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  #1  
Old 04-08-2010, 12:15 PM
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Dielectric Grease on Plug wires?

All

Well I am half way through my first project on my 89 300SE (W126) with the M103 engine.

Here is the link to my previous post - Plug gap and Oil question

Got the upper timing case seal and Cam Seal changed out and I started on the Plugs, wires and cap/rotor. I pulled number 1 plug and found a Bosch H8DC in there and it had a gap of .045!. It looked pretty good but had some center electrode wear. H8 is a different heat range correct? I have the proper H9DC0 plugs I am replacing them with. (note NO R! )

So do i put any Dielectric grease on the insides of the plug wire ends? any thing in the center of the Rotor?

Any other tips are always appreciated? Working with that half broke fragile wire tray should be fun.

I have not looked at the new wires yet so if they have instructions that tell me to do so this will verify that! thanks.
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  #2  
Old 04-08-2010, 12:27 PM
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Dielectric grease does not conduct electricity. It's an electrical insulator not a conductor. It's only used for the rubber portions of the spark plug boots to keep moisture out and to keep the boot from sticking to the ceramic portion of the plug. Electrical conductors should not be coated with dielectric grease prior to being mated. A lot of people think it enhances electrical conductivity, a common misconception.
You should just ensure that the contacts are clean and you should be good. Maybe a slight film of some conductive grease if you want to feel better.
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  #3  
Old 04-08-2010, 01:59 PM
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Also dont forget the anti-seize compound on the plug threads! Steel plugs aluminum heads.............................
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Old 04-08-2010, 02:29 PM
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Dialectric grease on plug boots is a good idea. It keeps moisture from getting in, as well as it prevents the rubber from getting stuck after a while. The bosch wire set I got from here had a little pack of dielectric grease in it for the rubber boots.
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  #5  
Old 04-08-2010, 03:25 PM
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DON'T use dielectric grease on the cap or rotor contact! The contact is a spring loaded carbon brush, it's self lubricating, and it sheds a small amount of carbon dust. That carbon dust plus the grease will turn the grease conductive, and the heat and centrifugal force will make it ooze all over the inside of the cap until you start arcing over.

In other words, it will ruin your cap and rotor eventually.
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  #6  
Old 04-09-2010, 12:46 AM
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I assume you're talking the cap/rotor contact INSIDE the cap, tinypanzer?

I'd never heard of someone using the grease inside the cap at all, but I suppose anything happens given enough tries!


Outside the cap, I definitely use it, as that's the connection seeing the most energy and the most likely to be heating and oxidizing if any moisture gets to the connection.
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  #7  
Old 04-09-2010, 05:01 AM
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I'd recommend this spray-in stuff, "oxidation preventer", not dielectric grease.
Page 38 in this PDF, Wurth Contact OS, is the right stuff to use:
http://www.wurthusa.com/project/media/new_online_catalog_2010/04_Chemical.pdf

Nothing in the cap, that has a rubber seal and should stay dry, but some guys in the shop would spray the Contact OS in there.

Gilly
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  #8  
Old 04-09-2010, 12:19 PM
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Thanks for the info.

Per the instruction sheet for the Bosch wires I put grease on the rubber parts of the boots only and very sparingly. Nothing in the cap and rotor area. I also put a new seal on the distributor cap as the old one was hard. The car does run and start much better now. It felt like it needed a "tune up". So i have new plugs, wires, cap, rotor, cap gasket. I also changed the engine oil/filter on it (really need a different filter wrench).

So all is good now.

I do have a very intermittent Stalling issue when decelerating to a stop. it just won't catch idle at times. Been searching the boards on that one. Other than the stall and the need for a brake job soon its doing well!
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  #9  
Old 04-09-2010, 01:48 PM
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I always use a product similar to the one that Gilly showed. It is electrical contact cleaner. I like to use it to remove excess carbon and rotor tracking debris between tune ups. All of that debris in the cap is mostly conductive and can cause arcing in the cap
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  #10  
Old 04-09-2010, 07:28 PM
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This stuff is a oxidation "prevention" is what it says on the can. I always say "a can of oxidation prevention is worth a pound of oxidation cure!". The "OL" was the cleaner, they have cleaner and they had preventative.
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Old 04-09-2010, 07:28 PM
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