What Can Happen If Your Exhaust Pipe Is Submerged In Water?

If you happen to live in hurricane territory, you've probably heard the advice that you're supposed to run from water, and hide from wind. Floodwaters are far more dangerous than they appear. Just 6 inches of fast-moving water can knock a person off their feet, and a foot or two of water is enough to carry away most vehicles. The danger isn't just the depth, it's the force. Floods can sweep up debris, conceal sinkholes, and cause sudden road collapses, putting both people and cars at serious risk.

Even if you don't live in a coastal flood-zone, flash-flooding, and water main breaks can happen almost anywhere. A heavy summer downpour is all it takes to turn a low-lying road into a potential trap. If you're the type that likes to go off-roading, you're probably aware that those muddy puddles aren't always what they seem. What appears to be a shallow pool could be deceptively deep. So what can happen to your car, particularly your exhaust system, if it becomes submerged in water? Here's a hint: unless your vehicle is an off-road truck equipped with a snorkel — such as this Ranger Super Duty from Ford Australia — none of it is good.

If your exhaust pipe goes underwater while the engine is running, you might get lucky — briefly. But if the engine stalls or shuts off, water can back up into the system, leading to rust, sensor damage, or in worst-case scenarios, catastrophic engine failure from hydrolock.

When your car is running, the engine's exhaust gases are pushing out with decent force. That positive pressure can keep water from entering the tailpipe for a little while. If the engine is idling and the tailpipe goes under, water may not immediately enter, especially in newer vehicles with tight exhaust systems. That's why it's usually not a huge deal if, let's say, you're backing your boat trailer into the water at the launch and your tailpipe is briefly submerged.

However, this only works as long as the engine stays on. As soon as the pressure stops, like if the engine stalls, shuts off, or your battery dies, water can back up the exhaust tract quickly. Hydrolock happens when water enters the cylinders through the exhaust or intake system, and the pistons try to compress it like air, which they just can't do. That water can bend connecting rods, crack cylinder heads, or seize the engine entirely. This kind of engine damage is often instant, catastrophic, and not always repairable. If it is repairable, it'll cost you thousands.

Even if you drove through water and everything seems fine, that doesn't mean you're in the clear. Water intrusion can take time to show up as corrosion slowly forms inside the muffler, catalytic converter, or sensors long after the submergence. This is something to keep in mind if you're buying a used flood-damaged car.

What happens if your car was parked during a high-water situation? If your tailpipe is underwater while the car is off, it's essentially an open door. Even if you've invested in rust-proofing for your car, nothing will save the interior components. As water slowly creeps in, it can fill your muffler, creep up the exhaust piping, and in some cases even reach the engine, especially if the vehicle sits submerged for hours or days. 

If water gets trapped in the exhaust system, it can lead to rusted-out components or failed emissions systems. O2 sensors, for instance, can get fried and start triggering check engine lights days or weeks later. That dirty water carries all kinds of nasty toxic chemicals, and even sewage — junk you definitely don't want in your car's internal components.

If your vehicle gets flooded, even partially, there is a strong possibility it will be declared a total loss by the insurance company. The expense of repairs is just too great. Even stranger, if your vehicle happens to be electric, there's a possibility that exposure to saltwater can cause it to burst into flames. When saltwater comes into contact with the lithium-ion battery, it can corrode the internal components and create a chemical reaction that causes dangerous short circuits.

Your exhaust system works by creating a one-way flow of exhaust from the engine, through the catalytic converter and muffler, and out the tailpipe. It's designed for combustion byproducts, not water. Unlike air, water doesn't compress, so when it enters from the outside, the entire system becomes vulnerable.

If you absolutely have to drive through water, keep it shallow, ideally no more than 6 inches, max, and try very hard not to stop. Even pausing at a red light or stop sign can let water creep up into your tailpipe while your engine's idling. Idling in water is one of the fastest ways to end up with serious engine damage. 

If your car stalls out in water, resist the urge to crank it back up. The smarter move is to tow it out, straight to a repair shop to be inspected for water ingress. If your tailpipe dipped below the surface, even briefly, and you're unsure how deep it was or how long it stayed submerged, don't assume everything is okay. Water damage often hides until it's expensive.