why can combustion cars stop working after driving through flood waters but be okay in heavy rainfall?


I’ve recently seen on tiktok lots of footage of nice cars driving through flood water, usually they accelerate into it and there’s a surge of water back onto the bonnet but at first thought this seems like the same thing that happens when it rains

In: 0

ICE have an air intakes. When water reaches the air intake it floods. Rain doesn’t enter the intake, so no flooding

Deep water floods the air intake. Water then gets sucked into the engine intake, and into the cylinders. Once in the cylinder it causes hydro lock because the pistons can’t compress the water that has entered. This basically destroys the engine

Literally same way you can drown in water, yet don’t drown in the rain. It’s a 1 to 1 exact analogy. The engine doesn’t fill up with rain water when taking in air the same way your lungs don’t when your face is lashed with rain.

But submerge either, and it definitely will.

This is an issue of both placement and amount.

The internal combustion engine requires both gasoline and air to work properly – gasoline as a liquid if you fill up the cylinders in an engine with it, won’t make the engine run, but it has to be sprayed in a mist and mixed as droplets suspended in air.

To that end, cars have air intakes that lead directly to an otherwise-sealed engine.

When air gets mixed with the gas, it explodes and drives pistons.

When water gets mixed with gas, nothing goes boom, the engine stalls, and your oil gets water on it which can cause damage (since water on its own is nowhere near the sort of lubricant that motor oil is)

Even in heavy rain, the fraction of air that’s occupied by water (the falling drops) is roughly 1 part per million, leaving plenty of air to burn. In comparison, flood waters are almost entirely water, leaving no air to burn. Cars can keep the raindrops out by keeping the air intake under cover but normal cars (those without snorkels) will suck water once it’s too deep.