Cleaning / Removing undercoating. Good idea?

[Panici]

Hey guys,

So I have my rear subframe out as I'm refreshing everything on it. Meanwhile, I got a good look under the rear of the car.

How far should I go cleaning this up? It doesn't need to be pretty, no one will ever see the underside of the car. (Although that hasn't stopped me from making my subframe refresh look mint)
My primary concern is keeping rust away.
My second concern is to make my life easier in the future by working on parts not covered in undercoating.

Is this undercoating any good for rust prevention? Or will it just absorb and trap water every time I drive in the rain? (and then rust underneath)


Half of me wants to strip as much off as possible (first with pressure washer, then with grinder/drill etc), although that will be a messy and time consuming job (on my back in the driveway).
The other half of me says to just hit any rusty areas with a wire wheel/flap disk, then shoot some Eastwood rust encapsulator on them.


How far would you guys take this?

[bangn]

with the rusty areas, are they areas that didnt get painted with underbody sealer that have eventually rusted? or is the rust under the sealer.

It only looks bad to me because the fuel tank is rusting away

Ive removed sealer from the bottom of a car before and its not a job I would ever do again unless it HAD to be done and there was no other way. I also found when removing it there was no rust at all under it.. It was just caked with oil and grease. Alternatively I should of just sprayed it with a degreasing cleaning solution and scrubbed it with a hand broom and high pressure the shit off..

The small areas I am seeing I would buzz off the surface rust with a wire brush on a grinder or drill and spray with a rust converter and re-paint it.

The tank really has to be removed to attend to all that properly, it looks like the rust has made it way between the tank seams but. To start with I would remove the rusty parts off the car and see what you are left with.

[efficient]

You should drop the tank and replace the top fuel lines since you already have the subframe out and clean up the tank in and out. I say you degree it and power wash it as most that you can and then hit if with a wire wheel and por15 all the rust.
BTW if you decide to drop the tank and replace the top hoses I'd recommend oem. I had to redo it because I bought hose from auto zone that started cracking

[mbonder]

From the looks of it, the rust you've got there is mostly on the fuel tank, not on the actual body of the car. I wouldn't take any of the undercoating off the body of the car, it is pretty darn effective in keeping rust from starting on the shell. If you've gone that far and you can afford a few extra hundred bucks, why not replace the tank while everything is out? You can do the lines as well and you'll never have to touch the subframe again. The current tank will eventually rust out and you'll have to do the job all over again in the future otherwise.

[Northern]

Is this undercoating any good for rust prevention?

Think about it. Your car is what, almost 30 years old? Do you think the bottom of the car would survive 30(potential) years of salt/sandblasting if the undercoating weren't good?

Half of me wants to strip as much off as possible (first with pressure washer, then with grinder/drill etc), although that will be a messy and time consuming job (on my back in the driveway).
The other half of me says to just hit any rusty areas with a wire wheel/flap disk, then shoot some Eastwood rust encapsulator on them.

Any spot of rust is probably from the undercoating/paint getting damaged, initial application failure, or seams/voids/cavities/dissimilar metals. I'd grind back the bad spots with a knotted wirewheel, grind the rust, prime/paint/seal, check the back side of where you were grinding to check for paint damage from heat, then spray some undercoating like Fluidfilm in/on any seams/voids/cavities/fasteners etc. Sure it makes it greasy to work on, but that's what gloves are for.

[jtparts]

You should drop the tank and replace the top fuel lines since you already have the subframe out and clean up the tank in and out. I say you degree it and power wash it as most that you can and then hit if with a wire wheel and por15 all the rust.
BTW if you decide to drop the tank and replace the top hoses I'd recommend oem. I had to redo it because I bought hose from auto zone that started cracking

If you buy the Goodyear hose with the blue liner inside its good stuff in case oem isn't handy.

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[jtparts]

Undercoating is necessary. Manufacturers have spent a lot of money learning how to save money by cost reduction. Primarily by eliminating things that don't reduce warranties and car sales. Yet they still undercoat.

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[Panici]

First off, thanks for the advice guys!

From what I've read after a quick google, the rear subframe doesn't have to be out to replace the gas tank. As I'm pretty tapped out budget wise right now, I'm just going to clean up the rusty spots on it.

You've convinced me to leave the undercoating as much as possible. Any loose areas, or rusty spots that have come through I will address.

Since the weather is nice right now, I'm going to go have a go at it!

[estoguy]

Think about it. Your car is what, almost 30 years old? Do you think the bottom of the car would survive 30(potential) years of salt/sandblasting if the undercoating weren't good?

This. My Eta is a Canadian vehicle and has been undersprayed many times before I owned it, and yearly since. The factory coating combined with the rust spraying has been great... the underside of my car looks amazing, and I've now been driving it daily for all 4 seasons for nearly 4 years.

Just fix what needs fixing.

[kway]

Hard to tell on my phone, but it looks like most if not all of that is the factory schutz. Many times better than that garbage that comes out of the aerosol cans from the parts store. Even if you were to try to get it off it would be a fool's errand. Very difficult and ultimately counter productive. I'd only go that route if you were stripping it for a serious race tub, or maybe shiny undercarriage full show car. Even then...