Faced with the common sight in Ireland at present of a flooded road the inclination of many drivers is to say, "I will take the chance.” They will drive into the water, often not really knowing how deep it is and hope for the best. But what they are doing is risking an awful lot more than just the car stopping and ending up with wet feet. They are also opening up the very serious possibility of catastrophic damage to the vehicle which can be both very difficult and very expensive to put right.

Keith Walsh, Lead Trainer at the MKW Motors Bosch Automotive Training Centre says there are two main problems that can be caused by driving in a flood, serious engine damage and major electrical faults.  

Keith explains, "When a car enters a flood when driving there is a very real possibility that the water may enter the engine through the air intake system. This depends on the position of the air intake, its height and the water level. Some cars have a very low intake down behind the bumper or behind the wing liner and these are very vulnerable.” In these cases the water can be taken in by the natural suction created by the engine’s pumping effect. This is highly likely to see the water end up in the combustion chamber. Here when the piston moves up to its compression stroke it would normally squash the air and fuel before ignition. The problem is when the water enters the cylinder and the piston moves to its compression position the piston will be stopped from moving, because unlike air water is not compressible so the piston action will be halted.

Keith says this can cause serious engine problems. "The crankshaft which mechanically drives the piston moving at thousands of times per second will keep going and as a result the forces generated from the piston’s sudden stop will have to be absorbed somewhere. The sudden stop forces will cause the piston con rod, (which is the drive linkage between the piston and crankshaft) to bend and this will result in catastrophic damage to the internals of the engine which will be very time consuming and costly to repair.”

The second major area of concern when it comes to flood damage is the vehicle electrical system. When a car stops in water there is a strong possibility that water will enter the passenger compartment and this opens up the possibility of much potential damage. Keith says, "Many cars now have electronic control units mounted in the floor of the vehicle and in the centre console. If these become submerged, the water ingress will result in immediate damage.” He adds, "Water is conductive to electricity so it will short all the internal components of the control units effectively destroying them.” ECUs can of course be very expensive to replace, but the water can also cause other longer term problems. "Once a car is back on the road, the presence of moisture on wiring and electrical connectors together with the flow of electricity will cause corrosion,” say Keith. He adds, "Over time this corrosion will grow and will begin to effect signals and current flow in the vehicle. This can cause instrument and system operation faults which will be extremely hard to diagnose and costly to fix.”

Motorist be warned the next time you see a flood on the road think about the potential heartache and misery of serious flood damage. Maybe it really isn’t worth taking that chance.