Bi-metallic corrosion?

Girlfriend's daughter asked me to look at her car ('08? Nissan Versa), because something was rattling. Well, first she asked for duct tape... I took a look underneath and one of the heat shields over the exhaust was loose. All four of the mounting holes through the flimsy aluminum were big enough to pass over the nuts that held them to the body. My assumption is that the aluminum / steel contact corroded through.

My plan* is to put some big ass fender washers on it, too cover the enlarged holes. But, what can be done too prevent further galvanic corrosion? Smear some copper on it?

*Yeah, the GRM way is probably to toss the shield, but her dad, my girlfriend's ex, is a dick. I don't want him getting bent out of shape, because I "fixed" her car like that. I don't know if he even looked at it, but his response to her having a car issue was, "Take it to the dealer."

Uhhh, that shouldn't have happened... I would fender washer the hell out of it but it sounds like it wasn't tight from the get go and rubbed through, got pics?

Switch to stainless or zinc plated bolts and washers too.

Fender washers and a liberal painting with high-temp RTV to prevent it from happening again?

Most of the heat shields on my Jeep have done the same thing, usually complete with flaky corrosion on the aluminum around the holes. Stainless hardware should mostly resolve the issue.

Fender washers, yeah, that. Or ditch the covers. Done that. And if you're concerned about her father being a dick, have him fix it for her.

In reply to Dr. Hess:

His idea of fixing it is taking it to the dealer. He won't pay for it. She's a college student. It's no trouble for me to throw some washers on it. I just want to prevent the need to do it again.

My point was that if the father was going to be a dick, she could do without.

If you can get a fender washer to work on that, do it.

Move southwest by about a thousand miles? The fender washers should hold it for another 10 years, by then it will be scrapped due to rust or a full blown beater.

Fender washers did the trick. Hopefully, she'll be in another car, before it becomes an issue again.

In reply to BrokenYugo:

The bottom of the car is immaculate. Like no other car I've been under, in Wisconsin.

Happens all the time, did one today. Throw a fender washer on it and it'll be good.

Don't worry about any paste on it. The first small washer took almost 10 years to wear/corrode through, a big fender washer will take even longer.

Edit: oops I see I'm late!

Since nobody suggested it, a sacrificial anode?

Ah, the washers will work fine.

FlightService wrote: Uhhh, that shouldn't have happened... I would fender washer the hell out of it but it sounds like it wasn't tight from the get go and rubbed through, got pics? Switch to stainless or zinc plated bolts and washers too.

You clearly don't live where they use salt on the roads!!!

In reply to NGTD:

Dealt with it in Marine...that has salt.

That set up is supposed to be inert, aluminum to stainless/aluminized exhaust. So that means they didn't use zinc coated fasteners, which is (apparently that should be "was") the standard.

The chart in the Big Book of all Knowledge of Things states this.

It also brings up Fretting Corrosion, which is where a chemical reaction is catalyzed through mechanical working. (Vibration in exhaust causes the salt to be more corrosive) Based on that photo that is what happened.