Where to put dielectric grease on spark plugs? How to clean plug chamber...

[golden1245]

Hey guys, I'm replacing the spark plugs on my '99 C230K today with some NGKs.

I know that i'm suppose to a tiny bit of anti-seize on the threads, but I also read on the American forums that I'm suppose to "clean up" the inside of the spark plug chamber with a little bit of dielectric grease?

This is what the inside of the chamber looks like...there's a bit of yellowing at the very end, not sure if that's oil.

Am I suppose to stick a lint-free rag down there and try to clean it up or should I just leave it? Besides doing that, i read that I'm suppose to put a very tiny bit of the dielectric grease on the tip of the spark plug boot...which i'm confused about. Do I put it on the ceramic part or in the spark plug wire boot? Or is dielectric grease not even necessary?

These are how my old spark plug looks at the moment next to the new ones, they have about 53,000 miles on them. Judging from the color, it looks like the engine is pretty healthy I'd say.

 

[grober]

My guess is that they are recommending the application of the dielectric grease to prevent the the spark plug connector from sticking to the plug insulator or the walls of the plug recess and possibly prevent the ingress of moisture.
see Wikipedia
Dielectric grease

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.

A common use of dielectric grease is in high-voltage connections associated with gasoline engine spark plugs. The grease is applied to the rubber boot of the plug wire. This helps the rubber boot slide onto the ceramic insulator of the plug. The grease also acts to seal the rubber boot, while at the same time preventing the rubber from becoming stuck to the ceramic. Generally spark plugs are located in areas of high temperature, and the grease is formulated to withstand the temperature range expected. It can be applied to the actual contact as well, because the contact pressure is sufficient to penetrate the grease. Doing so on such high pressure contact surfaces has the advantage of sealing the contact area against corrosion.

Another common use of dielectric grease is on the rubber mating surfaces or gaskets of multi-pin electrical connectors used in automotive and marine engines. The grease again acts as a lubricant and a sealant on the nonconductive mating surfaces of the connector. It is not recommended to be applied to the actual electrical conductive contacts of the connector because it could interfere with the electrical signals passing through the connector in cases where the contact pressure is very low. Products designed as electronic connector lubricants, on the other hand, should be applied to such connector contacts and can dramatically extend their useful life. Polyphenyl Ether, rather than silicone grease, is the active ingredient in some such connector lubricants.

Probably unnecessary to be honest-- certainly on the plug recess itself. Secret with this type of lubrication is not to overdo it- you are looking only to coat any surfaces with a very thin film of grease. Often best achieved by merely wiping the plug upper body with a cloth with some grease absorbed on it. Such that it feels "greasy to the touch" without great "gobs of grease" -- on it. The jury is out on anti seize compound on plug threads- some advocate it some don't. If you do use it use it sparingly!! and use a top quality anti seize compound and use a low range torque wrench to tighten the plug to the recommended torque !
ps:- glad to see you are moving to the iridium fine tip electrode plugs

 

[golden1245]

thank you very much Grober...but it seems like i've run into another big problem...please see different newer post.