There is a big misconception about dielectric and thermal conductive greases and the job they perform. Despite the word “electric” in its description, dielectric grease does not conduct electricity. It is, in fact, an insulator. So, it should never be used for high-tension leads like spark plug connectors. Where you should use dielectric grease is around the inside of the spark plug boot to seal out moisture and prevent the boot from sticking to the spark plug ceramic. A good example of this grease is MSD’s Spark Guard which you can find at Summit Racing under P/N: 8804 or Permatex P/N: 81150 in a 0.33-ounce tube.

Also, dielectric grease should never be used between an HEI module and the distributor body. What should be used instead is thermal transfer grease which is commonly white in color because its main component is aluminum oxide. In the HEI application, thermal grease is used to improve heat transfer between the module and the distributor body. A new module usually comes with a small tube of this heat transfer gel. But if not, this must still be used or the module may quickly fail.

The MSD grease called Spark Guard should only be used to lubricate the spark plug boots to prevent them from sticking. Never use this lube to coat the spark plug electrical terminals as this material is an electrical insulator and will reduce voltage to the spark plug.

We found a small tube of this thermal transfer grease at AutoZone under part number SL203 for less than $5.00. We also found a larger tube of Super Lube at Grainger for a decent price. There are many others but be careful because some are described as dielectric grease which may not be a thermal transfer material. It’s always a good idea to check carefully and ask questions to determine exactly what the product does.

A third material that is also often used around spark plug threads is anti-seize. The issue with anti-seize is that it is a very conductive material — the exact opposite of dielectric grease. If you must use anti-seize on spark plug threads,  use it very sparingly. We’ve seen spark plugs literally dripping with this stuff on the threads which makes it very easy to find its way to the business end of a spark plug where the spark will ground out and create a misfire. You don’t see anti-seize used on race engines for a reason, so use it sparingly on the threads.

Anti-seize should be used very sparingly with spark plug threads mainly because the grease is a highly conductive material. If any of this material comes close to the center electrode, it can cause a plug to misfire.