Hydrolock, properly called hydrostatic lock, is a failure in an internal combustion engine; the engine is prevented from turning over by fluid in the cylinder above the piston. The damage caused by hydrolock is dependent upon the state of the engine when it occurs; the results are different in a stored, non-running engine, an engine running at idle and an engine running at speed.
If an engine’s piston cannot complete its full travel cycle -- up to its minimum at the top of its stroke, then down to its maximum at the bottom of its stroke -- the engine cannot turn over. If the piston or pistons that cannot complete their travel cycle are prevented from doing so by a liquid above them, they slam to a halt on the upstroke, hence the “lock” in hydrolock. This condition occurs when fluid enters the top of the cylinder, rather than gas; gas is compressible and the piston can keep moving upward as it compresses, while fluid is not compressible and prevents the piston from reaching the top of its stroke. Water was called “hydro” in ancient Greek, hence the “hydro” in hydrolock.
Causes of Hydrolock
Outside water can enter the engine through the air intake if the vehicle is driven through a flood; vehicles designed with low-mounted air intakes can draw in water from a bow-wave caused by driving through relatively shallow standing water. Engine coolant can enter the cylinders when a head gasket blows. A failure in the carburetor or injector mechanisms can introduce liquid gasoline where only a vapor-air mixture should be.
What Gets Damaged
Although an engine that hydrolocks at idle may simply stop, catastrophic engine failure is likely if an engine hydrolocks while running at speed. The most common result of hydrolock at speed is that the piston rods are deformed; they bend and fold between the piston at their top, which cannot travel upward any farther, and the crankshaft at their base, which continues to travel upward. Absorbing the force of the sudden stop may crack the block, crack the crankcase, destroy the head and shatter the bearings.
Manifestations and Rectification
Typically, an engine will seize solid if it hydrolocks at speed. If only one piston hydrolocks and the engine continues to move, there will be a loud screeching noise. Given that most of the major internal components have been destroyed, replacing the engine is typically more cost-effective than rebuilding.
If an engine hydrolocks at idle, it may simply stop and refuse to turn on the starter motor. There may well be no internal component damage. Rectification is by removing the spark plugs or injectors then turning the engine on the starter motor; this will expel the liquid from the cylinder or cylinders. Once reassembled, the engine should start as normal. The hydrolock, however, was a symptom, not a cause. If the liquid was introduced to the cylinder through a failed component, typically the head gasket, this must be diagnosed and rectified. Further, water is corrosive to the internals of an engine. If water has been inside a standing engine for any length of time, it could have caused rust bands to form inside the cylinder. These would have to be addressed, and the pistons perhaps replaced.
- Photo Credit Wavebreakmedia Ltd/Wavebreak Media/Getty Images
The Parts of a Hydraulic Cylinder
Hydraulic cylinders generate linear force and motion from hydraulic fluid pressure. Most hydraulic cylinders are double acting in that the hydraulic pressure...
GM Diesel Engine Problems
A diesel engine is a type of internal combustion engine that uses compression-heat to burn the fuel sent to the combustion chamber....
Getting Rid of Water in a Motorcycle Gas Tank
Water can get into your motorcycle's gas tank in a number of ways, but the most common means is by condensation. If...
How to Avoid Hydrolock
Hydrolock is caused by water or other liquid entering the engine through the intake, where only air is supposed to go. Engines...
How to Settle a Car Insurance Claim Due to a Flood
Comprehensive coverage, or other than collision coverage, generally provides reimbursement for any damage sustained to an auto due to falling object, fire,...
My 2003 Pontiac Grand Prix Won't Start
There are a number of factors to take into consideration when trying to troubleshoot your 2003 Pontiac Grand Prix that when it...
How to Fix a Stuck Lawn Mower Engine
Pulling the cord on a lawn mower and having it not function can produce frustration, fear and anger. But with a little...
How to Stop Cold Air Intake From Hydrolocking
Hydrolocking occurs when water -- or any fluid -- is ingested by an engine. Since fluids do not compress in the same...
Installation of the Hydrolock Quick Connect
The Moen Hydrolock Quick Connect joins compatible water supply valves to flexible hoses and faucet spraying components. Hydrolock Quick Connects feature female...
My Drive Belt Is Making Screeching Noises
The alternator drive belt, also known as the fan belt, is an important part of your car's engine. The alternator drive belt...
Causes of Failure With a Connecting Rod
The connecting rod connects the pistons to the crankshaft. It converts the linear motion of the pistons to the rotary motion of...
Briggs & Stratton Valve Specs
Briggs and Stratton is one of the world's largest manufacturers of small gasoline-powered engines, most commonly used in lawn mowers, but also...