In general, when a late 80s or early 90s MB has a rust spot as shown in the attached photo, how bad can I expect the rest of the car to be? Is rust like this caused by an accumulation of salt on the inside of the panel or did a stone chip go unattended for too long? Should I fear the worst if I were to pull the plastic cladding to address that spot?

This picture is off a W124 in eBay.

Thanks,
Sixto
87 300SDL

spot could be from an accident repair. it is impossible to duplicate the factory prep and so often rust results from repairs. they will particularly show up at edges and ridges where the power sanders will concentrate the sanding and take it down to bare metal.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I can sure relate to this. I've done some cheap rust repairs on the van. Sanded down to bare metal, light fill the surfact pitting with Bondo, prime and paint. Not for show........simply to stop the rust.

Two years later, rust appears in the exact same area. My feeling is that the rust remained inside the steel and it's impossible to completely remove it once the pitting has occurred.

If there are any tricks that I'm missing, please advise. I constantly chase rust on this van..........and I'm losing the battle.

I just placed an order for a kit from por-15 ...I'm going to give that a go. I've always operated under the "the more affected metal you can remove the better your chancers are" assumption....

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Rob M
Norwich, VT USA
1980 240D Euro delivery 4 speed manual silver/blue
~160K miles

Rust, like cancer, will return if you don't remove all of it.
There are some metal treatments that may work. Claims they turn rust into primer. I've no long term experience with them.
Anyone with POR experience?

I firmly believe that the rust preventative/undercoating on a Benz is excellent. The rust on my MB is happening in different places for different reasons, but almost always from moisture trapped against a surface, not salt. Plastic side panel mounting holes, rear quarter and floorpan rust from leaky rear window, spots behind plastic inner front fender panel, spots near front cowl where leaves blocked draining, road sand in jack points (probably aided by salt here), etc. In testament to the metallurgy of the affected metal, my rust is highly localized, unlike the huge sprawling blooms typical of domestic iron, such as my 80 Chevy pickup!

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

The lower cladding on my 126 is attached by metal clips. The clips scratch the paint off on the body and the body and the clip itself rusts.
It is good that most of the rust is under the cladding where a cheap repair is not visible but bad that the rust can't be easily seen to stop it early.

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82 300D....went to MB heaven
90 350 SDL....excercising con rods

I have a little rust issue as well on a 95 W124.

The pic shows the roof just above the windshield seal.




I tired resizing the pic but it didnt go too well, sorry.

Today I will go to a body shop to see what they can do about it.

Don't use Bondo. It absorbs moisture.

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'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)

right about now I'd appreciate if someone would post something like "I used POR-15 and it reversed corrosion, improved mileage, and solved all kinds of other problems"... I figure in a week or so I'll have my own experience to share....

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Rob M
Norwich, VT USA
1980 240D Euro delivery 4 speed manual silver/blue
~160K miles

recently i repaired a significant amount of rust damage on my 90 300 te 4 matic.most of the damage was located under the lower plastic trim panels.the front of the rocker panels seems to be a bad place for dirt and leaves to accumulate.i removed with no exageration about 5lbs of crap from this area.definately recommend checking this on a yearly basis.to acheive success with any rust repair you must sand or media blast the affected area to remove any trace of corrosion getting down to clean metal.next step is an epoxy 2 part primer to seal permanently followed by several applications of a "high build" primer with fine sanding between coats.i finnish with basecoat/clearcoat to blend using a small airbrush perfect for small spot repair.this technique will give a longlasting repair that will look good from the curb.

I've been involved in restoration/maintenance of older cars for some years. I usually figure that what I see on the surface is 15% of what is going on underneath. Rust is like an iceburg. You only see a little of it from the top side.

I used POR15 on the floor pans of a car after it developed some rust due to heat/moisture over the exhaust system. It flaked off after a while. I tried applying it after wire brushing surface rust off, and I tried it directly over the rust. No significant difference. It dried thick and hard, but it had poor adhesion. I've read the testimonials, just like you have, but my experience was not consistent with their ads.

I have found exactly one solution to rust: cut it all out and replace with new metal. Grind the metal clean and clean it carefully with a tack rag. Do not let it sit before priming and prime with a self-etching primer/surfacer. As long as you do not expose any metal while blocking the surfaces, you can take your time from there on.

We would all like to think there is some majic elixer that will stop rust dead in its tracks. Again---not in my experience. After replacing most of the bottom half of a car that looked pretty good from the surface, my reaction to rust in any prospective purchase is to RUN AWAY.
Mark
93 300D 2.5 turbo
99 Crown Vic Police Interceptor
61 R-R Silver Cloud
66 Mustang restomod

I've used POR15 on one small spot and it seems to be holding up well. I was unable to get it deep under the window seals where the rust seemed to extend, so it is not a thorough job. On the other side of the car is the biggest rust patch, which I sanded with a dremel and slapped on one coat of POR15, but never got the chance to put on the second coat. The first coat is no good now because it's been exposed to sun too long, so I just need to start over. Couple things with POR15 ... leave a small amount of rust because the stuff adheres to the uneven surface better. Use Marine Clean first, then Metal Ready, then POR15 and do two or three layers. I've only had it on that one spot since about March (April maybe? I'd have to check my records), and it's done well so far.

The best way to stop it is to replace the area, as several people have pointed out. That said, I would think an uneven or lousy job could create a situation even more prone to rust.

If you're looking to slow or temporarily stop the problem, I recommend POR15 ... it doens't look great but it buys time.

I'm taking my 124 to a trusted body shop this week. I simply do not have the means to do the POR15 job I want to do (no garage, bad weather, little time), and I can't just let the car get worse and worse while I wait for the right conditions to do the work myself. The guy I'm taking it to is very good, and also will be cool about helping me attack it in the most affordable yet functional way. Hopefully the price tag won't be out of my range. I can't let the situation get any worse.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)

I agree with Mr. Delano from a few posts back. You cut out old rust, put in bondo, it gets wet and traps water. Then contact point of the bondo and metal rusts out in a ring.

A friend of mine put himself through college in the 70's doing rust repaints in Buffalo. I was the "works for beer" guy who hung around trying to learn his tricks. His technique was to cut out the rust and form a new panel of galvanized sheet metal as a patch. He would overlap the good metal by about 1-2". He would then use a brick behind the metal as a form and hammer to make a small divet or indentation in the overlap area along the seam. The rivets went in divet so they did not show. Bondo in the small overlap area / divet only to cover the seam / rivets. Roofing tar or undercoating behind it to prevent moisture from getting in. A gallon of Dulux enamel and the car looked great for a couple of years.

Chuck

I have used a product called Rust Bullet to hit a small rust spot in the rear wheelwell. It's supposed to be just like POR only with much better adhesion. It's best to get both sides of the affected areas also. Otherwise the rust keeps right on truckin'.

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'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)