Repair 7

Do You Need Spark Plug Lubricant

Some roads are paved with good intentions, others with broken dreams; still others are paved with broken down cars, formerly driven by people with good intentions. Lubricating spark plug threads is one of those things that seems like a good idea at the time, until you realize all the reasons that you shouldnt do it.

Spark Plug Basics

A spark plug is, in essence, the end and the weakest link in a long circuit. The electrons flowing across the gap from the spark plug tip to the ground strap start at the battery. Electrons flow from the battery, and through the ignition coil where they induce a high-voltage/low-amperage in a metal core. The high-voltage electricity flows through that core and into the plug wire -- or spark plug, if its direct ignition -- where it flows down the plugs central, metal core. From there, the electrons jump the gap in the form of a spark to the ground strap, grounded to the battery via the cylinder head and ground strap.

A Case for Lube

Anti-seize lubricants are usually some mixture of soft metals with high lubricity -- copper and aluminum, typically. They also generally contain some amount of graphite, which acts as a "dry" lubricant and helps to keep bolt threads from sticking to the threads of a bolt hole. Antiseize lubricants do their best work on bolts in high-temperature, mixed-media applications -- steel bolts into aluminum heads, chrome-moly exhaust manifold bolts into iron heads and so on. Anti-seize lubes can go a long way toward the prevention of stuck bolts, stripped threads, stripped bolt heads and broken spark plugs.

Electrical Conductivity

Contrary to popular belief, most anti-seize lubricants are fairly good conductors of electricity -- they just need to get hot to do it. Aluminum and copper are two of the best electrical conductors on Earth, and graphite is a fine conductor as well. But, unlike most materials, this crystalline form of coal has whats called a "negative coefficient of resistance," meaning that it works better when its hot. Very hot -- about 900 degrees Fahrenheit. So your ignition system wont work very well at startup or unless the engine runs consistently at very high temperatures. Thats why its often proscribed for use in aircraft engines, which require regular maintenance and run at high loads for hours at a time.

Galled Threads

Not all antiseize compounds contain graphite; some specialized compounds designed for use with electrical components contain nothing but copper, aluminum, nickel and other conductive elements. But that still does change the fact that antiseize lubricants are still lubricants, and that theyll reduce required torque by about 20 percent. Which means that, when you use an antiseize lube and torque the plugs to the factory setting, youre actually over-torquing by about 20 percent. When dealing with aluminum heads, an extra 20 percent is easily enough to rip the threads right out of your head, thus creating the very problem you were trying to avoid.