When water leaks from under your car, it could be a sign of a problem with your engine’s coolant system. It could also represent a harmless part of the car’s daily running, such as the air-con, exhaust, or windscreen washer fluid residue.
The best thing to do is to use a flashlight to determine the source of the water. If you find a leak on part of the coolant system, provided it’s not leaking excessively, you should be safe to drive to your nearest auto shop. If the water is practically gushing out, it may be more sensible to hire a mobile mechanic.
This article will explain why water leaks from under cars and what to do about it.
- Is it water?
- Most likely causes
- Air conditioning system
- Exhaust drips
- Exhaust moisture
- Interior floods
- Coolant Temperature Sensor – How Can It Be Fixed?
- Oil In Coolant – Do You Have A Blown Head Gasket?
- Brake Fluid Flush Cost – A Price Worth Paying For?
- ECT Sensor Issues
What Is The Water That’s Leaking?
Provided it’s clear, the water is most likely to be just that – water.
If it’s anything other than water, this would be an entirely different question.
For example, the liquid underneath your car could be any of:
- fuel (gasoline or diesel),
- brake fluid,
- power steering fluid,
- transmission fluid,
- Ad Blue (in diesel cars),
- washer fluid,
- or engine oil (although you’d be pretty unlikely to mistake this for water).
If you realize that the leak is from one of these, you should follow different steps than those outlined on this page. Please see any of the following pages on Motor Verso for answers to your questions.
- Brake Fluid Flush Cost
- Brake Line Replacement Cost
- Check Transmission Fluid
- Transmission Fluid Change Cost
- Oil Leak Repair Cost
- Oil Smells Like Gas
- Power Steering Fluid Leak
Most Likely Causes Of Water Leaks Under Your Car
Often, this water comes from the air conditioning system. On any day when you’re using the system – especially a hot, humid day – all the excess moisture has to go somewhere. It leaves the car through a pipe, and this is what you’ll be noticing.
The water could also come from your windscreen washer fluid. Many people use a large concentration of water in the washer fluid tank. After using the washer fluid pump in your car, the water sprayed onto the windscreen starts to drip down to the ground. There could also be a crack in the washer bottle – check that the leak isn’t directly below it.
There are also a few other potential causes, such as moisture from the exhaust or a puddle of water sitting in your car.
Is It A Coolant Leak?
More seriously, although less commonly, a water leak could indicate a severe problem with your coolant.
Modern car engines are almost always “water-cooled”, as opposed to “air-cooled”. That is, the heat is removed from the engine through a liquid such as water passing by it, rather than air. Motorcycles and mopeds still use air-cooled engines to reduce engine bulk.
The “water” in modern engines is standard, pure water. However, it’s usually mixed with antifreeze, preventing the pipes from freezing up in winter and causing damage to components like the radiator. Combined, water and antifreeze are referred to as “coolant”.
Antifreeze/coolant is colored. Provided your engine has antifreeze in the coolant system, any water leaks should also be colored. Check your coolant tank to see the color of the antifreeze your car takes.
As long as the water dripping under your car is clear, you should be okay. However, double-check on the off chance that the system is running on pure water (with no antifreeze).
Why Is Water Leaking From Under My Car?
Suppose the water leaking from under your car is purely water. In that case, it’s most likely to be coming from the air conditioning system or the washer fluid, as mentioned above.
With the washer bottle, check it all over, looking for leaks. For slight leaks, you’re likely to notice drips balling up on the tank’s outside and perhaps dripping down the edge, so look for those. It could be something as simple as a stone having been thrown up and causing a crack.
Air Conditioning – Why Is Water Leaking From Under My Car?
When considering air conditioning, we need a whole section to itself.
Contrary to popular belief, the air conditioning doesn’t cool air down (although it’s very similar). Instead, it removes the heat and moisture from the air being sucked in. Without said heat and humidity, the air feels ice-cool.
Without going into too much detail on how the air conditioning system works, it’s vital to grasp a couple of concepts. The refrigerant in the system is a gas/liquid constantly flowing between hot and cold, high pressure and low pressure.
The system uses these pressure differences and two radiator-like components known as the evaporator and condenser to remove the heat and moisture from the incoming air. Part of the evaporator known as the evaporator core is what’s responsible for taking the humidity out of the air.
Removed moisture has to go somewhere – it can’t clog up the AC system. It drains out of the car through the evaporator drain. If it’s your air conditioning causing a water leak under your vehicle, this is where it’ll be coming from.
With water from an air conditioning evaporator drain, you shouldn’t see anything more than a flat layer of water on the asphalt surface. A “patch” of water, if you like. It shouldn’t be a deep puddle or any significant amount of liquid. If so, something may be wrong with your AC system, or the leak might be coming from somewhere else.
Is The Water Leak Under Your Car From Your Exhaust?
I’ve also touched on this issue in another article.
When you turn your engine off after a decently long drive, the exhaust starts to cool. This cooling condenses moisture in the air to form ever-so-slight puddles within the exhaust piping itself.
When you turn the engine on again, for example, in the morning, the condensed water evaporates again before re-condensing on the cold tailpipe. Thus, the water drips from the end of your exhaust pipe. This phenomenon touched on in the article linked to above is usually also accompanied by steam coming from the exhaust, often mistaken for white smoke.
To check if the water is coming from your exhaust, see whether the patch of water is developing underneath or near to the tailpipe. If so, you’ll likely be able to see water dripping from here, especially when someone blips the throttle. (Keep your hand away from it to avoid getting scalded.)
Water is also a product of the emissions-reducing reactions happening in the catalytic converter and so you should always expect to see water droplets of some kind anyway.
It could also be possible for a small water patch to form under a hole in the exhaust. When an exhaust blows, it’s usually down to rust or physical damage creating a small hole in the metal. You can hear when your exhaust is blowing because it makes a different noise – a sort of throaty, raspy sound. In theory, normal puddles of water developing within the piping could drip out any significant holes rather than from the tailpipe.
This may be the cause of the water leaks under your car.
How Do I Fix Water Leaks From Under My Car?
With an air conditioning system, you have nothing to worry about. The water you see leaving the car is a perfectly natural part of how the car runs. In fact, there’s actually more of an issue when you don’t see any water under your car.
If the leak is coming from your washer bottle, you may need a replacement part. It should be a relatively simple job, although formed plastic parts can be surprisingly expensive, so watch out for that. Of course, you could always try to patch it, but you should expect the problem to return relatively often.
With an exhaust pipe, there’s nothing you need to do unless there’s a hole – a “blow” – in the exhaust piping itself. Small holes can be welded, but eventually, you’ll need a replacement part.
How Do I Fix A Coolant Leak?
For a coolant leak, it’s a much bigger problem but still perfectly manageable.
First, you’ll need to identify the leak. Start by locating the coolant drips on the floor and then working upwards. It might be best to get underneath the car at this point, so make sure it’s in Park, and the parking brake is on. Safety first.
(Note: don’t rest your head in or anywhere too near the puddle – you’ll get coolant in your hair and, dangerously, coolant may drip into your eyes. It is worth wearing safety goggles for this.)
Usually, you’ll find the coolant leak in one of the rubber pipes, the reservoir (also known as tank or expansion tank), or the radiator. It might also be in other locations.
The water and coolant running through the system are almost certain to eventually exploit a tiny flaw, such as creating rust areas. Rubber pipes also become brittle over time and need replacing, while radiator clamps can lose their tension.
Whatever the cause for the water leaks under your car, that part will need replacing.
(Just to note, duct tape and a band-aid aren’t suitable long-term repair jobs! If you need to use “botch job” materials, it should be for a minimal time – only enough to get you to the nearest auto shop or home.)
To replace the faulty part, you’ll first need to drain the coolant system. If you don’t, coolant will start uncontrollably leaking everywhere as soon as you remove the component.
How Do I Drain The Coolant?
Before starting work on draining the coolant, you should make sure that the engine is cold. This is crucial because the coolant system is pressurized (note the warning sign on the radiator cap). If you try to remove this cap while the engine is still hot, you’ll get scalded by the hot water vapors escaping past it.
With that in mind, open the radiator cap. As shown in the video from Engineering Explained below, it’s a good idea to leave the radiator cap covering the gap it’s opened, as this prevents dirt and debris from getting in and damaging the system.
Put a pan underneath the car to catch the coolant and then loosen the drain plug. You’ll find this at the bottom of the radiator, and you’ll probably need to get down underneath the car to access it.
With the drain plug loosened, the coolant will drain out. There are often bits of chassis or engine components in the way of the coolant splashing down. Don’t worry if it’s not a clean stream of fluid – it usually isn’t. The coolant should be colored (with the color depending on the type of coolant your engine needs) as long as it was put in incorrectly.
Next, tighten the radiator drain plug and move the catch pan to remove the engine drain plug. This removes all of the coolant that was sitting in the engine. When replacing the engine drain plug, some people coat the thread with a high-temperature-resistant sealant to minimize leaks. It’s also always a good idea to replace the washer with a new one.
Make sure you tighten everything to the specified torques. See your owner’s manual for the exact details.
Finally, you’ll also need to detach and remove the coolant reservoir, draining its contents into your catch pan too.
With everything reinstalled, including the component you’ve had to replace for the water leaks from under your car, you can then add the new coolant.
Make sure you’re using a coolant (or antifreeze + water) that’s compatible with your vehicle. Again, you’ll find everything you need to know in the owner’s manual. With coolant, it’s also imperative not to exceed the MAX line on the tank as you fill it up.
With the reservoir topped up, you’ll then also need to add coolant to the radiator. Fill it up to the recommended amount in the owner’s manual.
Before putting the radiator cap back on, you need to purge the air from the system, so it works properly. To do this, start the car and leave it running for a good while – the video above recommends half an hour, although sometimes even longer is required. When you no longer see bubbles evaporate from the radiator, you can replace the cap.
Double-check everything is on correctly and secure, and you’ll be good to go!
Water Leaks Under Your Car Caused By Interior Floods
Sometimes, your car can take on water. Most commonly, people notice this when it is clear and obvious. For example, when water pools into the passenger footwell (a common fault on more vehicles than you might think), the trunk or down into the door cavities.
Over time, or in certain positions or locations, these water pools will drip and splash onto the ground below. When you notice water leaks under your car, you may be seeing something along these lines.
Check for damp areas in the cabin above where you’ve found the water leak.
If you discover that this is the problem, the best thing to do is to stop the water from getting in in the first place. For many cars, this is a common fault that will be addressed in many different ways across the internet and various books and manuals. If you’re in any doubt, however, a good mechanic will be able to take care of it for you. Don’t be afraid to ask.
How Can I Prevent Leaks In The Future?
Trying to prevent water leaks from under your car requires a little essential maintenance.
As mentioned before in this article, the chances are that you won’t need to do anything particularly special, in particular if the issue is simply the air conditioning.
The main thing to watch for is that your coolant system is in good condition. You can check this yourself or with a mechanic can do it as part of a regular service. If they notice any warning signs of corrosion, rust, damage, or premature leaks, they’ll let you know and advise you on the best course of action.
The coolant system does require maintenance, despite being something most car owners don’t think twice about (other than the coolant itself). The whole system needs to be drained to replace any part of it, whether it’s a pipe, hose, radiator, clamp, tank, or something else. You can then swap out the old component for a new one and refill it.
General regular maintenance also keeps your car, in general, in good condition. The more you look after, the higher your chances of the vehicle lasting longer in a better state.
Other than regular maintenance, simply watch for early warning signs of problems. It doesn’t have to be a huge effort; you don’t have to do a full inspection every day. But weekly or monthly visual checks under your bonnet and under the car will go a long way to preventing both this issue and many others.
Conclusion – Water Leaks Under Car
Water leaks under your car aren’t usually a cause for concern.
As a general rule, the more water there is, the more reason you have to be cautious. If the water is nothing more than a patch on the ground, it’s likely to be harmless and simply indicate that the car is working. However, you should still do your diligence and check engine components such as the coolant reservoir, washer bottle, and other fluids.
If the water does turn out to be a coolant leak, it’s best to seek expert advice. However, you could also always work on this yourself, as mentioned in the article.
Overall, don’t be too concerned about a water leak unless there are other clear signs of engine issues. If it’s paired with any of the following symptoms, I’d recommend turning the engine off and getting a tow to the nearest auto shop.
- Reduced fluid levels in the coolant expansion tank or brake fluid reservoir.
- Spiking engine temperature.
- Power reduction.
- Reduced fuel efficiency (increased fuel consumption).
- Lack of braking power.
I hope this article has been interesting and that you now know a little more about what might be causing water leaks under your car.