturers are the most experienced out of all of us, with millions of pounds spent on R&D and hundreds of technicians logging spark plugs through stringest tests.

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NGK Tech Bulletin

NGK released an official tech bulletin to all suppliers about the issue with copper slip.


The Definitive Spark Plug Installation Guide

1. Before even buying new spark plugs, go to and verify which NGK part number are the correct ones. This will also show you what sized spark plug socket you’ll need by looking at the plugs specification and finding ‘hex’. You will need a spark plug socket to change your spark plugs. The part number shown in the results will be come pre-gapped correctly unless the part finder states otherwise.

2. Remove any top engine covers and locate the spark plug ignition coils/HT lead or spark plug covers and remove them by carefully pulling upwards, if they’re coil-on-plug type they may have a bolt holding them in place. Then lay them out on a piece of clean rag in the same position that they’ve been removed – 1, 2, 3, 4 etc.

3. Before removing the spark plugs, blow away any debris from the plugs recessed area using compressed air (or a can of compressed air) if available.

4. As mentioned, use to lookup the existing spark plugs hex size, so that you can fit the correct sized spark plug socket. This is found in the part finders search results, then click ‘view’ to view the plugs specification.

5. Ensure you are using a ‘spark plug socket‘ which helps stop a phenomon known as ‘socket strike‘ – see our article here. Spark plug sockets also grab onto the plug so you can pull them out, some use a rubber grommet while others use a sprung clasp system.

6. Connect an extension if needed to the socket and then carefully push down the spark plug socket while turning carefully to engage into the spark plugs hex. From here on, it is essential that the socket and extension must not bend/skew off angle, otherwise socket strike can occur as previously mentioned.

7. Top tip – Some spark plugs are fitted with a crush washer which can become seized/stuck onto the cylinder head, even though the spark plug is able to be unscrewed. When this occurs, unscrewing the spark plugs can feel pretty tight because the washer on the plug is being pulled through the spark plugs threads which it is not designed to do.

The washer may eventually work free of the cylinder head or may simply unscrew out of the plug completely. If you’ve removed the plugs and the gasket is still stuck on the engine head, use blue roll rag to block the plug hole and then use a long dental pick to loosen off the washer.

8. After removing the old spark plugs, check the condition and cleanliness of the cylinder head threads, if they’re really dirty and oily then this can lead to inaccurate torque wrench readings when installing the new plugs. It is paramount that care must be taken so that no debris falls into the cylinders. Spray some brake cleaner onto a clean rag/kitchen roll and wipe them over the threads to remove any grease or dirt. Alternatively, you can use a spark plug thread chaser.

9. Ensure the plug is gapped according to the vehicle manufacturer’s specifications. Multi-ground electrodes and precious metal plugs (iridium, platinum tip etc) should not be re-gapped due to the risk of damaging the fine tips. If you used the website and purchased the plug according to what the results gave, the gap should already be correct unless the part finder states to alter it.

To check the gap on multi-ground spark plugs you can use a fine wire type gauge.

10. Warning – Do NOT apply copper grease/slip or anti-seize to the new spark plug threads, copper grease is only to be used on classic black spark plugs which don’t feature a corrosion-resistant zinc plating.

11. Install new spark plugs and finger-tighten them until they stop – A length of rubber tubing pushed over the insulator is a useful aid for plug installation where access is difficult.

12. If you have a torque wrench, then tighten the plugs to the specified torque setting in the table below. Make sure your torque wrench has the correct load ranges and that it has a calibration certificate, spark plug torque settings are reasonably low so a smaller wrench will be necessary.

Note the following:

NGK does not recommend the application of lubricant such as copper grease to spark plug threads as the result is a reduction of frictional forces at the thread faces. This will render the torque readings inaccurate and over-tightening could occur by up to 20 per cent!

It’s very important not to over or under-tighten spark plugs during installation. Over-tightening can lead to distortion of the spark plug and breakage. Under-tightening can cause overheating due to poor heat dissipation and in extreme cases can cause spark plug breakage and/or major engine damage.


13. If you don’t have a torque wrench, finger-tighten the plugs and then follow the guide below, or follow the guide on the box the plug comes in. NGK usually provides t

spark installation

14. If your engine has the more modern ‘COP’ system (coil-on-plug) then lube the spark plug boot of the coil with dielectric grease, this helps prevent misfires and makes removing easier in the future.

15. Refit all parts in the opposite order of removal

16. Start up the engine and check for any misfires. If there are none, then you’re all good!