What is a Hydrolocked engine? – Causes, Fixes & Preventions

Vehicle engines comprise several parts, one of which is the cylinders—where combustion takes place. However, only fuel and air are needed by the cylinder to carry out combustion. Should any other fluid enter in large amounts, it can cause a problem known as a hydrolocked engine.

But what exactly is a hydrolocked engine, and how does it happen? I will explain this in the next section. I will also cover how to prevent it, how to know your engine is hydrolocked, and possible fixes.

how to fix a hydrolocked engine

What is a hydrolocked engine, and how does it happen?

A hydrolocked engine is an engine that has seized due to the ingress of excess water in its cylinder. While water is not supposed to enter the cylinder, a small quantity won’t do much harm. However, when it gets too much, hydrolocking occurs. So how much water to hydrolock an engine? Typically, an amount larger than the volume of the cylinder is enough to do the mischief.

When too much water enters the cylinder, the rotation of the crankshaft will force the piston upward so it compresses the water. However, because the piston cannot compress water like fuel and air, the water inside the cylinder will cause the piston to cease moving. Invariably causing the engine to seize and rendering your car immovable.

Unfortunately, water isn’t the only liquid that can cause hydrolocking. Other fluids that can cause hydrolocking when they enter the cylinder include coolant and oil. Now that you know what causes hydrolocked engine, knowing how do these liquids get into the engine is the call of the time?

Hydrolocking can happen during a flood when a car gets completely submerged in water, causing the cylinders to get filled with water. Regularly driving through a high or large body of water can also result in hydrolock. Most cars have the beginning of their intake placed near the wheel, which can result in water covering the air intake, making its way into the air filter, and then the intake manifold.

Modification, which causes the air intake to be placed at a very low level so outside air can enter the engine, also results in hydrolocking. Some placed their cone air filters just below their bumper. If the water is even a little above the bumper, water will likely ingress. Water can also enter the engine via the air filters during a car wash.

Another cause of hydrolocking is a damaged head gasket. Head gasket seals the cylinder head to the engine block while also acting as a seal to prevent coolant and oil from leaking out. When it’s damaged, it can cause coolant to leak into the cylinders; remember, the only liquid that is supposed to be in the cylinder is fuel.

Another rare but possible cause of hydrolocking is damaged injectors or intake valves. A leaky injector or one stuck in the open position can allow excess fuel into the engine, causing engine flooding. While fuel is the right fluid, too much of it can also be an issue.

hydrolocked engine symptoms

What are the signs and symptoms of a hydrolocked engine?

The following are hydrolocked engine symptoms to look out for— abrupt engine stalling, engine sputtering, thumping and knocking noise, and engine not turning over.

Engine stalling

One very common telltale sign your engine is suffering from hydrolock is the car suddenly stalling. When too much water gets into the engine, the piston stops rotating since it’s unable to compress the water. As the piston stops, so does your car.

Engine sputtering

Engine sputtering occurs due to the inability of your engine to achieve complete combustion. Typically, when water fills the cylinder, complete combustion cannot be achieved due to the inability of the piston to compress the water. Incomplete combustion means the engine is not getting enough power. When the engine doesn’t get all the power it needs to start, it sputters.

Thumping and knocking noise

When too much water fills the cylinder, it doesn’t allow space for combustion to take place. This causes that knocking noise you hear when you turn off the engine. A hydrolocked engine sound like a crashing car.

Engine not starting again.

When an engine is in motion before being hydrocked, you can keep going at least for a while, that’s if it doesn’t stall. However, when you stop the car, it may refuse to start again since combustion cannot take place due to water inside the cylinder.

Engine not starting at all.

The above is for cases when the engine was already running when hydrolocked. However, in cases where hydrolocking occurs when the car is off, like during floods when cars get fully submerged, the engine won’t even start at all.

Also, hydro locking can also seize your engine and shut it off even if it occurs while driving. So, for those asking, will a hydrolocked engine turn over? Now you know it typically depends on when hydrolocking occurred and the quality of water that enters the engine.

What are the risks and damages of a hydrolocked engine?

Hydrolocking can cause many car problems, including broken rods, damaged crankshafts, corrosion, etc.


Water generally doesn’t agree with metal. So when water gets into the engine and stays for long, it causes the metal parts of the engine to rust faster than usual.

Broken connecting rod

The connecting rod, also called con rod, is an engine component that links the piston to the crankshaft. When too much water enters the cylinder, the pressure can cause the rod to bend or even break, especially if the engine can take a large amount of water. A broken con rod can also lead to complete engine damage since it bore holes into the engine block.

Damaged crankshaft

The crankshaft is responsible for converting heat to energy needed for your car to work. When the connecting rod breaks, it forces the crankshaft to move upward and stop suddenly. The force created by the abrupt stop may crack the engine block, exposing the shaft.

Worn out bearings

Bearings help in the reduction of friction and enhance the smooth rotation of parts. They can get corroded when in contact with water, making them wear out quickly.

Cracked cylinder head and cylinder wall

Water inside a fast-rotating engine causes pressure to build up inside the cylinder. This can cause the cylinder wall or head to crack over time.

Moreso, broken con rods create large metal pieces that bounce around the cylinder and into the crankcase due to pressure inside. The force exerted on these sharp metals can lead to holes being bored into the cylinder block and sump, causing leaks or cracks in the cylinder walls.

Seizing of engine parts

Hydrolocking does the most damage when the engine is running. Typically, the engines consist of moving parts. When water gets into it while running, these moving parts can stop suddenly. This sudden stop can typically damage these parts.

hydrolocked engine repair cost

How to prevent occurring engine hydrolock?

The most common way to prevent an engine hydrolock is avoiding the potential causes, at first. However, one may not have control over this all the time. A good example is during a flood when you’re unable to move your vehicle to higher grounds in time.

Who would even think of it at such times? However, while some are totally unavoidable, here are ways to prevent water locking.

Avoid driving through deep water.

Don’t drive through any puddle or other water sources without knowing the depth of the water and how high your air intake is. Hydrolocking will occur when the air intake gets submerged in water.

Suppose you see that the water level is high in the direction you are heading; consider taking another route. If there are no other routes, look for means to take your car across without going through the puddle.

Avoid cars with very low air intake.

Cold air intake helps in boosting car performance but can cause hydrocking.  Typically, cold air intake is the process of sucking air into the engine from outside the engine. Most air intakes are mounted too close to the ground, so it draws in air faster.

However, during heavy rain or flooding, the intake draws in water instead of air since it’s very close to the ground. Cold air intake hydroclock (hydrolocking caused by water entering the engine via the air intake) can be avoided if you avoid cars whose modifications place air intake in very low spots.

Don’t park your car under a heavy rain.

During heavy rain or storms, the road may likely get flooded and water may enter the engine. Even if flooding doesn’t occur, water may somehow find its way into the engine.

Don’t wet the air filter.

One way water gets into the engine is through the air filter. Air filters are placed close to the engine, so any liquid on the filter will likely enter the engine. So, when washing your car, avoid spraying water close to the air filter.

Regular maintenance is key.

Taking your car for routine maintenance will easily make you spot issues of hydrolocking in time. Suppose the vehicle is on the brink of hydrolocking; professionals will quickly decipher it and prevent it from happening.

For example, head gasket hydrolock (hydrolocking caused by a failing head gasket) can be voided if the broken head gasket is spotted and fixed in time.

Moreover, even if the engine is already hydrolocked, these experts can still repair it before severe damage occurs.

How to fix a hydrolocked engine?

An engine suffering from hydrolocking can be fixed. However, how much effort, time, or money you put into it will depend on the severity of the damage already done.

Typically, hydrolocked engine repair cost ranges from $700-$4000 depending on the extent of damage. You can totally avoid this high cost if your vehicle has comprehensive coverage—an insurance plan that covers repair costs for engines damaged by water, fire, vandalism, and theft.  However, there is something you must know about hydrolocked engine insurance claim.

Most insurance companies will only handle repair costs if the damage occurs due to unavoidable circumstance, such as flood. If, however, it happened due to carelessness, such as leaving your car under the rain or driving through deep puddles, you will have to foot the bills yourself.

That said, here is how to fix a hydrolocked engine, whether it’s a hydrolocked engine with oil, coolant, fuel, or water.

  • Start by draining the fluid from the engine cylinder by removing the inlet manifold. If this doesn’t fix the problem, continue to the next steps.
  • Dismantle and disassemble the engine.
  • Inspect the bearings, cylinders, pistons, and other engine internal components.
  • Replace damaged engine parts.
  • Carry out pressure testing on the cylinder to ensure they are still in good shape.
  • Check the cylinder head for cracks.
  • Reassemble the engine components and mount it.
  • Test run the car to see if it’s working effectively.

These steps above can work for just any engine. So, whether it’s a hydrolocked motorcycle engine, hydrolock BMW, or Ford, it works for all.

How to avoid common mistakes and myths about hydrolocked engine?

Here are common mistakes and myths about hydrolocked engines to steer away from. As these myths may even cause you to hydrolock the engine even when you could avoid it.

Check first before going through

I have stated that you shouldn’t drive through water unless you know how deep it is. But how do you know how deep it is? Watch other cars driving through, especially those of the same size as yours.

Another way to avoid it is to look at the water level against your car.

If it’s above your wheel level, there is a high chance that water will reach your air intake. Do not cross in that situation. You can also wait on the other side of the road till the water drains out. If you don’t have such patience, then go through an alternative route.

Stop when stuck

Suppose you make the mistake of entering into a puddle and get stuck; shut off the engine immediately and look for means to pull out your car. Allowing the engine run increases the chances of water entering the engine and getting water-locked.

Protect the air intake instead of the exhaust

Hydrolock occurs because water entered the cylinder through the air intake and not because water entered via the exhaust. People often feel that water will likely enter via the exhaust because the exhaust is at a much lower position than the air intake.

So, instead of the exhaust, be weary of the air intake. While direct outside water can’t enter the exhaust to the cylinders, it’s possible. See explanation in the next paragraph.

Water can enter the cylinders through the exhaust.

Suppose you drive through deep water; water may enter the engine electronics and shut down the engine. During this time the engine went off, the water might flow back through the exhaust to the cylinder since no exhaust gas is coming out from the exhaust pipe. Here, the highest repair will be to repair the control circuit. Don’t try starting it again; just get it towed.

Don’t crank a stalling engine.

Your car may stall because, despite being careful, water still found its way into your cylinder or may have touched the engine’s electronics. However, such water will not hurt a stalled engine; the engine should be restored once the water is drained. For stalling caused by water touching engine electronics, don’t attempt cranking the engine; you may need to get it towed and repair the control circuit.

If, however, you choose to crank the engine, you will only worsen the situation. You’re trying to compress an incompressible liquid—running an engine with all its power against an immovable object. This is what leads to the bending of connecting rods, damaged pistons, and even cylinder and cylinder head damage. However, if your engine stalls and you shut it off, the highest will be getting your feet wet and your car towed.

Move only when the path is clear.

If you attempt driving past a puddle or large water, ensure no vehicle is in your path—whether beside, behind, or in front. You need to be on steady high revs, and you can’t do that while a vehicle stalls in front of you. Moreover, cars driving beside you may create water waves that can splash on your car and get your air intake.

Speeding doesn’t help.

Avoid driving too fast in water. Hydro lock can occur even before your engine stalls since your engine may have damaged the connecting rods even before your engine shuts off safely.

Shift to a lower gear.

For vehicles with paddle or manual shifters or those shifters with low/hill settings, shift your transmission to 1. The goal is to keep the engine on high revs as possible while maintaining low speeds (but don’t crawl).

Insurance helps

Repairing a hydrolocked engine is usually very expensive. So to avoid this, opt for hydrostatic lock cover, An insurance plan that covers the repair of engines damaged by water.

Final Words

So, a hydrolocked engine is one that locks up due to excess ingress of water inside the combustion chamber. This causes several car problems and, in the worst case, makes your car completely immobile.

While a severely hydrolocked can be repaired, doing this will cost you a lot of time and money. This is why it is important to prevent it from happening in the first place, as some causes are totally avoidable.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

2 thoughts on “What is a Hydrolocked engine? – Causes, Fixes & Preventions

  1. Hey Stephen,

    Try to turn the engine with a wrench and see if it will turn round. If it doesn’t, you likely have a hydrolocked engine.

    If that is the case, loosen the spark plugs and pour in a cover of transmission fluid on each plug hole and leave it overnight.

    The next morning, try to turn the engine by hand. If it works, put back the plugs and leave only one empty. When the engine starts, let it run for a few seconds to blow out the oil on the empty plug hole.

    After that, turn off the engine and tight the plug. Remove another plug and start the engine to blow out the oil on the next hole.

    Repeat the process until you are done with all the cylinders.

  2. Good morning,
    I have a 1.5 diesel captur with some of the above problems ie engine turns slightly then nothing, all levels look fine, car been sat in drive for a few months have checked codes , most relevant I can find relates to multi plug in engine bay , where should I start looking ?

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