How to Restart Car After Stalling in Water: Essential Tips

Driving into flood waters can be extremely dangerous. If your vehicle stalls in flooded cars, it is crucial that occupants safely evacuate as soon as possible. There are also important steps to follow after escaping flood waters and before attempting to restart a potentially hydro-locked engine, especially if deep floodwaters … Read more

Photo of author

Written by: Mohammad Sameer

Updated on:

Driving into flood waters can be extremely dangerous. If your vehicle stalls in flooded cars, it is crucial that occupants safely evacuate as soon as possible. There are also important steps to follow after escaping flood waters and before attempting to restart a potentially hydro-locked engine, especially if deep floodwaters have infiltrated the flooded car’s internal components.

Fortunately, by understanding the causes of flood stalls, assessing risks, utilizing weather forecasts, and following the proper engine restart procedures, drivers can often get their vehicles up and running again after minor flood stalls.

Key Takeaway

  • It is best not to immediately start the vehicle: Wait for a qualified mechanic to inspect the car to ensure there is no water in the engine or intake system.
  • Check the intake and engine for any water. If water is present, remove the spark plugs and crank the engine to push out the water. Replace the spark plugs and try starting the car.
  • Dry the electrical systems by moving the car to dry ground away from the water. If needed, use an air compressor to blow out any remaining water from the electrical components.
  • After starting the car, run it for a few minutes and check the oil level for signs of water contamination. Change fluids like oil and transmission fluid if necessary to prevent further damage.

Key Reasons Vehicles Stall Out in Flood Waters

The most common cause of vehicles stalling in floodwaters or large puddles is the engine taking water instead of air, which is known as hydro-locking or a hydro-locked engine. However, there are a few key reasons this dangerous situation occurs, life-threatening, and avoiding risky situations.

Air Intake Flooding

The main way floodwaters sneak into vehicles is through the engine air intake. This vent, often located low on the vehicle body, brings in air that mixes with fuel for diesel engine combustion.

When driving through floodwaters, the intake sucks in water instead of air which immediately hinders engine operation. Without proper airflow circulation, engine cylinders, compression, and ignition cannot properly happen.

Exhaust System Backups

Another way standing water or floods can lead to stallouts is hydro locking, backing up through the exhaust system. Specifically, as flood levels rise high enough, water enters the air intake and flows in the reverse direction up to the engine cylinders.

Having liquid water and air inside cylinders instead of typical exhaust gas buildup creates immense back pressure on the engine. Between this and ingestion through intakes, combustion stops and the car engine seizes up.

Short-Circuiting of Electronics

The final cause of flooded car engine stallouts is water exposure circuiting vital electronics throughout the vehicle. Key electronics like:

  • Ignition control modules
  • Fuel pump controllers
  • Various engine sensors
  • ECU and computer components
  • Alternators

The car’s air intake is very prone to short-circuiting when exposed to water. This can happen both through interior cabin flooding or under hood components taking on moisture. A short in the car’s air intake or any of these systems can lead to stall out.

In as little as 6 inches of moving flood water or 12 inches of standing water, vehicles, including cars, are likely to sustain water damage or engine hydro-locking stalls.

Hydrolock Causing Catastrophic Damage

If floodwaters rise­ high enough to start flowing into a car through multiple intake points and backup syste­ms, a dangerous situation can occur where one­ or more cylinders in the car fill with wate­r instead of just air and fuel.

With liquid trapped inside­ the car’s engine cylinde­rs and the key turned to start the­ engine, extre­mely high pressures can build up. This “hydro lock” or “hydrostatic lock” wre­aks havoc on internal components.

Water pre­ssure can snap or bend connecting rods. Pistons and rods ne­ar the tops of cylinders may shatter. Significant stre­ss is placed on crankshafts. Cylinder heads or e­ngine blocks could crack apart.

This level of me­chanical damage necessitate­s a complete teardown of the­ engine or eve­n a full replacement. We­ will discuss more details soon about the catastrophic e­ffects of a car becoming flooded and what ste­ps to take to drive safely in flood conditions.

Why Attempting Restart is So Risky

Once your car or truck has stalled in rising flood waters, top priorities should be safely evacuating occupants and getting to higher, dry land. At this point, immediately attempting to restart the car is very risky for the following reasons.

Flood Levels Can Still Increase

Depending on weather conditions upstream, floods can intensify after your initial car stall. Restarting the car will be futile if waters overtake the vehicle and occupants with even higher flooding. Monitoring emergency alerts, weather radio, forecasts, and NOAA flood notifications is strongly recommended.

Further Hydrolocking And Engine Damage

Trying to repeatedly crank a car engine that has deeply ingested water through hydrolocking will rapidly compound mechanical damage. With water trapped inside car cylinders, working components will bend, snap or break when attempting compression against the incompressible liquid.

Difficulty Tracking Vehicle Location

Fast rising waters may lift and carry off entire vehicles, limiting visibility and control for occupants in the process. This makes accurately locating the stalled car for evacuation or restart very difficult after floods subside somewhat. Additionally, cars can be swept for miles away from flooded roadways during floods.

Safety Hazard And Rescue Difficulties

Attempting to deal with restarting flooded car vehicles also puts driver and passengers at great risk if water levels are still high or rising after initial stall out. There is risk of slips, falls, injury, exhaustion or even drowning in life-threatening and risky situations if evacuating without emergency services present and monitoring for rescues. For these reasons, guidance in flood scenarios is to evacuate immediately to higher ground and let authorized responders assess car restart viability later.

For all these reasons, the recommended guidance is to evacuate stalled cars in water over 12 inches high and move to higher ground safely. Then emergency services can track safe driving in floods and attempt car recoveries as flood levels lower.

Safely Determining Water Depth Dangers

Safely Determining Water Depth Dangers

Before ever attempting to drive through standing water on roadways during floods, drivers must understand depths likely to start risking engine hydro locking stalls.

As a general emergency preparedness rule for vehicles:

  • Sedans and small cars will stall out in as little as 12 inches of standing water or less if moving
  • Small crossover SUVs face stall risks starting at 14-16 inches typically
  • Large trucks and SUVs can start seeing issues by 18-24 inches in depth during floods

Emergency Safety Tip:

Roll down windows before water gets too high surrounding vehicles to allow emergency escape! Even if vehicles have power features, once electronics are fully submerged doors and windows will be impossible to open. Planning is key.

The reality is even modern vehicles should never attempt moving through flood waters if the depth is unknown or appears to be approaching bumper cover height. It only takes ingesting small amounts of water through intakes or exhausts to stall out. Turn around instead and take safer alternate routes where possible, avoiding risky situations in flood zone weather.

How to Restart Car After Stalling in Water?: Step-By-Step

If your vehicle encounters relatively shallow water before completely stalling out, you may have luck successfully restarting once moved to dry ground. The key is completing the process to prevent hydrolocking before catastrophic damages occur internally.

Note: Have the vehicle towed to a professional mechanic afterwards for a full inspection of all engine and electronics components after any level of driving through standing water.

Follow these step-by-step restart actions:

1. Shift into neutral gear to disengage engine power and reduce load on starter.

First, shift your automatic transmission into neutral gear or press the clutch on manual vehicles. This “frees up” drive systems and reduces the load on starter motors when attempting to restart.

Neutral gear also disengages engine power from possibly damaged wheels, axles or driveshafts from forcing movement if restart succeeds. This prevents causing further mechanical damage or loss of vehicle control if temporary driving to safety is possible after a flood stall.

2. Try 5-10 second ignition bursts to pump out water before straining systems.

With gears disengaged, next try 5-10 second ignition bursts without cranking starter motors continuously. This may initially pump some water out of flooded cylinders before straining systems.

Intermittently attempting ignition this way is lower risk compared to holding keys in the start position with already hydro-locked cylinders. Limiting cranking durations also prevents burning up damaged starter motors and provides engine protection.

3. Allow 30-60+ minutes of drainage time for water to drain from cylinders, intakes, and exhausts.

If vehicles stall out during floods but components are not yet catastrophically damaged, allowing gravity drainage time of 30-60+ minutes can be extremely beneficial. This allows any collected water in intakes, cylinders or exhausts to potentially drain off before restarting strain.

Be patient and allow assumed hydro-locked vehicles these drainage periods before reattempting start procedures. However, if rising water levels start threatening safety again, evacuate immediately. Vehicles can wait – safety first.

4. Jump start battery to assist flooded electrical components to turn engine over.

After allowing ample time for potential cylinder or intake drainage, engine restart efforts will likely need battery jump-start capabilities. Either set up jumper cables to a running donor car or utilize a compact jump starter box appropriately sized for the vehicle.

Flood-damaged electrical components often struggle to turn engines over without an auxiliary power boost. Be prepared with proper jump-start equipment in emergency roadside flood kits.

5. Carefully drive out of flood water to safe ground immediately if restarted.

If vehicles successfully turn over and start after the previous steps, the immediate goal should be carefully but steadily driving out of flood waters and to safe, dry ground. Avoid revving engines highly or idling in place.

This prevents potential re-ingestion of lingering water that could reintroduce hydro-lock conditions or further damage components from immediate stallouts. Priority one is safely escaping flooded zones compromising vehicles.

6. Professional Inspections vital After Any Stalls

Even after successfully restarting engines and escaping flooded waters, immediate repairs are likely still needed before regular road use. At a minimum, all air filters, fluids, spark plugs and electronic ignition components will require inspection and potential replacement after water exposure.

But much more severely, deeper water stall events likely caused internal engine damages from hydrolock conditions. Connecting rods, cylinder walls pistons, bearings and crankshaft journals should all be checked for proper tolerances and operation. For this reason, towing flooded vehicles to professional auto repair shops is highly recommended over personally attempting repairs after hydro lock stall incidents.

While the above covered proper restart procedures, internal combustion engines involve countless precisely engineered components critical for operation. After catastrophic failures like hydrolock bending rods or cracking blocks, most average car owners do not have the expertise to execute full engine overhauls or rebuilds. Trust qualified mechanics to assess damages and handle any needed disaster vehicle repairs.

Comprehensive Details on Vehicle Hydrolocked Engines

Comprehensive Details on Vehicle Hydrolocked Engines
Image Source: Kristopherspencer.Wordpress.Com

Now that we’ve covered the proper restarting procedures, let’s discuss in more depth exactly what happens inside engines flooded catastrophically by deep water ingestion. This ultimately destructive mechanical process is referred to as complete hydro locking or creating a “hydro-locked engine”.

What Exactly is a Hydrolocked Engine?

The term “hydro lock” or “hydrostatic lock” refers to when an engine’s cylinder fills with a non-compressible liquid rather than the proper air/fuel intake charge. This locks up, seizes, blocks or traps pistons from moving through full compression strokes.

In worst-case hydrolock scenarios, one or more cylinders fill with water or flood debris mixtures rather than just air and atomized fuel. But with liquids being impossible to compress under combustion chamber heat and pressures, pistons cannot properly move as crankshafts attempt to rotate during ignition.

The engine essentially turns into a hydraulic press pushing against incompressible water rather than compressing gases! Let’s look closer at the mechanical devastation this causes inside severely hydro-locked car and truck engines:

Bent Connecting Rods

One of the most common forms of damage in hydrolocked engines is bent or broken connecting rods. These “rod” components connect pistons to rotating crankshafts, transferring combustion pressures into rotational energy.

But when cylinders fill with water and attempt compression, immense hydraulic pressures snap weaker connecting rods or bend them out of reusable shape. This also usually damages attached piston heads in the process.

Piston Destruction

Speaking of pistons, they usually suffer severe damage in hydrolock conditions for a couple of reasons. First, most automotive pistons include cutaway reliefs near the top to allow room for valve openings.

With incompressible liquids trapped in cylinders and nowhere to escape, immense pressures focus directly on these relief notches. This often results in cracked or broken piston tops when hydrolock compression pressures occur.

Any pistons that avoid cracking usually end up scratched or gouged along cylinder walls, making them useless for further service. Replacement sets of forged pistons, or entire engine blocks, are required after hydro-locked engine damage.

Cylinder Wall & Head Damage

Pressures deforming or breaking pistons inside deeply flooded engines also cause collateral damage throughout surrounding cylinder structures and surfaces. It is very common to find cylinder walls scrapped or gouged, rendering them unusable tolerance-wise for sealing combustion gases efficiently.

Likewise, most hydrolocked engines usually bend or crack cylinder heads that contain valves controlling intake and exhaust flow. With water trapped inside instead of flowing gases, extreme transient pressures pit and warp head sealing surfaces. This requires extensive machining efforts or outright head replacements.

Cracked Engine Blocks

In the worst-case hydro-lock scenarios with extreme water or debris ingestion, compressive stresses can crack solid engine block castings. With components like pistons, rods and crankshafts mashing together incompressibly, something has to give – often the thick engine casing itself.

While not extremely common, cracked engine blocks essentially total older vehicles. With extensive disassembly and machining required, fixing engine damage and changing components, expensive repairs outweigh most ageing car values. This makes parting out or selling such flood-damaged vehicles for scrap metal or rebuilders the only sensible option over attempting to personally replace entire engine castings.

Bent Crankshafts

Finally, bent crankshafts are also a possibility from hydro-locked stall events, although not extremely common in modern engines. If multiple connecting rods snap or piston crowns break off under pressure exerted by a water-filled cylinder, fast-spinning crankshafts can also twist or skew within pressed-on bearing journals.

Repairing bent cranks requires speciality machining that most average shops cannot perform. But like cracked engine blocks, with enough collateral damage to rods, pistons and cylinder surfaces, further crank repairs become moot. At this level of mechanical destruction, engine swaps or sales to scrap yards make the most financial sense.

Signs an Engine is Likely Hydrolocked

So between severe connecting rods, pistons, and cylinder and crank damages, deeply hydro-locked engines often require extensive mechanical repairs costing thousands. But how do drivers know if attempting to restart flooded vehicles is even safe after initial stall-outs?

Watch for these warning signs of likely water ingestion before cranking ignition again:

  • Milky/foamy engine oil
  • Water or chemicals dripping from the exhaust
  • Previously functional electronics no longer working
  • Immense difficulty slowly cranking over

Finding puddled water, oil or debris around tailpipes, undercarriage or wheel wells also indicates likely hydrolock intake issues.

Likewise, noticing air filters soaked through with water is a clear sign of heavy airflow ingestion into the engine. In such flooded cases, further, restart attempts risk rod puncturing engine casings requiring rebuilds! Seek repairs.

FAQs on Hydrolocked Car Engines

What Is A Hydrolocked Engine?

A hydro-locked or hydrostatic lock engine refers to internal cylinders being filled with liquids such as floodwater or oil, which stops pistons from properly compressing on ignition.

What Happens To A Hydrolocked Engine?

The incompressible liquids inside cylinders bend or snap connecting rods, damage pistons, warp cylinder walls, and break crankshafts when the engine tries to turn over. This requires full engine rebuilds.

Is My Engine Hydrolocked?

Signs of a hydrolocked engine include water/liquids in cylinders, inability to turn over, and flood damage to electronics. Milky oil and debris or chemicals in vents indicate water ingestion that requires repairs, and fixing engine damage before restarting.


The above restart procedures, details on hydro locking and compressed lists cover critical information drivers should know in the event of breakdowns in flood waters. While the exact required repairs or replacements will depend on damage levels, the priority focus is always on occupant safety in dangerous weather conditions. Monitoring emergency alerts, acting quickly, and avoiding vehicles during flood risks are the best ways to prevent hydrolock stalls.

Leave a comment

About Mohammad Sameer

My name is Mohammad Sameer and I have over 3 years of hands-on experience repairing cars, motorcycles, and trucks. Ever since I operated on my first engine in 2018, I’ve been passionate about all things automotive. In 2021, I launched my blog “Motoring Mastery” to share my knowledge with car enthusiasts and DIY mechanics.