Tailpipes are mostly known for emitting two things: exhaust gases and sound. Both can be contentious issues, whether we’re talking about the president rolling back emissions standards or gearheads getting exercised over cheap exhaust sounds. But unless you’re driving something like a hydrogen-powered Toyota Mirai — which only emits (drinkable?) water vapor — you might not expect H20 to be dripping from your exhaust pipes.
And yet, it’s a common condition that’s considered normal for internal combustion engines running on gasoline or diesel fuel. That’s because water vapor is a naturally occurring result of a vehicle’s combustion process. Then, during the next step in the cycle, the leftover products of combustion are pushed out and into the exhaust system. Water molecules can be formed during the normal operation of a catalytic converter, too, as well as by condensation caused from engine heat in cold weather.
The bad news is that those aren’t the only reasons for water coming from your exhaust pipes. It can also be caused by serious engine issues that could put a real damper on your driving experience.
Water from a blown head gasket will suck the fun out of your day
Those drip-drip-drips from your tailpipes could also be telling you there’s a problem with your head gasket — and that can be a real wallet-killer. Replacement costs can be upward of $6,000 for swapping the gasket alone, and if your engine’s been damaged, you’ll likely have to replace that as well.
What’s so special about that gasket? It’s a carefully engineered piece of material that goes between the engine block and the cylinder heads, and its integrity is a key to your engine working properly. The engine strokes mentioned above cause extremely high pressures inside the cylinders, so if the gasket blows — meaning it loses its seal — it’s going to leak. And that can let coolant get into the cylinders, where it will be burned off with the fuel.
However, it will leave behind more water molecules to make the trip through your exhaust system. The good news is that it’s fairly easy to tell the difference between when water vapor comes from a healthy engine or when it comes from one with a head-gasket issue.
When you have to worry about water in your exhaust
You’ve got your car running and suddenly notice some kind of liquid leaking from your tailpipes. Now what? Well, one of the first things you should do is make sure any water dripping from your exhaust pipe is truly water. It’s okay if you get some black droplets, since the water may have mixed with carbon deposits on its way out, but the liquid should still feel and smell like water. If it feels greasy, that could mean it’s water mixed with fuel and/or oil, and that’s a symptom of a cracked block or head gasket failure.
It’s also worth keeping in mind that the regular water vapor from your exhaust can come out in thin clouds of white wispy steam that can easily be mistaken for smoke. Again, that’s normal. But seeing actual thick white smoke from your exhaust can mean trouble, and the same holds true for blue, black, or gray smoke, all of which can be the result of something getting into your tailpipe that shouldn’t be there. That’s when you should think about either getting your car into a shop or getting under the hood yourself.