I have a 240d with rust at the bottom of the door. I'd like to stop the rust and find a close matching paint to hide it as best as possible.

I was thinking about sanding off as much as possible and using some por-15 and then getting a can of yellow/cream spray paint to cover the por-15.

Does anyone know what color best matches a cream/light yellow w123?

I read that por-15 shouldn't be in direct sunlight so it's probably best for under the car frame/floor panel rust.

Any suggestions?

Thx.

pete

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Use fluid film, works great. However with rust, they'res more than what meets the eye.

https://youtu.be/dWHMGVyPdoQ

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1998 Ford Escort ZX2 5 speed - 279,000 miles My Daily

1992 Mercedes 300D 2.5 202,000 - Pure junk
2000 Mercedes E320 Black - 136,000 miles - Needs repair

Don't forget to grease the screw and threads on the spring compressor.

Fluid Film (or a homemade version) is really more for preventing rust, especially where you can't see/reach. For that cosmetic rust, yes sand it down and get it taken care of. POR-15 is good, although you better buy small and have a few projects in mind because it will completely solidify in the can after a time. I prefer the paint-on rust converters like Permatex Rust Treatment. I tested several of the liquid and spray types but they just don't work as well. This stuff is a thin white paint that you put on the rust and then it turns black when it's ready to be painted over.

But pick your poison, definitely get it taken care of. Don't just squirt oil on it.

-Rog

I first use Locktite Extend Paint Over Rust with Extend Rust Neutralizer from Loctite Adhesives This converts rust to a stable form that can be painted over. Do not sand the rust off as this product won't help if you do so.

As for top paint, use Rustoeum ( the original over rust paint, not their " Painters Touch " plain paint ) Get regular cans of while and yellow and mix up the color you need. After a while you will need to lightly scrape and repaint as the thick rust flakes off.

can't speculate on how deep and extensive the rust is - but I used the POR 15 kit - that includes the degreaser and metal prep as well. remove the trim. sand it all down, and follow the POR instructions. I would also spray a bunch of 3M cavity wax inside the door (before the degreasing/POR application).

If you desire, you can get your Mercedes paint code mixed in 12 oz aerosol cans for about $20, and a can of clear cote for about $8. i used a place called automotivetouchup - but their site appears to be down at the moment. I painted one of my rear fender lips and it was a perfect match. I used a good quality primer on top of the POR, before applying the paint and clear coat.

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Andrew
Montclair, NJ
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1982 300D Turbo
120k
Petrol Blue Green

The only issue with using POR in the light is that it fades or discolors. That can be corrected by painting the POR. Go to the POR site.

The truck in the vid above didn't have rust so the only issue was preventing rust. You probably have existing rust. POR can stop that but it has to be applied correctly and gotten down into the cracks to seal.

I have a Dodge Cummins with a little rust in the door. I treated the outside a while ago and rust is becoming apparent again. This truck isn't worth the effort of new door skins but I intend to sand and re-POR with the addition of some POR inside the door.

I have a 78 Datsun Z that I'm getting back on the road. My intent is to treat the rust I can see and drive this summer. I'll take it down and have more extensive work done this winter.

Do buy the small cans of POR. Put a plastic bag between the can and lid when sealing. That will extend the life some. Factory sealed cans last a long time. Use a correct tool given away at paint stores to open the can. Screw drivers mess up the lid and it won't seal properly. Wear gloves unless you like the color on your hands (for several days after).

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Phosphoric acid AkA Prep & Etch is great rust remover.

Try it out.

__________________
1998 Ford Escort ZX2 5 speed - 279,000 miles My Daily

1992 Mercedes 300D 2.5 202,000 - Pure junk
2000 Mercedes E320 Black - 136,000 miles - Needs repair

Don't forget to grease the screw and threads on the spring compressor.

That is the active ingredient in Permatex Extend. It does not remove rust, it stabilizes it.

I beg to differ, I'll remove rust on some pliers in a few and upload it.

__________________
1998 Ford Escort ZX2 5 speed - 279,000 miles My Daily

1992 Mercedes 300D 2.5 202,000 - Pure junk
2000 Mercedes E320 Black - 136,000 miles - Needs repair

Don't forget to grease the screw and threads on the spring compressor.

Yep, I was thinking of Tannic acid for rust conversion.

https://www.theruststore.com/Rust-Converter-FAQs-W48.aspx

Rust Converter FAQ's

What is Rust Converter? Rust Converter, a water-based primer, contains two active ingredients: Tannic acid and an organic polymer. The first ingredient, tannic acid, reacts with iron oxide (rust) and chemically converts it to iron tannate, a dark-colored stable material. Tannins are a group of water- and alcohol-soluble natural products extracted from fruits, trees and grasses. The second active ingredient, 2-Butoxyethanol, is an organic polymer that provides a protective primer layer. The overall chemical reaction converts rust into a stable, black protective polymeric coating that serves as an excellent primer for both oil and epoxy based paints.

The only way to stop rust is to keep water away from it. Rust attracts/holds moisture Water is a constant source of oxygen. Steel must be encapsulated from oxygen to not rust.

Bondo and spray paint does not stop moisture from passing through it, despite what most people think.


Remove that trim piece and chip out all the rust you can, then wire brush it. If a hole has rusted through into the door, take the door card inside off and look inside the door and see what's going on in there. Water always gets into the door and is supposed to drain out a few small holes along the bottom of the door. If you don't have a bunch of crap clogging the drains in the door consider yourself lucky.



Anyway, start by removing that trim and cleaning everything up to see what you're really looking at. When you're down to metal with just a tiny amount of surface rust, and no drain problems with the door itself, then you are in a position to stop it.



There are several ways to treat and encapsulate the metal after that. IMO phosphoric acid (not the milky stuff) is good prep, POR15 is good on rough surfaces (it basically like polyurethane plastic) but it must be covered with something. I use thick epoxy putty to fill any holes - no very sandable but it's awesome. Paint over that.


Fluid film (and things like it) are for areas that can't really be accessed or are not worth painting - like underside parts or the inside of panels, or like inside you're door after it's cleaned out and maybe dowsed in a rust treatment. It's basically saying F U to rust but not caring what it looks like. The best ones are cosmoline or sp-400, nasty stuff. The liquid can be painted on with a brush, easy. If you get the little spray can version, have a respirator- that mist can suffocate you..

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1985 300TD 1981 Scirocco 1.6D conv 1986 Golf 1.6D 2003 Golf TDI

Yup, you're right, it technically is a rust converter.

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1998 Ford Escort ZX2 5 speed - 279,000 miles My Daily

1992 Mercedes 300D 2.5 202,000 - Pure junk
2000 Mercedes E320 Black - 136,000 miles - Needs repair

Don't forget to grease the screw and threads on the spring compressor.

Two options:

1) Grind it away, weld in new metal, prime and paint.
2) Remove remaining paint to a thin, non-flaky rusty surface, convert, then prime and paint.

#1 will be the superior result, though more involved and costly.
#2 will have a high likelihood of rust coming back.

Regardless of which you choose, Id highly recommend that you remove the door card and vapor barrier, and spray the interior of the door with either a creeping oil (Krown or Carwell is best), Lanolin (fluid film), or wax (cosmoline or Amsoil HDMP).

Depending upon what you find, Id likely treat the good areas with Amsoil HDMP followed with Krown or fluid film, and any areas inside that have exposed rust, Id repair first with a similar approach to the outside, then coat.

Dont put a waxy coating over exposed rust. It facilitates moisture being kept therein. Id use a penetrating oil like Krown, followed by lanolin.

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)

I have had good results with my conversion / rustoluem. The key is to clean and repaint when rust bubbles through, eventually rust will slow and there will be less rust returning.

Ultimately the quickest, easiest, and by far the "best" possible repair is to find donor doors at the yard. I think the Pull-a-Part still has them for around $50+ bucks. You can pull an entire door and re-install it probably in less than 4 hours and you will never have an issue. The trick is finding the same color without damage. If you have a "common" color , then the task should be easier unless you had a rare color ... Just a thought. Keep in mind a little rust is never a little rust. I would have to say by far the biggest issue in a W123 is finding one without rust or rot. Then, no wrecks. If you can find a true survivor, then your repairs and restoration is truly half way over ... Even the tiny rust under the battery tray or the tiny line under the passanger seat can be a major headache to repair properly. Go for donor repairs everytime if possible. You avoid all the messy repair and long term problems. Even the true pro's at rust repair do not have a great fix except true metal replacement and even that will rust out if there is any type of compromise.