There seems to be a lot of conflicting answers on what you're supposed to do with dielectric grease. The instructions on the grease I bought says to squeeze it into the boot, but everywhere I've read online says to only put a TINY bit on the porcelain since it's non-conductive.

I squeezed a decent amount of dielectric grease into my spark plug boots and now I am wondering if it could have an effect on the ignition.

Is there a definitive answer on what you're actually supposed to do with dielectric grease?


tl dr: You've hurt nothing by putting more than a little bit of grease in the boot ... don't worry about it.

Dielectric grease serves two purposes:

  • Prevent electrical leakage
  • Keep the boot from sticking to the porcelain of the spark plug

According to Wikipedia:

Dielectric grease is electrically insulating and does not break down when high voltage is applied. It is often applied to electrical connectors, particularly those containing rubber gaskets, as a means of lubricating and sealing rubber portions of the connector without arcing.

It's specific design is to help ensure arcing does not occur. It also helps keep water/moisture out of the boot as well, which can cause electrical leakage and ultimately arcing. Remember that direct current (what we find in cars) will find the easiest route to ground. Ignition voltage ranging around 40k-50k vdc can be considered high voltage. Putting the extra grease in the boot has only made it so you shouldn't have either of the issues which dielectric grease is meant to prevent. If it squishes out from the boot as you push it on, you've probably used too much. A little dab may only prevent the boot from sticking, but will it actually prevent electrical leakage? Probably not.

  • TERRIBLE answer! Dielectric grease is an INSULATOR and will cause misfiring if applied to any electrical connection-it is great for the boot and can be sparingly apprised to the boot youtube.com/watch?v=-542IYGBbpg – Bill Hoidas Sep 14 '18 at 23:59
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    @BillHoidas - Welcome to Motor Vehicle Maintenance & Repair! How does what I wrote disagree with what you've said? They are pretty much lock step. Also, please take the Tour, as this will help you understand how Stack Exchange works and functions. – Pᴀᴜʟsᴛᴇʀ2 Sep 15 '18 at 12:21

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