A friend in the Car Talk Communities asked a great question last week as he was about to purchase a used car:
I am considering purchasing a used car, 2008 Chrysler Town & Country (58K miles).
But I saw some rusted part in the engine room. I attached two pictures below:
It’s a great question. Rust is insidious. Depending on what the weather’s like where you live, whether you live near the coast, or whether your municipalities spread salt on the road when it snows, rust can be a show-stopper when purchasing a used car.
We’ll start by answering hyukpyohong’s question about rust in the engine bay, and then move around the car to find critical areas where rust can form.
The rust in question in the two photos above is very light surface rust on both the alternator and the exhaust manifold. It’s normal, and neither condition is going to cause any problems with the function of those two parts.
The alternator has oxidation on both the cast aluminum housing and the steel stator core, but neither of those would cause any major problems. Plus, the alternator is an easily replaceable part, so there’s really no harm here.
Exhaust manifolds like the one in this Town & Country are cast iron, and they’re prone to rust almost from the minute they leave the factory. They’re untreated, and to add insult to injury, they’re subjected to heat cycles that go from sub-zero to 1000 degrees within a half an hour. The manifold shown in the picture has a fair amount of surface rust, but it looks like the bolt heads are still in decent shape.
Rust on the manifolds themselves isn’t really the issue, it’s rust on the bolts that secure them to the head and to the exhaust downpipe that can cause all kinds of problems. I recently replaced exhaust manifolds on my 1978 Blazer and the manifold bolts were so corroded that I ended up having to drill and tap the holes on two of the bolts that held the manifold to the head. The studs that held the downpipe were rusted to the diameter of a toothpick. Replacing rusty bolts and studs can be done, but it is one of the more unpleasant, time-consuming jobs you’re likely to encounter.
Engine parts will typically get a layer of surface rust, but that’s becoming less and less common as plastic replaces steel under the hood. The big rust concern is in the strut towers. Manufacturers are getting more and more sophisticated with their rust prevention methods, but it can still occur. When a strut tower gets rusty, unless it’s a classic car you’re emotionally attached to, it’s probably time for the crusher.
Check with our friends over at Car Complaints to find out if rust is an issue in the car you’re inspecting. The photo above comes from their database of complaints on a 2000 Dodge Caravan. When rot like this appears, the strut’s top end is essentially connected to nothing but air, and it’s a major safety concern. Walk away from a car that has rust like this in either the front or rear strut towers.
Rust in the doors typically starts because the drain holes in the bottoms of the doors haven’t been cleaned out periodically. Dirt and leaves sit wet inside the door cavity and rust eventually pokes a hole in the sheetmetal.
Rust in the doors is cosmetically lousy, and it probably indicates that there’s rust elsewhere, but since doors are relatively easy to replace — even for a backyard mechanic — and replacement doors are pretty easy to source, it may not be a deal-breaker.
Just get a good look at the rest of the car and keep your distance if several other areas are rusted out.
You don’t see rusty fenders the way you used to. In the 1970s, every car in the Northeast had whole sections of wheelarch missing.
There are two parts that make up the complete fender: the inner fender and the outer fender. Most modern cars have plastic inner fenders that are immune to rust, but if it’s an older car, keep an eye out for rust here.
The outer fender — the part you see — typically rusts where two or more pieces of sheetmetal are joined, either by a weld or a bolt. The wheelarch itself can rust out, and so can the bottom of the fender. Leaves and gunk get caught between the two fenders and can cause rust if it’s not cleaned out regularly.
Front fenders typically bolt in place, so replacing one isn’t such a big deal. Rear fenders require a lot more work to repair. If you’re looking at a fairly common vehicle, you can often find nice patch panels that a body shop can use after they’ve cut out the rust, but less common cars need more work, and as a result, more expense.
Unless you’re looking at something really unique that you have to have, rust in the rocker panel area should be a dealbreaker.
Whether you’re considering an older, body-on-frame car or a modern unibody car, the rocker panel area is critical to the car’s structure. In body-on-frame cars, cutting out a rocker panel requires a ton of work, up to and including bracing the door opening so that the entire body doesn’t collapse. On a unibody car, the rocker area is a stressed member of the car’s entire space frame. Fixing it correctly is probably more trouble than it’s worth.
The same advice for rocker panels holds true with floors. They’re a lot of work to replace, requiring the removal of the entire carpet. Rust on the floor can creep into the bulkhead, the firewall and the transmission tunnel.
Rot in the floors might seem like a problem for just old cars, but modern cars can be victims of the tinworm, too. Check out the complaints of completely rusted floors on the 2002 to 2006 Nissan Altima at CarComplaints.com, for example. That car in particular had major issues with catastrophic rust.
You should be able to see a rusty floor from underneath the car. If you suspect a rusty floor but can’t verify it from underneath, it’s worth pulling up the carpet to see it from inside the car. Look in the driver’s footwell, especially under the area where a driver’s heel would be grinding into the carpet for thousands of hours.
Also pay attention to the trunk floor. Leaky rear glass or tailgates can allow water to pool in the trunk floor and cause terminal rust.
Exhaust tubing is typically made of one of three materials: Cold-rolled steel, stainless steel or aluminum. Cold-rolled steel can rust out in a surprisingly short period of time. Stainless steel is less susceptible to rust, but it can still occur. Aluminum exhausts typically don’t corrode and will outlast both the car and the driver.
Look for rust in places where the tubing bends, where it’s joined to other sections of pipe or to mufflers and catalytic converters, or in the mufflers and converters themselves.
Replacing an exhaust can be expensive, but a rusty exhaust in a used car might not be a dealbreaker. It’s just an indication that the car hasn’t been cared for as well as you might like. Just get it done, because holes in the exhaust aren’t just unsightly and loud. Carbon monoxide can creep into the passenger cabin and cause headaches at best, and multiple fatalities at worst.
There are loads of metal parts that make up a suspension, from control arms to sway bars to shocks and struts. We’ll try to cover these areas in order, from least concerning to most:
Shocks and struts consist of a piston moving in and out of an oil- and gas-filled sheetmetal tube. The exterior of that tube can easily show areas of surface rust, and that’s not a concern. If it’s left for any length of time, that surface rust can blossom into full-blown rot, and that needs to be addressed. Shocks and struts are wear items, though, and replacing them isn’t terribly expensive.
Control arms in more expensive cars are generally made of cast aluminum, but in less expensive cars, they’ll be made of sheetmetal. They can rust out and cause catastrophic handling issues. Surface rust is ok, but any kind of perforation is a problem. These parts can be replaced, but you don’t want to be responsible for it when you’re buying a used car.
Suspension mounts — attachment points where the replaceable, moving suspension parts are bolted — can either be part of the body on a modern car, or part of the ladder frame on a pickup truck of any vintage, or an older car.
Like the strut towers we mentioned under the hood, if any of the areas where suspension parts meet the rest of the car are rusted, move on down the road and find another car. You don’t want to be involved in repairing that kind of catastrophic damage.
If your initial inspection turns up rust in any of these areas, it would be worth having a professional take a look at the rest of the car to find rust that isn’t readily apparent. A pre-purchase inspection is definitely a good idea. For around $200, having a qualified shop spend a few hours poking around the car can save you tens of thousands in the long run.