DenLip said:
Let's take a moment to explore this trail, shall we?
Mine is a '00... so it's not gotten into the rotted-floor syndrome just yet. But on my last couple of ventures underneath, I can see that various edges and welds are beginning to get a bit of crust on them.
What (if anything!) can be done to stop or greatly slow the progression?
I've owned two kinds of cars in my life - old crappy ones that weren't worth putting a lot of effort into... and new ones that didn't need any effort. My Jeep is the first "tweener" I've owned!
Undercoating? A trip to Ziebart? Oil?
Thoughts?
WATER is the closest thing to an UNIVERSAL Solvent man has found. Thats your enemy.
Actually its oxygen that causes rust, and metal will rust exposed to just air, BUT, water is 1 part Oxygen and 2 parts hydrogen, so water is much more effective at creating that galvanitic electrical reaction and providing the oxygen for the rusting.
It impossible to keep water off the bottom of the car, but you want the car to dry off as soon as possible and not have places for the water to get trapped and spend days in some nook or crannie that lets it start the rot.
The paint does a pretty good job of keeping the water off the metal, but dirt and chemicals (especially salt for de-icing roads) breaks down the paint.
So keep the underside clean is the most important preventative step. Everytime I wash my cars, I spray the hose all up under the body to flush away the big dirt and chemicals, once a year, usually summer, I take the time and discomfort of getting soaking wet by washing the underside of the car thoroughly. I've had three cars that came with no undercoating what so ever, just the factory paint on the underside, and just the occassional fresh water rinse and yearly cleaning of the underside prevented any rust what-so-ever for 11 years or more on all three. (I lived just outside the Salt Road Belt, MD, NC, CA, PA is barely in it).
Repairing the floor pan is always easier the earlier you do it. Just remember to keep bare metal coated and water out of the nooks and crannies.
Sounds like you need to clean the bottom of your XJ. Then use a wire brush to brush away the crust on the edges of the sheet metal. Get something to coat any exposed metal, lots of people will moan when you say your using Rustoleum paint on a car, but its a lot better than doing nothing at all and its cheap and pretty darn tough. Spend the $10 on 2 small cans of Rustoleum primer and paint and a brush, with some sand paper and touch up any paint problems underneath.
Finally sealing up the underside, this looks like where the XJ is pretty weak, there is a lot of nooks and crannies on the underside of the XJ that water can get trapped in and spend a long time before it evaporates. I'm considering sealing up all those nooks and crannies on the underside of my XJ after I finish the floor pan patching, get some seam sealer and running it all along the edges of the crossmembers and frame rails, work it in, like putty with my finger, to seal water out of those areas. It looks all the rust I have on my USED XJ, started from those nooks and crannies that held water in there and it didn't evaporate right away like the rest of the floor.
If you've got rust already, you have to get rid of it. The reason they call RUST CANCER, is because it acts just like cancer, it continues to grow until it consumes the host, even if you get rid of it, if you leave behind just a tiny bit, that only slows it down and it starts to grow again.
If the rust is bad, you have to cut it out, all of it, cut back to good metal, then repair the hole with patch metal.
If its just surface rust, you have remove it all;
*Grind it down, all the way to fresh metal underneath.
*Brush it off with a wire brush and sandpaper.
*Dissolve it with Naval Jelly.
There is Rust Neutralizer , which chemically reacts with the rust.
It doesn't work as well as totally removing the rust, the rust can and often does start again, but it may put off the continuing rusting for years. Obvsiously knock off as much rust as possible then use this stuff, then paint an seal it, to keep the moisture out.
Undercoating, Ziebarts and Bar & Chain Oil, help keep a well protected underside even better protected. Remember, these things don't last and either wash away or let water in underneath them and the rust starts. You have to redo these every year or couple of years as well.
My USED XJ underside looked fine, dirty, but all the undercoating looked fine. When I started to tap around with a claw hammer, I had chunks of undercoating falling away with the rusty metal. So my floor either rusted from the cabin side out (very possible considering how poorly the prevous owner cared for the vehicle) or moisture got past the undercoating and it hid the rust as it rotted out the big holes in the floor pan. You still have to keep undercoating clean and moisture free.
