I replaced my 97 Saturn SW2's spark plugs and spark plug wires and when I did so I applied dielectric grease to the boots of the spark plug wires. However, some instructions recommend applying the dielectric grease to the ceramic of the spark plug as well. Should I do this? Why?
The purpose of the grease is to seal out moisture so that the metal contacts on the plug and in the wire do not corrode. Also, having the grease keeps out moisture that might provide a path for arcing if it were present. Basically, the more grease the better,except for one problem. The grease makes the boot slippery and on some applications the boot tends to slip off the plug because of the tapered design of he plug ceramic insulator. So, if your boots are designed to stay put even with the slippery grease on the spark plug ceramic, then you should take advantage of that and apply the grease to the whole thing. You will get better protection from the invasion of moisture under the boot. However, if you boot is just a tapered cone, applying the grease to the spark plug ceramic might cause the boot not to grab well and allow it to slip off.
Why not i.e. it protects your spark plug boots from damage caused by heat! - keeps them boots nice a soft! Also protects electrical connectors from corrosion caused by electrolytes and other corrosive crap!
Dielectric grease does three things: first of all it prevents moisture from getting onto things, secondly it seals dirt contamination out (which absorbs moisture) and third it provides some lubrication to prevent things from sticking.
In general, you can't use too much of it, except in cases where you might want things to stick a little better. The only worry is that your plug wires might not stick on the plugs as solidly if you grease the whole thing completely. That's probably a non-issue.
Don't forget to use it every time you change any connector under the hood or in the body, and always use it when you change light bulbs. It will dramatically reduce connector corrosion twenty years down the road.
No, and if anything it promotes heat conduction, but that's harmless since it makes only a trivial difference in the case of boots that already fit tightly against the spark plugs, and the silicone rubber that virtually all modern plug boots are made of is highly resistant to heat.
Only if applied to the outsides of the boots and the boots are not made of silicone rubber. Probably no spark plug boots are any more, but it's possible that some distributor boots are.
A neighbor of mine once had to change a 120-volt 60-watt light bulb that had been in its socket, and turned on, for more than 10 years. Couldn't do it! It had somehow welded itself to the socket. Grease would have prevented that.
I've seen this grease inside GM sensor connectors, but I've seen other brands that were assembled either dry or with a coating that was not obviously present or greasy. The film of dielectric grease will be pierced by the metal contacts. This is also why it's OK to coat battery terminals and cable ends with grease (dielectric or disk brake) before attaching them together.
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