Where/How to apply dielectric grease?

[SavagePatch]

I tried the search function and didn't find the answer I was looking for.

I've always just put a small amount of dielectric grease on the ceramic part of the plug and a small amount on the inside of the boot that comes in contact with the ceramic. Is this correct? Is there even a definitve answer or is there a few different camps of thinking like most topics?

Also, what brands do people like/recommend? I've always just bought a "ketchup" packet at the checkout counter.

Thanks in advance!

 

[zrxkawboy]

Yes, that sounds like a good plan. I just use the small tubes of Permatex, but I'm sure any brand is fine.

 

[demarpaint]

That's what I do. It makes removing the wire a lot easier when it comes time to change the plugs.

 

[BigD1]

I put a good dab on the end of a flat blade screw driver, and put it right on the inside of the boot at the tip. Then when the boot slides over the spark plug, the plug and inside of the boot both get a good coating plus makes a good seal against moisture.

 

[DBMaster]

Originally Posted By: BigD1
I put a good dab on the end of a flat blade screw driver, and put it right on the inside of the boot at the tip. Then when the boot slides over the spark plug, the plug and inside of the boot both get a good coating plus makes a good seal against moisture.


+1

 

[Leo99]

Hmmm, I put a small dab on the terminal end of the sparkplug.

 

[andyd]

Originally Posted By: demarpaint
That's what I do. It makes removing the wire a lot easier when it comes time to change the plugs.
I had no trouble removing the wires. Trouble was, they came off, leaving leaving the terminal and the boot on the plug. I had a set of wires on an old Willys. In damp weather, it was hard to start. I bought a tube of di-electric grease and massaged it into the wires. Fixed.I make sure I have some around for plug jobs.

 

[mclasser]

I squeeze some into plug wire boots and the contact points on the end of distributor caps. Saw a Scotty Kilmer video where he advocated using it on wiring harnesses/connectors as well.

 

[Gasbuggy]

Buy a large tube. It does not expire. I run a fat bead across the opening of the spark plug and then stick it on. It's better that way, helps the boot not bond to the plug when you pull them off years later.

 

[BigD1]

I have an eight ounce container of the 3M silicone paste, so that's why I use a flat blade screw driver to apply it to the inside tip of the boot.

 

[Blueskies123]

I believe this incorrect. The grease will interfere with the electrical current. It should just be on the boot not on the terminal end of the sparkplug.

 

[AZjeff]

Interestingly dielectric grease is non-conductive. The reason it works on spark plugs and dizzy caps is the pressure at the point of contact forces it away. It then seals the contact point. Not supposed to use it where there's a chance of arcing.

Bluesky, if the plug wire connectors aren't a tight fit it could restrict current.

 

[spackard]

You are supposed to put it on the metal plug terminal nut, to displace any air when the plug wire is put back on. No air, no arcing and oxidation of the metal if the fit isn't quite right.

I like a little on the ceramic too because it makes it easier to take apart years from now.

 

[kschachn]

Originally Posted By: AZjeff
Interestingly dielectric grease is non-conductive. The reason it works on spark plugs and dizzy caps is the pressure at the point of contact forces it away. It then seals the contact point. Not supposed to use it where there's a chance of arcing.

Bluesky, if the plug wire connectors aren't a tight fit it could restrict current.


This is correct. If there isn't a tight fit then there will be restricted conductivity, grease or no grease. This question come up a lot when dielectric grease is discussed, but numerous studies (including the military) are available for reading online that show there is no degradation of conductivity when the grease is used.

Next someone usually brings up conductive grease which is the last thing you want in this type of application. Conductive greases are used to conduct heat, not electricity. In electrical connections you never want the current to have to flow anywhere except through a terminal-to-terminal connection.

 

[Scott_Tucker]

As someone who has been in the business for 30 years and specializes in old cars, this is incorrect. The grease should only be used on the boot to help seal out moisture and prevent sticking. Dielectric grease is non-conductive and I have seen it cause misfires many times when it is slobbed onto the terminal of a spark plug.

 

[kschachn]

The dielectric strength or breakdown voltage of the silicone dielectric grease is higher than that of air (which is what you would have without it). It is non-conductive, yes. That's what you want. You never want the current to flow through the insulator, only the terminal. Besides, silicone greases are notorious for migration. If you are putting it on the boot it is going end up on the terminals too.

I'll also say it does no real good to have it on the terminal either unless the boot degraded. Using dielectric grease in a spark plug boot is just to make the boot release from the ceramic as has been said. There shouldn't be any water getting inside that boot when installed, so the terminals shouldn't be corroding.

 

[Bamaro]

Originally Posted By: Scott_Tucker
As someone who has been in the business for 30 years and specializes in old cars, this is incorrect. The grease should only be used on the boot to help seal out moisture and prevent sticking. Dielectric grease is non-conductive and I have seen it cause misfires many times when it is slobbed onto the terminal of a spark plug.

Yup, its an insulator, not a conductor.

 

[SOHCman]

Originally Posted By: Bamaro
Originally Posted By: Scott_Tucker
As someone who has been in the business for 30 years and specializes in old cars, this is incorrect. The grease should only be used on the boot to help seal out moisture and prevent sticking. Dielectric grease is non-conductive and I have seen it cause misfires many times when it is slobbed onto the terminal of a spark plug.

Yup, its an insulator, not a conductor.


I could see this being an issue on old style wire boots, or perhaps inferior/cheap boots that don't positively snap over the end of the spark plug, but I have never had misfire as a result of dielectric grease in the boot or on the tip of the spark plug, and I slather that stuff on practically filling the boot!

When I go to change the plugs years later, you can plainly see where the connector in the boot made positive contact through the grease by displacing it. Same deal on the coil-on-plug in one of the cars.

I'm not saying it can't happen (especially with inferior parts) but no issues here. The only time I have EVER had a stuck boot is when changing plugs on a "new to me" vehicle and you can tell the PO skimped on the grease.