As soon as I got back home with my new 4Runner (here in Alabama), I quickly researched undercoating methods.

Since my runner had endured 4 years of harsh winters in NY, the underneath had a ton of surface rust. Granted, it only had 22k miles on it when I bought it and the paint was in near show quality condition, but the underside looked like it had multiple nukes exploded underneath it.

Check out: POR-15. Contact them and get as much info about the product as you can. Then ask them for a dealer in your area (you cannot buy from them directly) and they will be able to sell you the product. They also sell a product similar to a paint "primer" that goes on first. You might want to consider that. (Personally, I did not opt for it.)

POR-15 is a popular name in the undercoating business...as this is the stuff I used. You simply have to "paint" it on w/ a paintbrush...unless you're able to get an air gun and spray it on. It is a PITA to apply and the entire process is very labor intensive. Plan to dedicate an entire weekend to this project if not more - this includes the application and drying time. However, if applied properly, por, will probably outlast your vehicle and protect your vehicle from the formation of rust and stop the spread of any existing rust.

I have a set of ramps that I used for this project. After you've got your 4Runner up in air, it's time to remove all the loose rust. I took my cordless drill and hooked a metal brush attachment to it and went to town sanding down the entire underneath. Oh yeah, if you don't already have a mechanics creeper, get one. Mine came in very handy.

Then you begin to apply the product in stages. There is a "prep" stage with one product and a "finish" stage with another product. The finish coat should be done in 2 coats. You also have to apply the finish coat rather quickly, because when you go to apply the 2nd coat, you don not want the 1st coat to be dry. The 1st coat still needs to be some what "tacky" to the touch when you go to apply the 2nd coat or it will not adhere properly. Once you are done, the vehicle has to sit for 24 hrs to dry.

Like I said, just call POR customer service and they can give you better info than I can about it. Just be careful not to get any of the stuff on your skin. If you do get it on your skin, it will not come off for at least 7days. Trust me, I know. Wear multiple layers of clothing from head to toe. (Kinda sucks you've decided to do this in the summer. That's probably one reason I did not wear enough clothing.) I wore jeans and a long t-shirt and after I was done, I was covered from head to toe in this stuff. The bad part was, some of the larger spots soaked through my clothing and got on my skin. I had big black spots all over my body for a week. (Looked like a milk cow for a week!)

Now, for the "quick-n-easy" fix that works just as well IMO, check your local auto parts stores...ie Napa, Auto Zone, Advanced Auto or something similar. They stock many different varieties of undercoating in aerosol spray cans. Cannot think of any brand names off hand, but if you go this route, buy a few different varieties and test each one before you decide on a final selection. Some cans go on thicker, while some produce a "brown" colored undercoat and others produce a "black" color. I prefer black myself. Do get something in a "rubberized undercoating" if you go this route. I've had the best luck with this type. (Again, if you'll check my 4Runner profile, you will find a picture of the underneath of my driver side slider. There you will see a picture of this rubberized undercoating I'm describing.)

I've used both por and aerosol spray cans as mentioned above on the underside of my 4Runner and truthfully, the rubberized undercoatings found in spray cans are just as durable and are much easier to apply. Touch ups are much easier if needed as well. Less mess too!

Here is a third option - You can even go to some Toyota dealers and they will undercoat your vehicle for you with their own product and equipment. Granted they will charge you and it will probably look lke crap when it is done, but I am just making you aware of this option. I looked into this before deciding to do it myself.

Also, Google the following phrases:

1. Vehicle Undercoating
2. Rubberized Undercoating
3. Aerosol Undercoating

That will turn up even more ideas than what I have mentioned. I have heard good things about the 3M Rubberized Undercoating. Be sure to look into that one.

Now if you have a spot on your frame that rust has completely eaten through, then that is a different story...can't help you there. But if you simply want to keep the surface rust from spreading and/or forming, the ideas I've listed above will guide you along the way.

-Rock

POR-15, much experience with most of car except outer skin painted with it.
+ almost indestructible, can't be chipped, impervious to water and most
chemicals (wipe it off with Acetone and brake fluid takes months to
attack it). High gloss surface. Flows out well with brush marks almost
disappearing (I sprayed most of mine). Cures very hard overnight.
- contains Isocyanates (very toxic) and respirator (best available and
fresh) or fresh air system and face shield should be used when spraying,
good ventilation (and respirator probably) when brushing. If you get it
on your skin you wear it. Limited shelf life once opened (weeks, months
depending on how well you seal it and how much water got in while open).
Prep degrease must be good - will fisheye with contaminants. Expensive (~$30/qt)

Zero-Rust, much less experience recently got a couple of rattle cans and
used on small parts. I painted the black parts of my ZF with it, topped
with their clear. Looks very nice. Didn't learn of it until after most
of my painting was done.
+ goes on very nicely (semigloss) and easily. Supposed to have 2000 hr
salt spray test. Good shelf life. Non toxic. More color choices. Cheaper
(much ~$11/qt I think). Available in spray cans.
- not solvent or immersion water resistant. More brittle and can be chipped.

I don't have first hand long term experience with either. Others that do
think both are great.