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NGK and the "Anti Anti-Seize Letter"
October 15, 2012

B2000 Head with Broken Plub


I was recently browsing eBay and stumbled across a listing for a Mazda B2000 Cylinder Head.  As I scanned the listing, the seller revealed that the head still had a broken spark plug in it.  He even had some pictures of it. “I wonder how that happened?” I thought to myself.  “Over-torqued it?  Didn’t use anti-seize compound?  Or maybe he did when he shouldn't have!” It reminded me of a technical bulletin that NGK put out several years ago recommending against using anti-seize compound on most plugs.

    NGK Technical Bulletin

Who’d of thought that using anti-seize could result in, well, a seized spark plug?  Seemed pretty counter intuitive at first glance. It reminded me of comedian Tim Allen, who told about the time his wife yelling at him for putting dirty dishes in the dishwasher. Apparently, as she explained to him, “you have to wash them first ,“ before you put them in the dishwasher!


As it turns out, NGK went on to explain that all of their spark plugs are manufactured with a shiny special “trivalent zinc-chromate shell plating” that is designed to prevent corrosion and seizure to the cylinder head. The shell plating acts as a “lubricant” that helps the plug release from the cylinder head during removal. In fact, on aluminum heads, they recommend only using plugs with the special plating to act as a safeguard against damage to the head and plug.


But a little anti-seize couldn’t hurt, could it? Well, the problem it seems, is that using anti-seize on plugs with the shiny metal plating can cause the installer to inadvertently over-torque the plugs, by as much as 20%.


“Over-torque stretches the metal between the last thread and the seal between the cylinder head and the spark plug, causing a much higher probability that the spark plug will break during installation or removal.” 
NGK Technical Bulletin 0907-1

Ever since reading this bulletin, I have avoided using anti-seize on NGK spark plugs.  Although I've never had any trouble using anti-seize in the years prior, I figured I might as well follow the experts advice.  Here are a few more tips I picked up over the years:

  • Always use your vehicles manufacturer's recommended plug specifications
    Installing a spark plug that protrudes longer the recommend could result in interference with the cylinder - causing significant damage.  Using a hotter than recommended plug could result in pre-ignition, reduced performance, and damage to the plugs and engine.  Using a colder than recommended plug will likely result in increased plug fouling.  If you have modified your engine to increase performance, you might benefit from using a colder plug.
  • Always remove and replace spark plugs in a cold engine
    Since aluminum cylinder heads expand when heated, they can increase their grip on spark plugs and increase the chance of breaking one during removal.  Installing a spark plug in a hot engine will not yield the proper torque values.
  • Always Torque to your manufacturer's specifications
    An under torqued spark plug may rattle loose and leak.  It may also fail to adequately dissipate heat to the cylinder head; resulting in a hotter spark plug and possibly causing pre-ignition.  An over-torqued spark may seize, cause thread damage to the cylinder head or plug, or cause internal damage to the spark plug.

Additional reading on spark plugs:

NGK: 5 Things you should know about spark plugs

Cracking the Code: The NGK Part Number Legend


  NGK Spark Plugs

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