Sacrificial anodes and SS Exhausts

OK so here's an interesting one I heard the other day.

APPARENTLY if you have a stainless steel exhaust fitted to your car, the bodywork is more likely to rust

Supposedly it's to do with the fact that because the electrical systems are earthed to the bodywork there's a current flow. For some reason rust is promoted in a steel exhaust as a result. So by having a Stainless Steel exhaust, the rust takes hold in the bodywork instead.

I was drunk at the time but I distinctly remember the term 'sacrificial anode' mentioned...

Fact or Fiction?

 

How strange... I was just thinking about if the current through the body causes corrosion then I saw this post

In answer to your question though... I dont know

 

http://www.capsante.com/Articles/howto_sacrificial_zincs.htm

I think the key thing here is 'SALT water'

 

hmmmmm

Thinking about it... exhausts are really only connecter at the engine. Most are hung in the middle and back with rubber.. so there isn't a circuit being made.

 

Interesting! So what about gritted/salted roads in winter then? There may be some truth in it after all!

*runs out to rip stainless steel system off car*

 

But isn't the engine connected to the chassis via an earth strap? Hmm... *ponders*

 

Yes, but the actual exhaust pip itself only has one connection at the engine end. The other is insulated by the rubber hangers. Therefore no electical current is conducted *through* the exhaust.

 

Surely to have any real negative effect you would have to physically immerse your dub in seawater.

For a prolonged period of time too.

I dont think I`ll be removing my SS exhaust just yet ...
Edited by: superden

 

Good point! Except for like on my old Mini where it was so low the exhaust kept getting ripped off so I got longer U-Bolts and clamped the fecker through the floor!

 

* Totters off mumbling about design tolerances *

 

When you have 2 metals together rust, or the elements that cause rust, will 'attack' the most reactive metal.
I did remember something from college. This is often used to protect things from rusting and is known as sacrifical protection.

 

Its called Galvanic corrosion.

 

Its known as cathodic protection, they bolt zinc blocks on the hulls of steel ships, as the zinc is more chemically reactive than steel, therefore the zinc corrodes instead of the steel, the zinc doesn't rust, it corrodes as the only metals that can rust are iron and steel as rust is iron oxide.

Chemistry lesson over

 

So...

I'm alright with my stainless steel exhaust then or what?

 

yes! there's no current flowing through the exhaust...

 

Just park your car next to a Rover that will attract the rust away from your car.

 

This is definitely true to some extent, have to have a sacrificial anode on a car, but with more modern cars being made with galvanised steel etc then the problem fades rather quickly.

 

it's important for ships because they are immersed in a conductive liquid. Air (in the case of a car) is not a conductor

 

so how come my stainless steel exhaust is rusting

well, I say rusting, but it's more small spots of rust-like surface corrosion.


David.

 

Because you bought one made from shit grade stainless steel.