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How Deep Is That Puddle?

How To Deal With Flooded Roads....

driving on a flooded road.

       Flooding can happen any time thanks to the rain, blocked drains or burst water mains. Surface water depth from these can be hard to predict and be very deep.

Manhole covers can get lifted and moved or a sinkhole opened up in the street that you can’t see.

      It’s best to avoid driving through water, especially if you’re not sure how deep it will be. The safest thing to do is go around puddles when you can and "NEVER EVER" drive through moving water over 4” inches.

Most experts say not to drive through more than four inches of moving water!

Fast-moving water is very powerful – take care or your car could be swept away.

Note: 1’ foot of moving water can easily push a car off the road.

      Just driving through a few inches of water, better take caution. It’s not that deep, but if you drive through to fast, you risk splashing water into your intake or getting electrical components or wiring wet. Water plays havoc with electronics and wire connectors.

      In addition to engine electronics, you could have problems with the Anti-lock brakes sensors, failed suspension and steering components or wheel bearings. Problems may not surface until months or years later.

Puddle depth

      On many cars, the engine’s air intake is low down at the front. It only takes about a ¼ cup of water to be sucked into your engine to wreck it, and if the engine sucks in water (known as “hydro lock) …you may be saying good-bye to the engine.


make sure your tail-pipe/exhaust doesn’t get submerged. If you drive with your tail-pipe/exhaust underwater and back off acceleration enough, you will suck up water into your exhaust system.


driving too fast into a shallow puddle can lead to hydroplaning especially if your tire tread is worn down to low. The front tires are lifted and no-longer make contact with the road.  You will lose steering control.

submerged exhaust pipe

        To help avoid hydroplaning, slow down. Go over puddles in a straight line. Steer lightly (avoid doing too much steering adjustment) and very light braking if any until the puddle is crossed. If you need to use the brake a lot to slow down, you entered the water with too much speed.

“You should never drive through water above the vehicle’s rocker panels if at all possible”.

Flooded road ahead.

      If you encounter flooded roads on your journey, it's important to approach them safely. Just remember, if you can find a solution that doesn't involve driving through floodwater, you minimize the risk to both you and your car.

      It's almost always worth turning around and finding a different route as a better option than stalling trying to drive through it.  You'll regret ruining your car just to save a few minutes of time.

      Modern vehicles’ door seals are generally water-tight (unless old and cracked or worn) and keep water out, but this can make a car buoyant, so they can start to float when driven through water that's only 11” inches deep leaving you stranded.

     Based on your vehicle’s height, you can better determine the odds you can safely go through a large body of standing water on a road.

     If you decide to go through, predetermined your route. Enter the water slowly (about 1-2mph), before accelerating to about 3-4mph to create a bow wave and keep water out of the engine.

Just make sure you always control your speed.

If you are driving an automatic: you will need to use the brake at times to control your speed since even at idle speed, you could easily go too fast.

If you are driving a manual transmission: keep your vehicle in a low gear (2nd gear is generally adequate) and engine RPMS up at times.

     Drive as if you are in a boat in a “no wake” zone, but much slower. If you see any white caps in the wake you leave behind, you are going too fast. The wake you leave with your car should be extremely slow and gentle.

     While driving through water like this, it can get frustrating driving trying to drive as slow as you can but steady to prevent damage.  In this case, you don’t want to go too fast or stall.

Drive slowly through a flooded road to avoid stalling.

Remember. Avoid creating large waves. Large waves of water can "hydro lock" the car if the water is sucked into the engine.

      Drive at the highest part of the road when possible and do your best to maintain a slow steady speed to avoid water entering the exhaust pipe. Also avoid the temptation to make a quick exit.

    Once you exit out the water, be careful not to accelerate to fast as the road surface past the water’s edge could be slippery from other vehicles dripping water as they exited.

Note: if there were leaves in the water, check the radiator for blockages at the earliest you can.

     Also, don’t turn the car off right away. Let it run a few minutes to dry it and blow and dry out the muffler. That’s if after you exited the water and won’t be driving for too long after.

     The big thing to take care of is your brakes. Ride them a bit after you come out of the water to create some friction so the generated heat will evaporate off any excess moisture.

Essentially you are drying them by this method and keeping braking performance as effective as possible.

What to do in Heavy Rain, Flooded Roads and Standing Water.

Heavy Rain.

  • Turn your headlights on – the law is: Wipers on. Lights on! Always turn your headlights on when visibility is reduced exception – Sun glare.

  • Use fog lights if the vehicle is equipped, but switch them off when visibility improves.

  • Leave twice as much space between you and the car in front – it takes longer to stop on wet roads and you have more time to react.

  • If your steering feels light due to hydroplaning, ease off the accelerator and slow down gradually.

  • If you break down don't pop up your car hood while you wait. Rain-soaked electronics can make it harder to start the engine.

Floods and Standing Water.

  • Try to avoid standing water if you can or drive slowly through it.

  • Don't drive into flood water that’s moving or appears to be more than 4” inches deep. Don’t hesitate on letting approaching cars pass first so you have a way of gauging its depth.

  • Drive slowly and steadily so you don’t cause too much splashing or make a bow wave.

  • Test your brakes as soon as you can after exiting the water.

  • If you do get stuck in flood water, it's usually best to wait in the car and call for help rather than try to get out.

  • If you stall or have to sit for a long time in over 1’ foot of water, then checking of the fluids for water is essential. When the water dries up, change all your fluids (brake, trans, oil, radiator, differential, steering, etc). Then change them all again in a week or two to make sure any water that got in is gone.

How Water Effects Your Vehicle.

1) Engine Intake System: Water in the intake system ultimately gets into the cylinders, in which pistons compress air.

But water doesn’t compress, and the resulting pressure inside the engine can bend piston rods or crack the engine block. Either essentially ruins the engine.

2) Transmission: Water makes the gears slip.

3) Brakes: If the rotors are extremely hot, exposure to water can warp them. The result is your car will vibrate when you try to brake. Water may get into the brake lines and cause brake failure immediately or later when you least expect it.

Brake specialists suggest that, after rolling through deep water, drivers pump their brakes to squeeze water from the pads.

Car damage from driving through a deep puddle of water.

Image from:

4) Electronic Systems: Many manufacturers install automobile computers in the floorboards and under the seats. Water damage to these components can result in all sorts of electrical and electronic problems.

What Happens When An Engine Hydro Locks?

Hydro locking is when an engine either seizes or suffers catastrophic failure due to the ingress of a substantial volume of liquid in the cylinders. 

Air is compressible so causes no problems, but liquids are generally not. This means the piston cannot move in the cylinder because the liquid cannot expand/compress to allow that.

With an internal combustion engine effectively resembling a form of an air pump, the internals are all designed to deal with the compression of air. Not liquids.

Final Note

Between possibly falling into an unseen sinkhole, engine sucking in water and hydro locking, the after-the-fact corrosion that can take place in body cavities, wiring connections, etc., and the mold and mildew that can result from saturated fabrics, there are way too many ways that driving through deep water can destroy your car…and/or render it valueless.


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