skpyle

Hello Gentlemen,

I am slowly working on getting the Red Witch back on the road, and am planning on a full ignition system refresh in the very near future.

I have read several threads on replacement of the spark plug wires. In none of them have I seen mentioned using dielectric grease on the spark plug boots and distributor cap ends. I ask because I am used to doing that on all my other vehicles.

Is there a specific reason why I should not use dielectric grease on the plug wire boots and ends of a 32V 928 engine?


Thanks!

Seth K. Pyle

huskeric

after accidently pulling off too many boots (meaning, the boot separates from the lead), I use a dab of DE grease on all my wires...

Chris Lockhart

Definitely use it Seth. It will make your life much easier in the future.

linderpat

I would never use dielectric grease on those connections - it is non-conductive, and can adversely affect the car's performance. Dielectric grease is used in places to coat and protect an electrical connection after it has been made - like at a ground point in the engine bay that may be subject to the elements. You would clean the connection points nice and shiney, make the connection nice and tight, then add the grease to protect it from outside elements. You would never use it for interior connections (like the pod or CE panel) since they are not exposed to the elements. Likewise, with spark plugs, the boots keep them protected at both ends - on the engine side and at the distributor cap side. Using dielectric grease as a lubricant is a bad idea in my view, since it can result in less current flowing through those points.

Eplebnista

I believe we are discussing using a little grease on the boots themselves so the ends don't weld themselves to the porcelain insulator of the plugs. I use NAPA silicone brake grease on the boot ends. Takes high temps and has never caused any problems.

928S MN

Hi Seth,

This late spring I completed a complete upper refresh on the 85. Used the dielectric grease on all the spark plug wires as well as the coil wires. As part of that upper refresh I went will all new Beru wire set, coil wires, distributor and rotors. She's running like a dream right now!

dr bob

Good for the boots on the high-voltage connections. Keep it away from the terminals themselves and you will be good. There's nothing magic about the 928 hi-tension ignition. Use the same techniques and materials as you would on any other car when it comes to this system.

skpyle

Excellent, this makes me feel better.

Point of dielectric grease in my world for plug wires is to keep the boots from sticking to the spark plug insulators and keep the caps from sticking to the distributor cap bosses.

Thank you for the confirmation.

Onward and upward!

Seth K. Pyle

P.S.: 928 MN, for the ignition refresh, I am doing the following:
-new Bosch copper spark plugs
-new plug wires supplied by Roger (Beru set for S3 NLA)
-new plug wire separators
-new Bosch distributor caps and rotors
-new Bosch ignition coils
-new Porsche ignition coil covers
-new Porsche ignition coil ground wires
-new Bosch ignition modules

The Red Witch ran fine when I took her off the road, I want to keep it that way.

linderpat

Aha! Yes, that application does make sense. I thought that it was to be used on the electrical contact itself.

928S MN

Hi Seth,

I'm definitely still learning a lot about the 928. You said you will be installing a "Bosche Ignition Module"? I honestly don't remember running across that item. Is this something that is on the 86.5 MY and not on the 85 MY that I have?

Thanks,

Paul

hacker-pschorr

No....never, except maybe on a boat trailer.

Dielectric grease on electrical connections is a great way to trap moisture and accelerate corrosion.

dr bob

Some folks promote using it while assembling low-voltage connections purely as a protectant. It's fine for this duty, but must be used on a clean already mechanically and electrically secure connection only. The claim to fame is that the grease has a high dielectric strength, so electricity doesn't pass through it. That high dielectric strength is important on high-voltage connections where metal in the grease would provide an easy arc path. So it's good for the spark plug boots, as Seth asks. Unless you need to keep moisture out of the boots (not an issue with the 928), you could do at least as well with a good silicone spray lubricant that doesn't run out when it gets hot, as most dielectric greases do.

If you want to protect ground connections or battery terminals, use Vaseline instead of dielectric grease. Again, only on connections that are already mechanically end electrically secure (clean and tightened). Vaseline has the advantage that it washes out of clothes, plus it's a lot cheaper. And it doesn't have that annoying high dielectric strength, something you don't want to have in an electrical battery or ground connection.

----

I get to do some interesting work with electric utilities, usually on the generation side. The transmission and distribution (T&D) guys manage the switchyards, and keep the high-voltage insulators clean using a high-pressure spray of de-inonized water on live circuits. One utility experimented with coating the insulators with dielectric grease, but it quickly turned to disaster when dirt accumulated on top of the grease. That dirt and contamination provided an arc path to ground of course, in spite of the dielectric strength of the grease itself. Plus it didn't wash off with DI water, so that section of the yard needed to be isolated so the insulators could be scrubbed by hand. I'd be happier putting a good coat of car wax/sealant on the insulators so the crud washes off more easily.... Might work well for spark plug boots, methinks.

skpyle

Good points, gentlemen, thanks!

dr bob: hmmmm...


928 MN: To my knowledge, the 1985 twin dizzy 16v Euro, and all subsequent 32V 928 engines had two ignition control modules mounted under a black plastic cover in front of the radiator, on the driver's side. Each module tells its coil when to fire based on signals from the EZF(K?) spark ECU.
PET refers to them as 'ignition control switch'.
The modules on the Red Witch are 30 years old, and can fail.
I am updating everything with the eye of making my 928S a daily driver.


Seth K. Pyle

hacker-pschorr

They are often refereed to as ignition amplifiers.

They do fail, but not terribly common and are sensitive to heat - which is why they are mounted up front.

Good preventative maintenance is to take them off, clean up both sides and re-apply a new thin layer of thermal grease.

Just be careful when removing them, they are made up of two pieces and you can easily pull them apart if the lower half is stuck to the grease.

skpyle

Thank you for the clarification Hacker-Pschorr!

I have read stories of people just removing the modules to find the bases have stayed behind. That thermal grease hardens like glue.

I am still used to my GM roots of 70's-80's HEI where the module just ups and quits. I am not assuming the Bosch modules are the same. Just call it a little paranoia and I am good with spending the money for two new ones. The old ones will be cleaned up and kept as spares.

Very good point about the preventative maintenance.

Thanks!

Seth K. Pyle