Courtesy of About.com http://cars.about.com/od/adviceforowners/a/What-To-Do-If-Your-Car-Is-In-A-Flood.htm
1. Do not attempt to start the car! It's tempting to turn the key and see if the car still works, but if there is water in the engine, attempting to start it could damage it beyond repair. I've outlined a few basic checks below, but if in doubt, its best to have the car towed to a mechanic.
2. Determine how deep the car was submerged. Mud and debris usually leave a waterline on the car, inside as well as out. If the water didn't rise above bottom of the doors, your car will probably be fine. Most insurance companies will consider the car totaled (damaged beyond economically-reasonable repair) if water reaches the bottom of the dashboard.
3. Call your insurance company. Flood damage is generally covered by comprehensive (fire and theft) insurance, so even if you don't have collision coverage, you may be covered for repairs or replacement. Your insurance company will probably be flooded (sorry) with claims, so it's a good idea to start the process early. (More about floods and car insurance.)
4. Start drying the interior. If water got inside the car, mold will grow quickly. Start by opening the doors and windows and putting towels on the floor to soak up water, but you should plan on replacing anything that got wet, including carpets, floor mats, door panels, seat padding and upholstery. Remember, these repairs are likely to be covered by your comprehensive insurance.
5. Check the oil and the air cleaner. If you see droplets of water on the dipstick or the level of the oil is high, or if the air filter has water in it, do not attempt to start the engine. Have it towed to a mechanic to have the water cleared and the fluids changed. (Hard-core do-it-yourselfers can try changing the oil then removing the spark plugs and cranking the engine to blow out the water, but we still recommend leaving this to a mechanic.)
6. Check all the other fluids. Fuel systems on late-model cars are usually sealed, but older cars may need to have their fuel systems drained. Brake, clutch, power steering and coolant reservoirs should be checked for contamination.
7. Check all of the electrical systems. If the engine looks OK to start, check everything electrical: Headlights, turn signals, air conditioning, stereo, power locks, windows and seats, even the interior lights. If you note anything even slightly amiss -- including the way the car runs or the transmission shifts -- that could be a sign of electrical trouble. Take the car to a mechanic, and remember that the damage may be covered by insurance.
8. Check around the wheels and tires. Before attempting to move the car, look for debris lodged around the wheels, brakes and underbody. (Set the parking brake before crawling around the wheels!)
9. If in doubt, push to have the car totalled. A flood-damaged car can experience problems months or even years after the event. If your car is a borderline case, consider pushing your insurance company to declare the car a total loss. Replacing it will cost money, but you may save yourself from some major (and expensive) headaches down the road.
10. Beware of flood-damaged replacements. Many cars that are totaled due to flooding are simply cleaned up and re-sold. Before buying a used car, have the title checked; words like "salvage" and "flood damage" are giant red flags. Get a comprehensive history on the car -- if the car has been moved from another state and re-titled (especially a state that has been subject to flooding just before the title change), the seller may be trying to hide flood damage.
According to the National Safety Council, if your car suddenly becomes submerged, stay calm and remain buckled in your seat. If the water is substantially deep, the car should remain afloat long enough for you to escape. Immediately unlock the doors and open the windows – your car’s power accessories should continue working for at least a minute or so. Unbuckle your seat belt (and those of children or other riders who need assistance) and exit through the open windows, swimming to safety in the direction of the current if you’re in deep water.
If they won’t open, try kicking out a side or rear window, though it won’t be easy. Those living in flood-prone areas might want to consider carrying a small hammer or specific car window-breaking tool in the glove compartment for this purpose. If you can’t leave via a window and water is entering the cabin wait until the pressure is equalized on both sides of the door (usually when its as deep inside as it is outside) before attempting to open it.
The AAA cautions that you not to try starting a car that’s been submerged without first having a technician perform a thorough inspection and cleaning. Salt water, for those who live in coastal areas, can be particularly damaging to a car’s components. Even if it starts up on the first try, Nielsen says a flooded car’s engine, transmission and fuel, brake, power steering and electrical systems are vulnerable to increased wear and premature failure.
If you’re calling the AAA or other service for roadside assistance, be patient, as you’ll probably be on a long list of those seeking help, and have reasonable expectations. The AAA generally handles dead battery/starting, flat tires, lockouts and other relatively minor service issues. Tow trucks are set up to drive through about 18 inches of water to pull submerged vehicles to dry land
If a car has been completely or partially submerged, extensive disassembly may be needed for a thorough cleaning. Unfortunately, this doesn’t come cheap. Depending on its make, model and age, the cost to restore a flood-damaged vehicle could exceed its value, in which case the owner’s insurance company would consider it "totaled."
Don't wait for the adjuster to arrive. Mold and corrosion are setting in now. You need to clean out as much liquid and mud as you can and dry out your car as soon as possible. Don't try to start the car. If there's water in the engine, transmission or fuel system, you'll just compound the damage. Disconnect the battery ground strap first-you must do this, otherwise you'll fry something. Next, begin assessing just how deep the water got. Frankly, if the waterline is as high as the dashboard, you will probably be better off talking the adjuster into totaling the car and getting another. Double that for salt water. The mechanical systems and the interior can be dried out or cleaned with a lot of labor, but the electrical systems on modern cars are extremely complex. These systems rely on a lot of low-voltage signals from sensors in the engine management system and ABS. These low-voltage signals are extremely sensitive to corrosion on connectors, and problems can crop up for years. Look for a high-water mark. That can be easy--if the water was muddy or there was a lot of floating grass and leaves. But clean water may leave no residue. Look for water inside the doors and the taillights, and dampness in the carpets and interior trim. This will allow you to eliminate cleaning some areas or systems on the car unnecessarily. Let's go through those systems. Check the dipsticks for the engine and transmission. If there are water droplets clinging to the end of either dipstick, you absolutely, positively need to change the oil and filter before even thinking about starting the engine. If the water was muddy, it's probably wisest to remove the oil pan from the engine and wash the mud out. Change the oil and filter again in a few hundred miles, too. Late-model cars have sealed fuel systems, and probably won't get any water in them. But that classic '55 T-Bird probably ingested some water if it was deep enough and lingered long enough. Siphon the fuel out into a container and look for water. If you find any, it's probably best to drop the tank and get it cleaned professionally. Blow out the fuel line, and you may need to get water out of the carburetor float bowls as well. If you find evidence of water in a fuel-injected car or truck's tank, replace the fuel filter as well. That paper element will disintegrate if it gets waterlogged. It's not that a few drops of clean water are bad, but floodwater is usually pretty foul with silt and sludge. Muddy water can infiltrate its way past engine seals within a few hours. Crankshaft seals, transmission seals and axle and CV joint seals are adequate to keep lubricants in, but they are not designed to keep standing water from creeping in. Before you start the engine, or tow a car with the wheels on the ground, drain and change the oil, transmission fluid and final-drive lube. Check the dipstick for water droplets. And don't forget wheel bearings and constant velocity joints, which will need to be cleaned and repacked. Some front-drive cars have sealed-for-life front axle bearings, and you'll simply have to wait for those to fail, because it's nearly impossible to clean and relube them. And then change those fluids again in a thousand miles or so if there was evidence of muddy water.