Why use dielectric grease on the top ceramic insulator?
One of the normal effects of operating a high voltage electrical system (like the ignition system on your vehicle) is the formation of a “corona voltage” on the external surface of the conductor (wires or insulators). As the voltage increases (as it does when a spark plug gets older and the gap wears larger), this “corona voltage” will increase. By using dielectric grease on the top ceramic insulator and lower edge of the wire or coil boot, this corona voltage is reduced and the plug will last longer before needing replacement.
