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I have read many warnings about driving a car through deep water. Some problems that this can cause is destroy the catalytic converter and in petrol engines water can cause damage to spark plugs. And in diesel cars I thought you needed a special exhaust if you want to drive with the engine underwater. And I also saw a video about a car that had its engine destroyed.

How much of this is true? And how do those 4 wheel drive cars drive with their engines submerged in muddy water ?

I have myself driven a Toyota yaris through water as high as the top of its wheels and nothing happened although I did keep the engine on high revolutions.

What is the recommended thing to do if you need to pass through an area that's been flooded? (Ofcourse the answer will depend on the car)

I have seen many videos and pictures of cars driving through deep water and here are two examples: 1. https://m.youtube.com/watch?v=ednZi2T-TsA&t=58s 2. https://m.youtube.com/watch?v=LC5ld79joIA

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    Anecdotally: my father and I have driven his 95 Land Rover Defender 90 through a river that went up to the hood level before. He taught me that it’s safe in an off road vehicle like that provided you never slow down because moving causes a wake to form in front of you so water does not literally flood the engine. If you get stuck because of a log or something in the river that you can’t see then the wake goes away and the water comes in .... – Max von Hippel Feb 15 at 22:33
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    @MaxvonHippel Did that Landy have a snorkel fitted? Some do, some don't, and it makes a big difference, though comparing any Defender with 'normal' cars is unfair. – Mike Brockington Feb 17 at 15:37
  • No snorkel. But we were with a large group of other land rovers at the time so we didn’t worry too much about getting stuck as in a worst case scenario one of them could have winched us out. – Max von Hippel Feb 17 at 15:42
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The term you're looking for is Wading Depth which is specified by the manufacturer. They may surprise you, and its info you should know about your vehicle. Its in your manual, or search it online.

Examples

  • Jeeps say 500mm, and some models go to 700mm
  • Mercedes GLC SUV has a wading depth of just 300mm
  • Landrover Discovery (not the more compact Discovery Sport) has a wading depth of 900mm - this is the depth where the rear starts to float.
  • A Nissan Leaf has a colossal 700mm maximum wading depth - yes an electric car.
  • A Nissan Fairlady has an air intake behind the headlights, so its only able to go around 2 inches of water, and that assumes flat still water.

The safest assumption for any car is DON'T drive through water. Next is "no deeper than the sills on the car. For a car-based SUV its no more than a car. For a proper 4WD then "center of the wheel's axle" is a safe minimum. All this assumes an unmodified vehicle.


Discussing the two videos:

The first shows a pair of relatively unmodified utes (pickup trucks) attempting to drive upstream against water flow. They are not in the center of the river, so are likely on a slightly shallower ledge.

The vehicle nearest camera is stuck because its traction is equal to the pressure of the oncoming water, which is why it can't make headway. The passengers are bouncing to try and increase the traction.

The Isuzu DMAX ute has a fresh air intake right over the wheel arch nearest the camera. Its more at risk from flooding the alternator, which is slightly lower.
enter image description here

These two vehicles are at about their maximum depth for water crossing.

RISKS: Thankfully they're playing in the shallows - the end of the recording shows a small protrusion upstream, shielding them from the worst of the river's flow. Had they tried to cross the river at this ford, it would have ended up with vehicles floating downstream out of control. Notice the nearer vehicle gets out by moving right, into a shallower area and then gets traction. The further vehicle ends up being pushed backward by the river flow. And there's a lot of water released out the driver's door at the end.


The second shows a modified Australian Toyota series 80 crossing a ford that is really a too deep for a safe crossing. The vehicle floats because the ground has dropped too far below the water surface. This causes a loss of traction, and the slow current pushes the vehicle downstream. This is a bad situation and now the driver has no control. Fortunately the river bed got slightly shallower near the edge, the speed of the water current slowed, and the front wheels got enough traction to overcome the current. Now driver has regained some control and can edge into the shallower area, and get out.

RISKS: vehicle risked being washed downstream out of control, and possibly snagging and turning over. This was incredibly dangerous, even though it was relatively calm. Ideally they would have roped up to the rear towhook so that it could have been pulled back out once floating, but once traction is lost then its gone from planning to reacting

Another possibility would have been to allow the vehicle to fill with water, decreasing its floatation, and letting it get traction. Risk here is that you're sinking and may drown yourself. Plus all the stuff inside is going to get wet (which happens anyway, notice the driver's door at the end)

Still from second video

In the still-image above, notice the large black plastic air intake on the A pillar, sweeping down into the driver's side wing? This is an air snorkel, and the engine breathes in here. Its the motor equivalent of

enter image description here

When the snorkel/schnorkel's end goes underwater, the engine will draw water in with the air, and will suffocate and stop, potentially causing expensive internal damage. You don't want that.

It doesn't have to be water either - enough spray or rain or mist can cause issues for the engine too.

There is no need for an exhaust snorkel - the gasses will force the water out the tailpipe and bubble up, as long as the engine is still running. Some dual tailpipe exhausts have issues if there's a common chamber, where one side floods and the other side keeps venting.

If the engine stops in water, you're pretty screwed. Best practice if the water is over the axle/wheel hub is to be towed out and then restart motor. But you may be blocking the path out. Time is also critical, the longer you sit in water the deeper your wheels will sink in, and the more water ends up in the cabin. Plus allows more time for water to get into your electrics.


Here's another snorkel, showing how it connects to the air filter/airbox. I have personally driven this through water that was over the bonnet (hood). Fortunately it was compacted shingle so a good firm footing. Had it been mud or silt or loose shingle, then that would be much riskier.

Own work, own car

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    Yes - that's a flower pot and a Marley plumbing elbow on the landrover. Your eyes do not deceive. – Criggie Feb 14 at 23:36
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    Axle breathers? – Pete Kirkham Feb 15 at 1:02
  • @PeteKirkham Excellent point - the manufacturer's wading depth rating will cover the entire vehicle's stock design. If the depth is limited by the axle breathers, then so be it. The landrover above has its front diff vented into the snorkel, and its rear diff into the galv valence trim, so it could go to 1.7 metres at the front and about 1.0 at the rear. No way would I do that though. – Criggie Feb 15 at 1:30
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    In the movie Dante's Peak, Pierce Brosnan drives a Chevy Suburban with a snorkel through a river. He loses traction when floating but regains it when the cabin fills with water - weighing it down. It's just a movie but not unrealistic. youtube.com/watch?v=ZyLi2ApFhbY – Hannover Fist Feb 16 at 22:38
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    Recent stock JEEP Rubicons specify 30" (762mm). I've tested them at roughly that height. The battery and intake are fine and they seem to have sufficient traction as long as you keep moving. Door seals in my experience hold well. Drain plugs don't once removed (use rubber cement to lock them back in place.) I would not recommend going that deep if the water is muddy. You may overheat. You also may miss an even larger drop off. – mreff555 May 20 at 18:48
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One of your questions as stated and not answered is:

What is the recommended thing to do if you need to pass through an area that's been flooded?

The answer to this has nothing to do with Mechanics.SE, but I'll answer it anyway ...

Bottom line: DON'T DO IT.

It has nothing to do with whether your car can run through the water and survive. It has EVERYTHING to do with if you can survive. The big problem here is, you cannot see what is under the water. You cannot see if the road has been washed out. You cannot tell if it is safe to drive through, regardless of whether or not your car can even make it through it. In some areas when the area is flooded, the water may look calm, however there may be currents which can sweep your vehicle off of the roadway. When this happens, you have absolutely no control. You run the SEVERE risk of drowning in a situation such as this. This is the MAIN reason you should not drive your vehicle in a flooded area.

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    Don't drown, turn around! – Moab Feb 14 at 15:21
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    Another reason not to do it -- mold/mildew. Unexpectedly ran into water just above the sills, got through, didn't see any water get inside the car, water was fresh rainwater (relatively clean), but I never completely got the smell out. (very flat area, no risk of drowning, but still would have avoided it if I was paying attention) – Mattman944 Feb 15 at 9:22
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    This is completely valid advice and a good idea while not addressing the "how" part of the question. There are a surprisingly small number of reasons why someone would HAVE to drive through water NOW. Waiting for the water level to drop, or finding another route are generally safer. Reasons like "I have to get to work now" are debatable - its not worth the risk, whereas "I'm stuck on this island and its going underwater now" is a different matter. Answer must stay cos its excellent advise in this situation. – Criggie Feb 15 at 22:35
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    Also, floodwaters have been known to dislodge manhole covers, which would be quite unpleasant to encounter with a wheel. – shoover Feb 16 at 2:27
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    @all My impression is that most of this back and forth on question answering strategies is more suitable for a chat room or a meta question. As there is already a chat room for discussing this question and the associated answer, I've marked most of the off-topic comments as no longer needed. Feel free to discuss in that room. Please be mindful, though, that this site needs to always remember that actions or techniques discussed here can have life-altering or life-ending consequences. – Bob Cross Mar 8 at 15:51
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Generally the car shouldn't be driven through water! On your Yaris, where you had high revs, what would happen if your air intake was submerged would be that your engine would fill some cylinder(s) with water and since water doesn't compress it would bend a piston. This is called hydro locking and is often a catastrophic failure. So don't do that if you want to keep driving your car.

Now if you would like to make your car go in deep water there are certain things you'd have to "fix". First of all, where will the engine get its air from? Some cars have their air intake low down in their engine compartment, others have it high up, the higher and farther back the better (for this). In the second clip you can actually see that they have fitted a snorkel (passenger A-pillar), so air supply is secured for very deep driving.

There are also certain techniques for driving in water. Not too fast, but fast enough to create a bow wave:

bow wave

Then we get to electronics. Most electronics on a car are somewhat water protected. However this depends on brand and age etc. A very good tip is not to get your ECUs submerged! Often computers are located inside the car, will the car interior stay dry (some cars are built to be dry, but most are not).

Exhausts for diesel I don't know anything about, but a petrol car will work. However I can't imagine that it's very good with the rapid heat changes.

One last consideration: salt water... just try to stay out of salt water altogether. Salt water is corrosive on almost all parts of your car. Electric connectors will can over time go bad (might be very hard to find). Stuff will start rusting. If your in salt, make sure to clean it very thoroughly!

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    Ether with a snorkel, slowly, or unsuccessfully. – Mazura Feb 15 at 0:09
  • Now THIS answer by Markus is addressing the question, as opposed to this diversion answer regarding safety. – tgm1024--Monica was mistreated Feb 15 at 20:51
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    If you have driven through salt water, a quick fix is a splashy trip through fresh water, like a riverbed, to wash off the salt water. If your country salts roads in winter then idling back and forth over a running garden sprinkler can do most of the work. For a great cleanup, a steam clean in the engine bay and around the chassis is a good idea. Once clean, park the vehicle in the garage to dry off, don't leave it out in the cold. – Criggie Feb 15 at 22:43
  • BONUS: Found this clip some years back. To be fair they go very deep, and also get stuck, so the water gets more time to leak in. Anyways, in the video they drain all the oils in the car. It's not good! But funny to watch, enjoy: youtube.com/watch?v=vpY6mdP2aRE – Markus Feb 17 at 7:52
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There are a lot of variables here, but key risks are:

  • water shorting electrical systems
  • water being sucked into air intake (or potentially into exhaust)
  • cold water coming into contact with hot metal causing thermal shock

The first one is very dependent on where and how wiring systems are routed and protected. Fuse boxes, connectors, battery etc are typically mounted reasonably high, but going into water fast can easily cause splashes to hit sensitive areas. And deeper water means it won't just be splashes.

Air intakes can be moved for safety - see snorkels on many off road trucks to allow air to be taken from well above the water surface - but some are very low, eg in the wheel arch, or behind the front bumper. It's very easy to flood the engine with uncompressible water and destroy it.

Exhausts can also be an issue - running at higher revs in low gears gives less chance of water flowing in the exhaust, but try and avoid changing gear, as that could give an opportunity for flooding.

Thermal shock is one of those unpredictable ones - you can shatter blocks or turbos, but you may be fine - it's a risk.

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  • Don't forget water in the intake can bend connecting rods! – Moab Feb 14 at 15:20
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    Another point - water entering the cabin makes the passengers somewhat vocal. More-so when its cold water. Then exponentially louder as depth increases and they realise their phones and lunch are at risk. – Criggie Feb 14 at 23:59
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Later, they will sell the car to a sucker

And that poor sucker will have constant electrical problems, which cost them thousands in attempted repairs, and ultimately lead to scrapping of the car.

If you don't believe that, I've got a perfectly nice flood car to sell you!

Modern cars are highly electrical. They are more of a computer with an engine bolted onto it, than the other way 'round. If you don't believe me, pop your hood and look. This involves countless electrical connections, and the most sophisticated connectors I have ever seen to keep out condensation and ordinary rain splash. The connectors are not designed for immersion, and immersion causes water to enter the connector. Then, corrosion slowly sets in.

So these are basically "Jackass" videos.

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  • Yes and no. Your average car will NOT survive being submerged, but some hearty vehicles with jacked-up drive trains and a snorkel can because the electrical system was sealed to prevent water intrusion. No snorkel, highly unlikely it was sealed. – Machavity Feb 17 at 19:50
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** NOTICE ** I'm keeping this answer in place so as not to invalidate the educational comments associated with it. However the information I provided here is inaccurate and should not be used as reference. Pass me some of that humble pie.

This is a very basic answer. All engines need air to operate. Both fuel and air are mixed in the combustion chamber and ignited by the spark plugs. The air is pulled in through the airbox located on the top of the engine. A vehicle can be submerged underwater for a minute or so before water actually begins filtering through the airbox and into the combustion chamber. Once this happens the engine will simply begin to choke and eventually die (water and fuel don't burn). Those trucks and SUVs you see deliberately driving around under water have what's called a snorkel. A tube extending out from the airbox under the hood to the roof of the vehicle. This allows the engine to breath and prevents water from entering into the engine.

Now, if the vehicle stalls underwater (no snorkel) and it gets towed out, it can still come back to life (depending on how old it is). I'll use my 95 Pathfinder as an example. I flooded my engine once on accident, because I didn't realize how deep the water was. I pulled it out with a winch, let the water drain for about 10 minutes, then jumped in and began cranking it over. As I did this all the water in the combustion chamber (area between piston heads and spark plugs) began shooting out of my exhaust. After three or four cranks the Pathfinder started back up and away I went.

Now to answer your specific question, yes this can destroy your catalytic converter. Without going into detail, let's just say they're not designed to shoot water through them and leave it at that. As far as the spark plugs go, water wouldn't damage them. Once they dry off (during cranking) they're good to go.

All this being said, bear in mind that I did say this all depends on how old the vehicle is (older being more reliable). I seriously doubt you will ever see any vehicle made after 2001 going under water. Today's vehicles are filled with so many electronic items that you're likely to do thousands of dollars in damage simply by getting a bit of water spray under the hood. They definitely would not survive being submerged.

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    Part of your answer here is grossly inaccurate. The problem with the intake of water is not that water/fuel doesn't burn, it's that there is a high likelihood of the water coming into the engine causing what is called hydrolock (or possibly hydralock). Water doesn't compress. Get enough of it into a cylinder and it will cause your engine to stop suddenly. This can cause severe and even catastrophic damage to the engine, from which it will not recover without major surgery. When you say this can take minutes driving in water to happen, I'll tell you it can take seconds. Not a good thing. – Pᴀᴜʟsᴛᴇʀ2 Feb 14 at 13:38
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    There is no way your engines got water into the cylinders. If water got sucked in on an intake stroke, where would it go on the compression stroke? The water that came out of your exhaust was obviously just water that got into the exhaust when the exhaust was submerged. Fortunately for you the engines clearly cut out before sucking water into the cylinders. – HandyHowie Feb 14 at 22:03
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    @JoshCampbell when you think you flooded the two cars, its more likely you shorted the electrics which stops the engine running. Distributor caps are vulnerable to any moisture, a drop in the wrong place can stop the engine dead. Then a cooling fan blade resting in water can be enough to stop the engine starting (assuming crank-driven fan not electric) A hydrolock event in a petrol engine may be recoverable with effort, in a diesel its normally game-over for at least one piston/conrod. – Criggie Feb 14 at 22:37
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    I appreciate you guys taking the time to point out my misinformation. I have updated my answer. After performing several hours of research on Hydrolocking I was shocked to say the least. Not only does it appear that water in the combustion chamber can cause catastrophic engine damage, it can actually happen almost instantly. Given my new understanding of this I find it incredible that my Pathfinder survived. I now find myself asking the same question as the OP. Thanks again everyone. – Josh Campbell Feb 14 at 23:11
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    @Criggie Are you sure that a cooling fan blade in water will stop the engine starting? I can’t see that happening. The starter motor is connected to the engine by gears, whereas the fan is connected by small belt. I don’t think the extra load of a blade in water will have any effect. If anything, the belt will just slip. When you consider that the starter turns the engine and all ancillaries, I am pretty sure the fan will not stop it. – HandyHowie Feb 15 at 10:44
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Some vehicles, by their very nature, are more drive-able in deep water than others. Back in my young and exceptionally stupid days, I lived on a small peninsula that was surrounded on 3 sides by Long Island Sound, which is salt water. The main road that ran down the center of the peninsula had a low spot that was flooded twice a month during high tides, stranding all the residents for several hours unless they wanted to risk driving through salt water. My 60's-era Volkswagen Beetle had its engine in the rear, with its air intake and distributor up high. As long as I kept moving through the water at a brisk pace, the Bug would produce a bow wave in front and a deep void in the seawater at the rear, and I never stalled or got stuck. Water lapped up to the windshield on several occasions. (For the safety-conscious critics out there, this was standing water with no perceptible current and no chance of being swept away.)

Of course, after several years of twice-monthly salt water soaking, the car started to resemble a Fred Flintstone model.

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