TOM: Since the two big hurricanes, we've had a flood (ha ha) of questions about flooded cars. So we thought we'd try to answer all of the most common questions at once:

Q: How do you know if a car you're buying has flood damage?

RAY: Well, there's the obvious stuff: Fish in the back seat. A lobster trap hanging off the headrest. A bathtub ring at the level of the inside door handles. You sit in the driver's seat and your butt gets wet.

TOM: Assuming none of those obvious signs is present, you might see mineral deposits or discoloration on the seats, seat belts or door panels. There might be droplets of moisture on the inside of the instrument cluster, warped or misshapen door panels (if they're made of fiberboard), or an owner's manual that looks like it fell into a bathtub.

RAY: In the trunk or engine compartment, you might find mud, sticks or other debris. And inside, a heavy aroma of Hai Karate aftershave or Lysol is a telltale sign that someone's trying to cover up a festering mold or odor problem.

TOM: But most likely, if a "professional" is trying to pass off a flooded car on the used-car market, he will have cleaned up all those things, and perhaps even replaced the seats and carpet. It will be very difficult for the average buyer -- or even the average mechanic -- to be able to tell that the car was flooded.

RAY: So, our best advice is to simply avoid used cars that have come from flooded areas. "Sure," you say. "How do I do that?" Well, the current title of the car provides no guarantee that the car is clean. Unfortunately, flooded and salvaged cars can be re-registered in other states with clean titles, and then sold without disclosing the damage. That's called title washing.

TOM: So, your best bet is to use a service called Car Fax. We've put up a link to it on our Web site, www.cartalk.com. It's now offering a free service that will check the ZIP code in which a car was last registered, and will let you know if it was registered in one of the flooded areas. You need the Vehicle Identification Number, or VIN, to get a report.

RAY: While it's not absolutely perfect (it's possible that someone with a car registered elsewhere could have driven to New Orleans and been there for the flood), that's about the best chance you have to spot a potentially flooded car before you buy it.

Q: Is a flooded car necessarily junk?

TOM: Pretty much, yes. There are some obvious problems, as you can imagine. If water gains access to one of the cylinders, either through the air intake or the exhaust system, that cylinder can fill with water. Then, when the engine is started, that cylinder will hydro-lock (water can't be compressed like air can), and everything connected to the cylinder will break or bend.

RAY: But even if the water is pushed out safely before the car is started, that cylinder has already had water sitting in it for a week. Those cylinder walls and rings are probably already rusting. So that engine's going to burn oil like crazy and run unevenly.

TOM: Water can get into the transmission through the transmission-fluid dipstick hole. If that happens, you'll be lubricating the transmission with one part transmission fluid and two parts water, or something like that. So kiss the transmission goodbye, too.

RAY: Inside the car, lots of manufacturers now put electronic components -- like computers -- under the seats, or under the dashboard. So even if only a modest amount of water was sloshing around the floor of the car, you might need a new computer -- or several new computers, depending on your car -- which can cost $1,000 each.

TOM: If the water gets a little higher up, it can wreak havoc on electronic seat controls, electric windows, ignition switches and air bags. More and more cars have seat-belt pre-tensioners now, which use pyrotechnic devices housed where the seat belt attaches to the bottom of the door pillar. Pucker up and kiss those goodbye, too.

RAY: And then there's the whole issue of mold. When a car is filled with water, and then closed up and baked in the sun for a week, you've got mold-spore heaven. That's not only a health hazard, it's nearly impossible to fix.

TOM: So, we'd say if water got any farther than the floor of the car, it's junk.

Q: What if I already own a car that's been flooded?

RAY: Time to look at the '06 Camrys. You have our sincere condolences. Your best bet is to have your insurance company declare it totaled and pay you for it. If you're not insured, and not in a position to replace it, you can try to keep driving it. But not before you perform some crucial tasks.

TOM: First, you have to get the water out of it. You have to remove and either clean or replace the seats, the carpet, the interior panels and possibly even the headliner. Bleach has to be used to attempt to kill the mold spores -- the sooner, the better.

RAY: You have to remove all the spark plugs and then turn the engine over to purge any water that might have gotten into the cylinders. If water comes out, that cylinder is a candidate for corrosion and failure. You also have to drain the motor oil and transmission fluid, in case water has gotten in and diluted those crucial lubricants.

TOM: Then you can start the car and start looking for electronic gremlins. And hope the mold and the smell don't get too bad.

RAY: So basically, if a car is flooded and it's your only transportation, you might be able to use it. But it's bound to cause you problems. Think about it. Insurance companies HATE to spend money. If they could fix a car and put it back on the road, theydo it in a New York minute. And even THEY won't bother fixing flooded cars.

TOM: So, if you absolutely have to keep a car that's been flooded, consider it a short-term solution. And if you're shopping for a car, buyer beware.