Distributer cap & rotor

I just took off my distributer cap and rotor to clean them. For some reason I get some grey crystal like stuff on the contact surfaces inside the cap? Once in a while I scrape them off with a screwdriver.

Why do I get that grey stuff in the distributer cap?

The cap and rotor are now more than 3 years old. How often should these parts be replaced? I'm thinking preventive maintanance. Or should I simply follow the saying that goes; "if it ain't broken don't fix it"?


Since I don't have a digital camera I can't post a picture.

[pbs911]

I don't know the reason why the caps and rotors do that but I am sure it has something to do with electricity flowing through the contacts points. After 3 years I'd retire the cap and rotor and replace with a fresh set. With my 3.0 I would change them out about every 15K miles, which is probably overkill. They are not that expensive. On my 3.6 the cost to replace is >$100, so I plan on a little longer use, but before three years of daily driving.

[Decolliber]

I would imagine that stuff is corrosion from your damp North Sea climate. Get a can of electrical cleaner and clean it with a Q-tip or a toothbrush (not the one you use every day). I replaced cap and rotor two years ago and it only cost about $50.

[Early_S_Man]

Mikkel,

Is the contact area where the wire ends plug into made of aluminum, rather than brass or copper? If so, aluminum oxide is the deposit you found, and oxygen and moisture are the culprits!

Replace the cap and rotor, then clean the spark plug wire ends ... and put silicone grease on the spark plug wire ends to prevent the deposit in the future!

[ruf-porsche]

Could be from arcing or tracking as the spark goes from the coil into the rotor and back out into the spark plug wire. The rotor is not touching the contacts in the cap so for the electricity or spark to get from the rotor to the spark plug wire that is attached to the cap it must travel through the air like lightning hence you get an arc at the contact inside the cap.

Thanks guys. I guess I'm going to replace cap and rotor soon.