Driving a car through water is always a risky maneuver, and it may destroy the engine.
Hydrostatic lock, or hydrolock for short, occurs when a hydraulic cylinder attempts to compress a liquid. As every Chemistry I student knows, liquids are relatively incompressible—unstoppable force, meet immovable object.
Instead of causing an existential paradox, however, the engine is much more likely to destroy itself, often violently.
A car engine is designed to operate at several thousand RPM and withstand thousands of pounds of pressure at high heat, but in a single loud instant, the precision-crafted components within the engine will twist or shatter when they try to compress even less than two ounces of water.
This is most likely to happen when a car is driven through deep water.
“You push that big [wave] of water and when it gets in the intake, it’s all over,” said Justin Sims, a mechanic at Ice Cold Air on Fourth Street N in St. Petersburg.
In the shop was a bright red Pontiac Solstice, a little two-seater, ground-hugging roadster. To its side, the engine was attached to a stand and flipped upside-down. The mechanics removed the oil pan to show the twisted internal components.
The first point of failure in this case was the connecting rod, the I-beam that connects the crankshaft to the piston head. In other cases, hydrolock can crack the piston head, destroy the seals in the cylinder and even lodge metal shards into the engine block.
It’s often cheaper to just replace the engine than to try to replace the broken parts, said shop owner Paul Smith. A used motor for the Solstice will cost the owner, or the insurance company, $2,200.
It’s a lesson on “why not to drive your car through two feet of water,” said Jeremy “Doc J” Strait, another mechanic on duty. Some new cars pull air from below; depths as shallow as six inches can cause water to be sucked into the engine.
Cars move forward because they create combustion by combining oxygen, fuel and heat. Air is pulled into the engine through the intake on the front of the car. During the intake cycle of the engine, this air is pulled into the cylinder and mixed with fuel. This mixture is then compressed in the now-closed cylinder, thus increasing pressure and temperature, in accordance with the combined gas law.
The spark plug ignites the mixture, causing combustion. The rapid expansion of gasses pushes the piston downward, causes the crankshaft to rotate and ideally, the car to move forward.
If water gets into the air intake, however, the vacuum created during the intake cycle can pull that water into the cylinder, as if sucked through a straw. At that point, two ounces of water might as well be a slab of granite.
Driving through water carries other risks, as well. When brakes get wet, they have a harder time stopping the car, interiors can be flooded, and the car’s electrical systems can short. Water can leak into the wheel bearings, transmission or differential; and water can be sucked into the exhaust pipe, stalling the engine.
Photo by Christopher Guinn