What causes this on a distributor cap?

[fxeditor]

Hi all,

I am doing a tune up of my 1987 Coupe when I ran across this problem. I pulled the plug wires going to the distributor cap when I saw the #1 prong covered in rust! Please see the picture below:




This cap is only about 2 years old. What causes a problem like that? Moisture trapped between the plug and wire? I haven't pulled the plugs yet to see their condition but I'm assuming the #1 plug isn't going to look great either!

Thanks for looking,
-Michael

[GaryR]

Rust is the name of iron oxides that forms when iron corrodes and is caused by the reaction of iron with oxygen. Rust is formed when oxygen dissolved in water reacts with iron. There are always two different reactions in a corrosion process:

1) oxidation of Iron
2Fe ---> 2Fe2+ + 4e-

2) reduction of Oxygen
O2 + 4 e- + H2O ---> 4OH-

The overall reaction is:

2Fe2+ + 4OH- ----> 2Fe(OH)2

Fe(OH)2 reacts with oxygen to form Iron oxides: Fe2O3 (hematite, red rust), Fe3O4 (magnetite, black)

[fxeditor]

Originally Posted by GaryR

Rust is the name of iron oxides that forms when iron corrodes and is caused by the reaction of iron with oxygen. Rust is formed when oxygen dissolved in water reacts with iron. There are always two different reactions in a corrosion process:

1) oxidation of Iron
2Fe ---> 2Fe2+ + 4e-

2) reduction of Oxygen
O2 + 4 e- + H2O ---> 4OH-

The overall reaction is:

2Fe2+ + 4OH- ----> 2Fe(OH)2

Fe(OH)2 reacts with oxygen to form Iron oxides: Fe2O3 (hematite, red rust), Fe3O4 (magnetite, black)

Thank you professor Smart A**. Why is it on my distributor cap?

[dshepp806]

Because of the H2O piece of the equations...

Doyle

[Neel]

Nice chemistry lesson, Gary.. Michael, I use silicone dielectric grease at the connections, both cap and plug, to keep this from happening...

[Targalid]

Because you live in California and not in the salt capitol of the world, on the east coast, I suspect that on this single lead that you had some contamination. This is what we see happen to our cars where the roads are salted in other parts of the US. You had the unfortunate experience, though a minor one, or having this happen to a single contact on your distributor cap. Any humidity in combination with salt accelerates corrosion of ferrous metals via a process called chelation. It also isn't too good for most other metals as far as that goes. I suspect that when the cap was installed, the person who did so perhaps had some salt on his or her fingers (potato chips plus beer = better mechanic experience) and touched this single contact point. As the previous poster says, use some dielectric grease next time and it will help minimize this occurrence. Most caps and wire sets come with a small packet of grease for this purpose.

[dshepp806]

I ALWAYS clean the hey out of those connectors (even an occasional burnish),...Bosche dielectrical grease galore,..then physically mount those babies as tightly as possible...I've never seen such as demonstrated in the pic...that is pretty wild, you must say. Clearly moisture prevailed there.

Get her changed out and go from there!

BEST!

Doyle

[fxeditor]

Thanks for the help on this everyone! You're absolutely right TargaLid Being a socal lad, I really haven't had too much experience with this "rust" thing you speak of! That being said I ran down to my FLAPS and bought a bunch of dielectric grease which I'll be using on both ends of the plug wires.

Take care,
Michael

[Targa Me]

In all my years of working on cars, I have never seen rust on a Dis Cap like that.
My 911 is a DD and is in the rain during the winter seaon and I've never seen that.
i think its odd.

[tazzieman]

2 questions:
- The condition of the boot on the lead attached to this terminal? Microscopic split?
- Did you notice any symptoms? The 911 will run quite well on 5 cylinders , and on 4 though then it has the pull of a VW Beetle. The plug condition - please report back with a pic.

[DanielDudley]

That was wet in the cup for a good while.

[docrodg]

Originally Posted by DanielDudley

That was wet in the cup for a good while.

That can't feel good, especially when walking!

[fxeditor]

Originally Posted by tazzieman

2 questions:
- The condition of the boot on the lead attached to this terminal? Microscopic split?
- Did you notice any symptoms? The 911 will run quite well on 5 cylinders , and on 4 though then it has the pull of a VW Beetle. The plug condition - please report back with a pic.

Thanks for the reply! I got called into work for an emergency so I wasn't able to pull the plugs yesterday. I'll knock that out today and report back.

As far as the plug wire goes, it is a 2 year old Magnecor wire. I checked the boot for any splitting but didn't see anything.

I was experiencing symptoms. Rough idle, lack of power, and a failed smog check (lean condition) all prompted this tune up.

-Michael
.

[Jared at Pelican Parts]

Water causes that. Use a dab of dielectric grease on the boot next time.