We know that our cars were treated at the factory with a vat of magic dip to help prevent rust, and the stuff works pretty well. In fact, that process is rumored to have started with the 1976 924 models – another Porsche “pioneering” box to check with our cars. Whatever it is, this process has worked to provide us with relatively rust-free cars after some 30-40 years.
Rust does happen, though, and keeping ahead of rust damage means inspecting parts of the car that you cannot easily see. They do rust in some places and in some environments, so knowing what to look for is important – especially if you are looking at one to purchase.
The first place to look is the battery box under the hood. Because of some electrical magic that occurs with electrical fields and metal, the places where batteries live tend to rust with little or no outside help. Since it is located at the bottom of the windshield, water is also something that can collect there when you also inject leaves and other debris that can clog the drain hole.
Repairs for this rust issue sometimes include layering fiberglass mat and resin; layering metal, fiberglass mat and resin; commercially-available leak stoppers; and other sometimes original fixes. Rarely will you find a repair that welds in metal to replace what is rusted…few take the time, effort and expertise needed to do that.
So when you check for battery box rust, you should remove the battery to look underneath it. It will either 1) show no rust with clean factory metal, 2) show evidence of rust repair or 3) show that rust is evident with little or no attempt to repair it. The extent of the rust will dictate your next move – it HAS TO BE REPAIRED! The battery box is directly over the passenger footwell, over the AC hardware, and near the AC electrical on the right kick panel. Water leaking in will leak into the interior. If the rust is bad enough – creeping up the sides of the battery box or showing large holes – then walking away from it may be prudent.
Next look at the passenger floor for evidence of leakage. If the battery box has been leaking, the carpet may damp or even wet. There may be mold, discoloring, or the jute padding under the carpet may be damp, wet or in poor condition due to the moisture. The floor may also show signs of rust under the carpet. While you are there, check the rear seat floor for evidence of wet or damp conditions – the water sometimes will run under the seat and collect in the rear floor.
If the battery box is okay, then you look elsewhere for evidence of rust and rust repair. Bubbling paint can be a tell-tale sign of rust developing or a poor rust repair. The fenderwells, in the wheel arches, and behind the front wheels between the fender and the inner body are places where debris can gather, hold moisture and in northern climates road salt, thus causing rust issues. The old “magnet checking for Bondo” is also a good way to check these areas for previous repairs. If the magnet doesn’t stick, there is filler present.
Once you are satisfied that the body is in good shape, the next place to check is underneath the car. Look at the metal lines for fuel and brakes that run the length of the car. A northern car that has been driven on salted roads in the winter can gather the ingredients for rust and eat these lines. Fuel and brake lines that show flaky rust on the surface are near failure and must be replaced. (A recent purchase of a north-eastern 924S had the high-pressure side fuel line repaired with a piece of rubber hose and two hose clamps. Under the car. Next to the catalytic converter. Not good!) Replacing these lines is NOT for the faint of heart, and requires special skills and special tools.
Also look at the brake calipers for rust accumulation. We have seen the calipers on cars that have not been driven for a time actually rust solid. Look at the hardware that holds the pads in the caliper – if the pins and springs are rusted, you may not be able to change the pads. If you can get the pads out, you may have to purchase new hardware for over $50 per axle. A pricey repair. And there is seemingly a shortage of replacement rebuilt calipers.
While you’re looking under the carpet on the passenger side for moisture or water, also look at the back floor area behind the front seat. Look for noticeable rust on the seat slider and base in the back. If the seat will not easily move back and forth, there may be rust on the seat tracks – or something is bent – or both.
Look inside the rear hatch at the spare tire well and the two areas behind the rear wheels on each side for rust and/or accumulated water. Look for signs that water has been sitting there, and make sure that the drain lines from the hatch latches and the sunroof drains are still there doing their jobs.
Our cars were treated at the factory for rust, and that treatment has held up quite nicely. However, some cars were repaired from crash damage with the treatment sanded off the body completely, making those areas prone to rust.
Fixing body rust can be an expensive proposition as there is a body shop labor rate AND a respray needed to fix the damage. Finding a good, solid rust-free car with decent paint is a MUST when looking for a car.