Killing some rust

Ok, so I have this car, and it’s got some rust at the bottom of the wheel wells front and rear. Damn these Illinois winters and the salt!

I digress.

I have a plan to “restore” this car, and by “restore” I mean, “doesn’t that look nice for a car of it’s age?” Not really going for “show car” here. So, here is my plan, poke some holes in it if you would:

Step 1: Sanding entire area about 3 inches or so out from the rust in all directions.
Step 2: Grinding remaining rust, when and where appropriate as needed.
Step 3: Rust converter, and lay it on thick.
Step 4: Clean and examine area and rest of car for remaining rust (note, already looked over everything structural I could see, looks pretty good)
Step 5: tiger bondo for holes
Step 6: Regular bondo to smooth out
Step 7: Sand and prep for paint.
Step 8: Primer
Step 9: Base coat
Step 10: Clear Coat
Step 11: Profit?

Of you want a long lasting job, the rust areas need to be cut out in their entirety and new metal welded or brazed in or the panels in question need to be replaced. Otherwise, you will be revisiting them again. I guarantee also, that if you have rust in these areas, you have rust in others. I would not put much finish work time into a bondo job. It’s temporary and in some states, it won’t pass inspection if in critical areas. Don’t need to poke holes in your plan…they have been already and will continue. ;=\

If you do it properly or replace, you can make your car rust free in any area you live for a lot less effort then the work you put in now. It does require a regular basic body maintenance plan that your car up to now, hasn’t had.

Dump it and start over if you can afford to for your safety and the betterment of the auto industry profitablity. That was their intent anyway in making a car that suseptable to rust.

If you’re going to keep driving it in the winter, the rust will come back, probably within a couple of years. Once rust starts, if you bother restoring it, it should be on a car that’s summer-only. Otherwise, don’t bother.

The areas damaged arent structural or anything like that. Additionally bondo is not an issue in Illinois. Oh yeah, and I’m not really worrying myself about resale value here either, and I lack the tools and skills to weld in a new pannel. The guy that I know that could do it I’d rather not bother. That, and for the reasons listed elsewhere here I don’t feel bad about the bondo part.

I know that rust can be prevented, and will most likely return, but making sure the car never has rust again isn’t my concern.

Perhaps I should be more to the point. This is an old BMW. My goal is to make the car generally rust-free in appearance for about two years. I actually have the good fortune to be able to clean it after snowfalls and the such, so I think I can take the minimum precautions to stop rust from reforming.

So I guess that’s the next question. Even with the (I think) fairly rigorous approach I mentioned above, you all seem to believe the rust will return? Ok, how long will it take? If I do a full body sand treat, and paint, how long do I have?

Also, who has experience with rust converters? Do they work? Is there a particular one that works better?

After battling rust under my front wheel well for years in my 89 Mercedes, I found a good front quarter-panel from a U-Pull-It salvage yard for $30. It’s easy to bolt on. Not quite so easy to match the paint color.

Actually your plan is a good one. The rust converter is a phosphoric acid that converts the iron molecules on the surface to iron phosphide. This looks like rust but it protects the steel underneath. Some people think this also serves as a primer, but it doesn’t. Unfortunately, in the drying process, the coating develops micro cracks so it needs an additional sealer.

For primer, which will seal the micro cracks in the conversion coating, I recommend that you use a zinc chromate primer. You should be able to get some at an industrial supply store or NAPA.

Yes, it will rust again. A project like this just sets back the rust clock. It won’t set it all the way back to the new condition, but it sets it back some. eventually you will lose the battle, but you can delay the inevitable for many years.

Yeah, welding in panels to replace the rust is the best, but I undderstand what you are trying to do. First off, rust converter is worthless so save your money. Dupont makes an acid etching liquid that removes rust that will help. Also, grinding rust will overlay metal on top of the rust so you can’t get at it. Bondo is porous and will absorb moisture and promote rust. POR-15 is about the only product that even comes close to covering up rust and slowing it down but wear gloves and folllow directions. After cutting and grinding away the surface. Treat it with POR-15. Then use fiberglass with the cloth, or the heavier bodied fiberglass depending on how bad it is. Then you can bondo over that (but I don’t like the Bondo brand so use Everclear or 3M). Prime and paint.

Golding, may look into that on the front actually, but on the rear things aren’t so easy. Matching paint won’t be an issue though since I’ll be painting the whole car. I still don’t know why BMW ever made a car that was any color other than black.

Btw, sounds like zinc chromate primer it is.

I usually weld new panels in as well but that’s usually for restoration. In this case, the method of stopping the rust and patching it will hold up for a couple of years.

If you use POR, before you put on rubber gloves, rub some olive oil on your hands.
Those gloves will invariably tear and it will make the POR easier to remove from your fingers.
If you have pin holes, Rustbullet actually does a better job filling and sealing them.

On the inside of wheelwells, I’ve had good success using fluid film, spraying that over the job when done.
It keeps the moisture out and will stay tacky.

I think that your plan to address the rust is fine . . . but the car still is 27 years old. If it were my car I would treat the rust areas as you stated and then put the car on an “oiling” schedule. Like do it in the late Fall (November) and then again in the Spring (May). Oiling? Take your old motor oil and spray it into or onto the area where your found (and fixed) the rust, and other critical areas where you’ve seen rust on this model. where the rust occurs on this BMW . . . then oil those areas. SAAB used to have it in their maintenance schedule and it’s easy to do. A little messy for the day of application? Yep. Betcha the rust won’t come back . . . ever. Rocketman

The rust converters come in 2 styles. One you can apply as liberally as you want, and works fine. The other will leave a coating that has to be sanded off as it is like a paint.

"My goal is to make the car generally rust-free in appearance for about two years. " that would have been worthwhile info from the beginning.

“rocketman” describes just what I have done for many years to my cars in the rust belt…it’s easy and requires only treatments once a year, every other year to ensure treated areas NEVER rust. IT WORKS.

Always remember the rule when it comes to rust. What you see on the outside is only 30% of the rust that is actually there.


I bought a used '70 Mercedes SL with surface rust along the floor of the trunk, and used Eastwood rust remover and then sealer (you can find them on the web) after thoroughly removing all paint and primer down to the metal (I used the clear Eastwood sealer material so I could see if any rust returned). That area remained rust free for 10 years. We also avoided driving the car in the wet.

Fender wells and headlight areas were impossible to strip so I used one of the Eastwood products to “transform” or “seal in” the rust, and had no perforations over the same 10 years.

For the engine compartment seams and areas where no rust had formed, I used rocketman’s oil trick, although I used automatic transmission fluid instead of motor oil.

On the SL, I also made sure I removed as much of the factory-placed plastic rustproofing material as I could from the fender and frame areas. It just looked like it was no longer bonding very well and was probably causing more trouble than it was preventing.

On our old BMW, the drain holes in the rocker panels were small and easy to clog so I drilled them out and sealed the fresh metal.

I know what you mean about rust and older cars. Our SL, and a '71 BMW 2002 we bought new, seemed almost designed to trap rust inside the fender areas. Engineered Like No Other, you bet, and like most German cars, they are engineered to need expensive maintenance. After we needed to replace one fender on the 2002, I figured I’d need to keep the slush from getting thrown into the back and forward fender wells. I bought some thick plastic garbage bag condensers, made a heavy paper outline template of the fender well behind and in front of the tires, and cut the garbage bag condensers to fit. I then bolted them to in to keep out the heavy moisture, and it did work (we kept the car another eight years).

Good luck!

"satisficer " excellent account of the work that really needs to be done to preserve the body of cars. That work is well within the abilities of every car owner and does more to maintain the value of a car then changing the oil too often.

I use motor oil for inside panel seams and red grease for exposed components including nuts, bolts and frame members underneath that I want to preserve. I never used transmission fluid, though it think it would flow and protect as well as anything.

You are right, a car can’t have too many well placed drain holes. An often neglected area of an older car is the moisture we bring in under foot. A simple fix is custom floor mats that hold water and allow you to dump it out later; like those made by Husky.

I don’t consider any of these preservation methods tricks. I look at them as a way of paying myself several hundred dollars an hour, preserving the value of a car which is often at least as dependent upon body condition as mechanics. Why people have such a cavalier attitude towards rust, and accept it as inevitable while lying awake worrying if their last oil change might have been a hundred miles too late, is well beyond me. Good to meet others who get it.

Thank you again for all the suggestions everyone. I hadn’t heard of the “oiling” trick, but I will assuredly try it.

@dagosa: sorry if I didn’t make that quite clear from the start. I was trying to but didn’t exactly word it right. That’s what I meant when I said I’m going for “doesn’t that look nice for a car of it’s age” rather than “show car.” The floor mat thing, I’ve been using these deep well heavy rubber floor mats for year. Every car I buy, even the brand new one I bought, the first thing I do on the way home is buy a set and throw the carpet ones in the trunk. In my opinion, there is no reason to ever put a carpet floor mat in a car in central Illinois between dirt, rain, and snow.

@satisficer: I think I’ll try the eastwood products you recommend as well as pay close attention to the areas you mentioned. That POR product sounds robust, but a little scary to me. I’m going to be all over every system in this car so as much as I can minimize really nasty chemicals I’ll do that.

@Tester: I’ve heard that, so I’ll be doing quite a bit of sanding and grinding.

Thanks again for the suggestions everyone. I shall be most thorough with my treatments and cleaning. Just out of curiosity though, since the oiling thing does sound a little like a pain, would there be a benefit to thoroughly cleaning and working on the rust on the underside of the car (which amazingly isn’t bad actually, why is it that the pretty parts always seem to rust the worst first?) and spraying a rust preventing paint down there? Just thinking maybe it would help hold it back.

The oiling is not that much of a problem, if you have one or two oil cans of different sizes and nozzle lengths, and maybe you can get a neighborhood kid to do it once you show him/her how much fun it is (haha). One suggestion, now that I think of it – use a disposable drop cloth and some newspapers beneath the car and leave it there for a day or two. This will keep the oil from getting onto the floor (may save you from a fall) or the ground (and then into the water system) and may help do your inconsequential part to save the environment. You don’t need much oil and it is probably a very small part of the oil that gets used in this country anyway. Come to think of it, I would also try to use no-slip shoes or some kitty litter, and maybe put a little oil on any exposed cables you find. Body repairs are very expensive, at best.
Good luck!

Rust Never Sleeps

I always put used oil on rusty vehicles when i lived in wisconsin but i was never restoring. I would even go as far as to put diluted used oil (diluted with a little diesel) and spray the under carriage. Ive seen toyotas that had lots of miles left in them but the frame was rusted right through. Usually at the real spring shackles

Por 16 is good but expensive and if you get it on your hands, you can’t take your wife out to eat for a week. It dries hard like resin and it will get hard in the can shelf life 8-12 months then can’t get the lid off. I’ve had good results with “rust destroyer/ converter zinc chromate primers . Fiberglass must overlap 3” or more on clean metal…but moisture eventually gets in between metal and glass after 2yrs or so…maybe pop rivets with pieces of sheet metal?