Hydrolocked Engine – What Is It – What Damage Can It Do

When an engine is seized from ingesting a substantial amount of liquid it is said to be hydrolocked.

With all internal combustion engines, the internals are all designed to deal with the compression of air.

Hydrolocked Engine
Hydrolocked Engine

However, Liquid is non-compressible and when ingested into the cylinders it is said to be hydrolocked.

The amount of damage from a hydrolocked engine depends on engine speed when the liquid was ingested.

Also, The amount, type of liquid and how it got in will have a major effect on what happens.

So, When your engine first encounters a bit of extra liquid in the cylinders, your engine will begin to misfire.

However, If it’s just a small amount of liquid, it might just blow right out the exhaust.

While, If more liquid is drawn in, you’ll hear a loud knocking noise as the cylinders fill up.

It could be just a second or two, and then your engine will shut off with a thud.

Causes Of A Hydrolocked Engine

Flood Damage
Flood Damage

By and large, the most common cause of a hydrolocked engine is water entering the air intake. More specifically, a cold air intake system that is immersed in water is the typical cause. Water can enter the intake on any engine, whether it’s from driving through water or an actual flood. Engine coolant can enter the cylinders when a head gasket blows. A failure in the carburetor or injectors can introduce liquid gasoline or diesel into the cylinders.

Damage From A Hydrolocked Engine

Big Leak, Fast Engine Speed

The real damage occurs when a large volume of liquid makes its way into the cylinders.


Also, With higher engine speed comes more engine damage. ( Almost sounds like a quote from Spiderman )


Bent Rods
Bent Rods

The reaction forces involved will almost certainly break internal components:

  • Piston Damage
  • Cylinder Walls Crack
  • Connecting Rods Bend
  • Connecting Rods Snap & Go through the oil pan
  • Damage to the cooling system
  • Cold Water Shock to Hot Engine
  • Head Gasket Failure
  • Catalytic Converter Damage
  • Rod/Main Bearing Wash out
  • Crankshaft Damage

Again, The amount of liquid ingested and where it came from will reflect the amount of damage.

Small Leak, Slow Engine Speed

Amounts of liquid significant enough to cause hydrolock tend to upset the air/fuel mixture in gasoline engines. This result could make the engine stall. So, If hydrolock actually occurs it does not cause catastrophic engine damage. If an engine hydrolocks at idle speed, it may simply stop and refuse to turn over with the starter motor.
There may well be no internal component damage. You may be able to correct this by removing the spark plugs or injectors. Next, Turn the engine over using the starter motor. This will help expel the liquid from the cylinder or cylinders. Once reassembled, the engine should start as normal.

The hydrolocked engine 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 repaired.


Blown Head Gasket
Blown Head Gasket

Furthermore, Coolant is corrosive to the internal parts of an engine. When you leave this standing for any length of time, the damage will only get worse. Remember engine coolant eats bearing material.

Trying to restart the engine will only cause further damage. You may cause damage to parts that were actually ok:

  • Starter
  • Flywheel
  • Transmission
  • Cause A Head Gasket Leak
  • Engine Block
  • Transmission Housing
  • Connecting Rods
  • Pistons

Consequently, A hydrolocked engine can also occur when the engine is not running. It’s the case with flood cars, for example. Fluid fills the cylinders while the engine is not running and the starter can’t crank the engine over.

Hydrolocked Engine-Conclusion

The most disconcerting aspect of a hydrolocked engine is that it can strike without warning. Regular maintenance and inspections are the best way to keep on top of this issue. Preventative maintenance is a lot cheaper and much safer than a hydrolocked engine.

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About Danny Bender 180 Articles
I have been into cars for as long as I can remember but the engine is what interested me the most. Now with over 40 years in the engine rebuilding and machine shop industry I have retired. I will be spending my time sharing what I have learned while keeping up with the latest Technology - Helping Solve Engine Problems !