A vehicle’s engine can fail in many ways, but hydrolock is one of the most disastrous. Hydrolock, though rare, can significantly damage or even destroy an engine by flooding its cylinders.
While most drivers will likely never experience true hydrolock, it is still useful to understand the symptoms, causes, damage, and repair if you encounter this circumstance yourself.
What is a Hydrolocked Engine?
“Hydrolocked” describes an engine when any internal movement is stopped due to fluid on top of one or more pistons.
Because fluids are mostly incompressible, the fluid, in this case, the piston in question, cannot complete its movement to the top of its stroke. In effect, the fluid “locks” the rotating assembly from continuing this rotational motion.
While an engine “hydrolocks, most often due to water being accidentally introduced to the engine’s cylinders, coolant, as a consequence of being in the middle of another mechanical situation, could also lead to a hydrolock condition.
Hydrolocking can happen in both running and resting engines, depending on the scenario. If an engine then begins to hydrolock, the engine will stall and likely damage various internal components due to the sudden shock.
Conversely, if the hydrolocked engine is in its resting state, there is little merit in trying to start it.
What Damage is Done in the Event of Hydrolock?
When an engine undergoes hydrolocking, it is typical for some type of internal component to sustain damage of some kind. However, in some rare cases, an engine is capable of hydrolocking without damage occurring.
As a general rule, the damage sustained while hydrolocking relates directly to the speed of an engine at the time of hydrolocking. The quicker an engine is moving, the more destructive the outcome of hydrolocking is likely to be.
Any observed damage while an engine is hydrolocking occurs as a result of the rapid stopping of mechanical components that were in motion just moments prior.
The momentum of an engine’s rotating assembly is usually absorbed by one of the weakest related components when the assembly stops moving. This is often enough to bend or destroy the associated components.
Below are some of the most common types of damage observed during hydrolock.
- Bent or broken connecting rods
- Ejected piston/connecting rod
- Cracked cylinder head
- Cracked cylinder wall
- Damaged crankshaft
- Bad bearings
Symptoms of a Hydrolocked Engine
The symptoms associated with hydrolock vary, depending on the precise operating conditions of an engine, and when they arise. Some of these symptoms, however, are more common than others.
Below are a few of the most common symptoms of hydrolock in engines.
- Sudden engine stall
- Abnormal sputtering
- Sudden “thump” noise when attempting to start the engine
- Failure of the engine to turn over
- Onset of knocking or hammering noise
Causes of a Hydrolocked Engine
#1. Water.
In addition to more extreme conditions of flooding, both fresh water and salt water intrusion also cause hydrolock.
The majority of freshwater flood damage occurs when the intake manifold allows water into the piston/cylinder space. The entry of water is more pronounced in vehicles equipped with a cold air intake; a cold air intake has a more open air inlet, unlike vehicles with enclosed filter housings.
A vehicle with a cold air intake will not only allow water entry more easily than standard air intakes, but it is also capable of hydrolocking a vehicle with a moderate amount of water if just the air intake is surrounded with water.
In many instances, water can intrude into an engine that is being operated or stationary, but damage is invariably much worse if this happens when the engine is at full speed and operating.
If possible, once a hydrolock incident happens, the engine should not be started until water can be manually expelled.
#2. Coolant.
Another form of a hydrolock condition is the result of coolant entering the cylinder and/or cylinders due to a separate mechanical malfunction.
Typically head gasket failures, but other mechanical failures that allow the coolant in a vehicle’s water jackets enter into the combustion chambers mostly make the scenario worse depending on whether coolant being displaced will collect in a cylinder while the engine is not running, if so this presents the greatest danger if it is allowed to collect while the engine is not running.
Given that the affected cylinder does not fill a cylinder to capacity, the piston/connecting rod in that cylinder has sufficient upward movement until the muck has filled the bottom of the cylinder head.
In many cases, the momentum attained by a piston in a solid state can be enough before hydrolock to cause a significant amount of damage to the insides of an engine.
Can You Repair a Hydrolocked Engine?
Whether or not you can repair a hydrolocked engine is mainly determined by a few factors, including the operating condition of the motor when hydrolocking initially occurred, the number of cylinders affected, and the extent of the damage suffered during hydrolocking.
For a severely damaged engine (for example, an engine with a blown piston/connecting rod through the oil pan or block), the chances of repair are slim.
This is also generally true for severely distorted pistons or connecting rods that have led to severe cylinder wall damage.
On the other end of the spectrum, it is greatly possible to fix an engine that simply “locked” when water causes a momentary hydrolock, without any internal damage.
Normally, this is accomplished by removing every spark plug and cranking the engine over, where the water will exit out of these holes, while effectively fixing the hydrolock issue.
Lastly, you will want to define the source of the fluid intrusion to avoid future hydrolock scenarios. In the case of a flood vehicle, this is pretty self-evident.
However, when the coolant causes a hydrolock, you will need to do further investigation.
When this occurs, you will want to fix any mechanical issues creating the fluid intrusion before returning the vehicle to service.
In these scenarios, this is typically the head gaskets on the engine, but pressure testing should be done to ensure a cracked engine block or cylinder head is not present.
Ways to Prevent Hydrolock
Hydrolock is avoidable if you take the right precautions when driving. Some ways you can protect your engine from accumulated liquid include:
Avoid High Water
Driving through floods or any form of high water is the number one cause of hydrolocks. If you come to a situation and there is water in front of you, slow down and take an assessment of whether it is safe to drive through it.
Consider finding a different route or stopping to prevent excess moisture into your engine.
Don’t Park Outside During Heavy Rain
Likewise, don’t park outside in heavy rain or storms that could potentially cause floods. Even if it isn’t raining, water could leak in naturally.
If you are washing your vehicle, don’t spray any water in the air filter area. Because of its structure and location, any form of liquid near that area will work its way into the engine or other important components.
Take Your Vehicle to Mechanics for Regular Maintenance
When the engine is close to hydrolocking, experts can diagnose and prevent hydrolocking. In the case of hydrolocking, the mechanics can also prevent further damage.
How Can Mechanics Restore a Hydrolock?
When hydrolocking occurs, a mechanic must first drain the water that has infiltrated the engine. If you take your hydrolocked vehicle to a mechanic, here’s what to expect during the repair. The procedure includes these essential steps:
- Step 1: The water or fluid inside the engine cylinders would be removed.
- Step 2: The engine would be taken apart and removed from the other assembly.
- Step 3: The engine-related parts, such as the bearing, pistons, and cylinders, would be inspected.
- Step 4: Parts that are damaged would be replaced.
- Step 5: Your car will be assembled and run to determine if a functional engine has been established.
How Much Does it Cost to Repair a Hydrolock?
To fully repair a hydrolock engine, prices could range anywhere from $3,000 to $8,000 for repairs. The exact amount will be dependent on the amount of damage to the engine and any other damage to components.