LuxInterior Reader
May 19, 2015 11:59 a.m.

My girlfriend gave me a one-owner 356k mile '92 Miata for my birthday Friday.

The good news: It runs great. Good paint. The engine has been replaced. The brakes were just done. The driver's seat has a just a little bolster wear. Surprisingly, It doesn't seem to need much other than shocks and eventually... a top.

The bad news: It has rust in the passenger rocker behind the door. The driver rocker shows no rust. So, other than keeping the drains clean, how to prevent the driver side from rusting through?

The former British car enthusiast in me says "oily things don't rust". Any value in squirting lots of WD 40 into the rocker drain hole? Other ideas?

kylini HalfDork
May 19, 2015 12:05 p.m.

When I paid a body shop to fix mine, one was bad and one was good. Both got drilled and flooded with POR-15. Here's to hoping!

WonkoTheSane Reader
May 19, 2015 12:06 p.m.

If you don't mind a bit of a threadjack, I was going to post basically the same question, except for I was going to ask how people kept it from rusting after welding in a new panel?

Tom Suddard Associate Editor
May 19, 2015 12:11 p.m.

For the backside of a repair, use "body cavity spray." It's fairly self-healing and flows well, so just spray it all over the backside of the new panel.

WonkoTheSane Reader
May 19, 2015 12:44 p.m.
Tom Suddard wrote: For the backside of a repair, use "body cavity spray." It's fairly self-healing and flows well, so just spray it all over the backside of the new panel.

Thanks for the info! We just rescued another 91 BRG for a friend, so this is very relevant to my (near) future endeavors! I figured there had to be an easy solution out there..

Edit: I'm assuming this is something I can get at Napa or my other friendly auto body shops?

Tom Suddard Associate Editor
May 19, 2015 12:46 p.m.

Maybe not NAPA, but any auto body supply shop will have it. I usually use the Wurth brand–it works great.

tuna55 UltimaDork
May 19, 2015 12:49 p.m.

3M rust fighter 1

pjbgravely Reader
May 19, 2015 12:50 p.m.

I use used oil, it sticks and it repels water. It also soaks into existing rust. On an exposed area you should repeat every year. In a hidden spot, unless there is water flowing through it once should be enough. I use a air powered engine degreaser wand.

NOHOME UltraDork
May 19, 2015 3:13 p.m.

Miatas are pretty rust resistant. The problem starts when the drains for the tops fail and flood the inner sills.

Since the inner sill and the outer skin of the quarter panel are in very close proximity, the water tends to stay in the space. Even if you flood with oil, oil floats on water and is not going to displace the water. Eventually the coatings on the panels succumb to the presence of water and rust happens from the inside out.

Here is a picture of the rocker panel structure after I removed the quarter panel. The brown bits are where the outer skin was in close proximity 1/16" to 1/8"? from the rocker panel.

Here is another picture to show you what you are up against. See the small crack where the rocker panel wraps around the wheel-arch? Once you flood that with water, the moisture is not coming out unless you flood the sill with a guttering agent like ICP that will absorb the water. If it so happens that the water was also salty when it got in, forget it.

I will tell you one thing, as a veteran of several MGB and Sprite tub rustorations, you would not want to bring a Miata back from the dead if it had a seriously rusty tub.

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