At What Level of Water Is a Car Considered Flooded & Ruined?

According to the Internet website Fraud Guides, up to a half million cars were flooded by Hurricane Katrina. Having been written off as total losses by insurance companies, many of these were shipped to other areas for sale; consumers are far less likely to suspect a “bargain” on a sales lot in the north or the west was a flood car from an area hit by a hurricane or other natural disaster. The rule that “you get what you pay for” is almost always applicable; vehicles priced way below book value seldom transpire to be the bargains they at first appear. Vehicle history reports should indicate if a car has been written off.

While the seals around car doors are typically well-designed and effectively draft-proof, they are not intended to resist standing water for long periods. If a vehicle has been immersed in ponded or running water that reaches a level higher than the bottom of its doors, incursion is possible. Sand, grit and silt are difficult to entirely remove from the carpets, particularly under seats; if a car is for sale with conspicuous amount of air freshener scent present, this can be a sign that the musty smell of mold and dampness is being covered up. Upholstery and door panels can be discolored below the line of the floodwater. Metal parts can be more prone to future rusting.

Water that enters a car’s electrical system can cause both immediate and eventual catastrophic damage. The starter motor is typically the lowest electrical device on a vehicle. While a ruined starter motor can be costly, on its own it is seldom reason to consider a vehicle written off. If, however, water is sufficiently deep that electrical and electronic components are submerged or simply splashed by waves of water created by the car’s motion, this can result in severe problems. Repair bills can be in the thousands of dollars, and even after all the sensors and control modules have been replaced the vehicle may still be prone to apparently random failures.

Most important are the car’s safety features. In modern cars, these rely on a complex interplay of information shared between an array of sensors, decision-making on-board computer chips and electrically-operated actuation devices. Damage to these components may well go entirely unnoticed until they are needed, at which point their failure can be extremely dangerous.

While historically the air intakes on car engines have been located toward the top of the engine bay, many modern car designers have moved the entry lower and closer to the front grille. The logic behind this change is that an air intake situated in a high pressure area creates a semblance of forced induction, making a little extra power available at higher speeds. An unfortunate byproduct of this relocation is that such designs make water ingression more likely under less extreme circumstances; fording a relatively shallow expanse of water, for instance.

Water is incompressible. If drawn into the cylinders while the engine is running, the pistons on the upward -- compression -- stroke will slam into an immoveable object. This can result in engine hydrolock, damage to the piston and piston rod, damage to the valves and the cylinder head and can blow the head gasket.

Water can enter the tailpipe of the exhaust-muffler system. This happens more readily in a non-running car, but if back-pressure is sufficient it can also happen when the engine is operating. Because of the height of most manifolds, water entering the tailpipe is unlikely to find its way into the engine. It could, however, lay in the lowest parts of the mufflers and in downward-facing loops and bends in the exhaust pipes, potentially causing problems with starting and running. The heat of the exhaust gases is likely to evaporate trapped water but -- if the car is left unused after a flood -- corrosion problems could eventually occur.

The pressurized nature of engine cooling systems allows the coolant to reach temperatures considerably above water’s normal boiling and evaporation point. For this reason, parts of a running engine are also extremely hot. When super-heated metal comes into contact with cold water, it loses some of its strength. A hot engine block sluiced with cold water could be weakened; even if no problems are immediately apparent, cracks could occur later that otherwise would not. Even cracks that are invisible to the naked eye can stress vulnerable components such as gaskets, causing secondary problems.

If water has crept up past the mid-level of the tires, it could be considered a total loss. When water has reached above the level at which electrical and electronic components are exposed, the car may be impossible or unsafe to operate.