# Why can some cars go through water while others can't?

Why can some cars (mostly old Russian cars on YouTube) seemingly go through water while others can't? I'm talking about situations when the water level is at half the height of the car, so the engine is under the water. What are the differences between engines that break under water and those that don't?

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## migrated from physics.stackexchange.comMar 15 '13 at 14:28

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Hi Busky. Welcome to Physics.SE. I think the question is more likely a production, design or maybe an engineering (as you've mentioned). It's kinda off-topic here. I'll better wait for others ;-) – Crazy Buddy Mar 15 '13 at 8:32
I looked at stackexchange and didnt find better place ... There is "Electrical Engineering" site, but Im not interested in answer related to electricity (there may be short circuits), Im interested in mechanic differences in engines. – Buksy Mar 15 '13 at 8:39
In that case, you can wait for sometime, so that others (probably the mods) can help you ;-) – Crazy Buddy Mar 15 '13 at 8:46

driving through water could potentially do a couple of different things:

First off, if the water level is over the tail pipe, the engine rpm must be kept high in order to keep the exhaust pressure up, so that water does not go up the tail pipe and stall the engine. If this was to happen, it wouldn't likely do damage, but the car would have to be towed out of the water, and a modern car would likely throw a trouble code to the computer, causing the computer to have to be re-set. If you were able to drive through, then you didn't have this problem.

If the water level gets above the air intake while the engine is running, the engine could suck in water, and the engine could hydrolock, which means that water is sucked into the cylinders. Because water does not compress like air, water in the cylinders can cause severe damage that will require and engine rebuild or replacement. If water gets in the engine while the engine is stalled, the water will have to be removed before the engine is started or a hydrolock could occur. Remove the spark plugs and crank the engine, and the water will be pumped out of the spark plug holes. If your vehicle hydrolocked, you would know about it, because it would make at least one very loud bang, and would not continue to run. Since most air cleaners are near the top of the engine compartment, in most cases, the water would have to be more than a foot deep to allow water into the air intake.

Finally, if the water gets higher than the vents on your crank case, transmission, or differential, you could get water in your engine, transmission or differential oil. This would allow the vehicle to continue to drive, but over time, it could damage the vehicle. To check if this is the case, check the oil in each of these locations. if the oil on the dipstick appears milky, then there is water in it, and it should be changed. 4 years ago

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"older Russian cars" is the key phrase :) – HelloW Mar 15 '13 at 14:43
Don't forget about electronics, even just the distributor. Water (assuming it isn't pure H2O) is very good about letting electrons go places they shouldn't, usually to bad results. Now, if your car is an old diesel with mechanical fuel pumps, then you don't have much to worry about. – jwernerny Mar 15 '13 at 17:54
For example, in Audi Allroad with automatic transmission, when you put car in about 25cm of water, it can damage transmission control unit which is costly to repair. – Mustafa105 Apr 9 '14 at 9:48

No car is "waterproof" since it's need air at some point to run correctly, but you can make it more "water-friendly". My 1987 Toyota Land Cruiser have been modified to tolerate water crossing up to about mid-door. To do so you'll have to(non exhaustive list) :

• Raise your air intake as much as you can, mostly by using a snorkel
• Raise every breather (axle, transmission, transfer case) to avoid water mixing up.
• Make sure you do not have leak, both for the environment and so that water does not go through the other way
• Raise all electronics modules, I do not have that on mine but some friends with Toyota FJ Cruiser have their electronics under the driver seats, which could short everything and disable the truck

Then they are some technique that may come handy when crossing water, such as creating a small bow wave with a slow and constant speed, crossing slightly upstream, etc...

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Another problem to consider is that many cars are buoyant. Many cars have a passenger compartment that is sealed well enough to cause it to float. You would have to consider this aside from everything else. Even if you didn't have any problems with intakes, exhausts, electronics, and seals, you would still be in trouble if you got your car into a river and then your wheels couldn't touch the bottom.

That is why most humvees allow water into the passenger compartment easily, so that the truck will remain on the bottom of the body of water and the tires will have traction.

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Does the H3 do this as well? – timbo Apr 30 at 8:38

Safe water level is generally defined by location of air intake.

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Most modern cars including 4x4 have the air intake low down forward of the front wheel well which is far from ideal.A good rule of thumb (assuming you have raised air intake such as with a snorkel) is for a petrol vehicle at the appropriate speed you can safely negotiate water to half the height of your tyre-for a diesel to top of tyre.A car bra also creates a bow wave and prevents a lot of water intrusion.A cheap tarp and occy straps will do the trick

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