2004 Toyota Prius body rust / corrosion (rocker panels, front fenders)

[MetroMPG]

The 2 large plugs I removed went back in tightly, but I can see your point.

If anyone takes the vehicle for a professional spraying, I would definitely show them the larger plugs so they can get their (large) wand inside the cavity. Typically they only drill access holes on top of the rocker (inboard of the door seal), and in the Prius' case, that means they'll only be rust-proofing the inner rocker compartment, not the outer one with the rust problems.

[Xist]

If you planned on keeping the car, would it do any good to cut foam to fit inside, so that it does not fill with debris?

[nimblemotors]

If you had a car made of all fiberglass...it would pretty much last forever.

[E.Roy]

In my experience, it is not just the holes that are causing the rust, it is much more the fault of condensation and poorly protected metal on the inside of the rocker. The poor coating is added before the panel is welded in place, so the spot welds become areas for immediate rust.

If you get snow caked on the rocker, and warmer air inside, you'll get water beads forming inside = rust.

Solution: as soon as you get a car, use the existing holes and adding holes if necessary to spray in oil based substance to coat the interior. I use CRC brand white lithium spray grease, WD-40, or similar with the tiny red spray straw to spray inside the rockers and fenders.

A totally easy spot to reach is on top of the wheel arches thru the trunk area, just pull back the liner or remove the plastic and spray on top, or use a brush to apply grease.

Again, I really think its the condensation that occurs, not the few holes here and there in the rockers.

[MetroMPG]

The amount of debris -- sand & fine grit -- piled inside the rockers in the areas by the rear drains where it's rustiest would challenge the idea that condensation is the main culprit!

If grit is getting inside, then so is salty water in the winter, which is much worse than pure condensation.

But condensation would absolutely make things worse, especially where rust has already started.

Regardless, spraying rust inhibitor from day one, like you do, is best.

[MetroMPG]

I drove the car through the winter with heavy duty black duct tape over the holes where I had cut the rusty sections out of each rocker.

Now it's coming up to time to sell the Prius, so the repairs have begun!

Before:



After:



Above: shows a metal patch butt-welded into the opening I had cut. I'm no pro welder, and the metal was perty thin in a few places, so I blew a lot of little holes while welding. I epoxied over the holes for a waterproof seal.

Next up: body filler & smoothing.

[Daox]

Looks like a good start.

[MetroMPG]

Skim coat of body filler:

(Yes, I'm this slow.)

[Daox]

Wow that is so low, did it even really need a skim coat?

[MetroMPG]

Oh, my metal patchwork isn't as smooth/flush as the photo might have lead you to believe. It does need a little filling/leveling.

Also, I ground down a few other spots where the rubberized undercoating was starting to bubble from underneath, and you can't feather-sand the edges of that stuff. Plus, it's pretty thick, so needs a bit of fill to make it all level.