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Home / Symptoms / Car Leaking Coolant

Four common causes for a leaking coolant from the vehicle and their related parts.

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Is Your Car Leaking Coolant?

The coolant leak is commonly caused by a crack in the radiator, the heater core, or the coolant reservoir. The radiator commonly cracks if it’s old or if it hits an object. The leak can also be caused by a loose coolant hose, a faulty water pump, or even a blown head gasket.

Coolant is your vehicle's first protection against engine overheating; you're left vulnerable if it leaks. Checking your coolant levels regularly is a good practice since many leaks can strike unexpectedly. So, if you notice the levels dropping abnormally, something might be wrong.

Your cooling system requires routine maintenance. Coolant can turn acidic and eat away at gaskets and seals, causing dangerous leaks if neglected. In addition, factors such as temperature changes or simple wear can cause leaks.

Watch out: While coolant does incredible things for your car, it is a toxic substance. It can poison animals and waterways if it leaks from a vehicle. In addition, because coolant gets hot when it's working, it can also scald someone standing near a leak.

Let's Get To The Bottom Of It!

Does your radiator have corrosion or discoloration on the outside?

You may also see streaming coming from under the hood or notice the engine overheating.

The vibrations of driving, temperature fluctuations, and environmental stress around a radiator can cause wear on the seal that connects the tank that holds the coolant and the core. If a small leak develops, the coolant dries on the radiator. This dried coolant looks like corrosion and may show blue or red discoloration, depending on the color of the coolant.

Do you have a crusty buildup on the front of your engine?

You may also notice the engine overheating or feel a rough idle.

The bearings and seals inside the vehicle's water pump degrade with use. If coolant isn't maintained, it becomes acidic with age, speeding up the wearing process on these seals. In addition, when the seal between the pump and coolant leaks, it creates a weep hole that lets any coolant out before it affects the pump's bearings. This causes the leak to run down the engine block, which can be seen as a crusty, discolored buildup of dried coolant. Depending on the tank's coolant type, it may be red or green.

Do you have white smoke coming from the exhaust?

You may also notice that the engine cranks long before starting. After the engine runs, you might see a small puddle of coolant under the car.

Coolant passages between the head gaskets connect an engine's combustion chamber to the valve chamber. These passages dissipate heat from the engine block and the heads. Engine overheating or acidic coolant can damage the head gasket. When these gaskets are compromised, gasses from combustion get into the coolant passages, causing the coolant to become superheated. Superheated coolant leads to the engine overheating and further wear on the gaskets. Coolant leaks into the engine's combustion chamber when the gaskets are badly damaged, which you'll notice as white smoke in the exhaust. That's the coolant burning with the vehicle's fuel.

Do you smell a sweet smell coming from the air vents?

You may also notice that the windows stay fogged even when the defroster is on or that the carpet on the front passenger side floor is wet.

Inside the air box in your vehicle's dash is the heater core. This circulates coolant so that your heater warms up the vehicle's interior. If the cooling system isn't maintained, the coolant turns acidic and can degrade the heater core. This can cause coolant to leak inside the vehicle. In addition, if coolant gets in the air box, it gets vaporized by air blowing over it and through your vents. You will notice this vaporized coolant as a sweet smell blowing through your heating and air conditioning vents.

Does your coolant level keep getting low over time?

You may also notice steam coming from under the hood or your engine is overheating.

The coolant reservoir is the highest point of the cooling system and is filled with half air and half liquid coolant. When a leak in the reservoir occurs, the coolant won't be low in the tank until several heat and cool cycles force enough out. It is at this point that the low coolant is visible.

Do you find a puddle of coolant under the vehicle after it has been parked overnight?

You may also notice the "check engine" light is on or the "coolant temperature" gauge is running in the red.

The coolant hoses attach the engine cooling system to the radiator. Since they are made of rubber, they will become brittle over time and can crack, causing a leak. Flex from worn motor mounts can stretch the hoses as well. A band clamp attaches the hoses to the radiator or engine block. Wear over time and from temperature changes causes leaks. These leaks are most common after the vehicle cools when various components contract due to the temperature change. When your car is parked, it's cooling, and you will see the leak as evidence of this wear.

The most common causes for a vehicle leaking coolant

The most common causes for the car leaking coolant:

Leaking radiator: The radiator is one of the most important cooling components in your vehicle. It works by sending cold coolant to the engine and receiving hot coolant in return. Then, it cools the hot coolant just received, starting the process over again. The radiator relies on seals and hoses to keep coolant moving inside the system. If the radiator gets damaged, worn, or faulty, it'll allow coolant to leak out.
Faulty water pump: The water pump is the motor that actually pushes coolant, pressurizing it just enough so it can reach everywhere it needs to — the engine, radiator, hoses, etc. The water pump has direct coolant running through it, so if it gets any damage or sealing issues, it'll allow coolant to leak out.
Blown head gasket: The head gasket is a "barrier" that sits in the eye of the combustion tornado, between the engine block and cylinder head. The main role of the gasket is to keep the coolant from touching the oil, making sure the engine has enough of both fluids without cross-contamination. However, if the head gasket fails, these fluids might escape the system and leak out.
Heater core leaking: The heater core is the heater's version of a radiator that works by actually heating up the system instead of cooling it down. The core gets hot coolant from the engine to heat up your vehicle's interior. However, if the core seals or hoses fail, the coolant might start leaking out.
Leaking coolant reservoir: The coolant reservoir is a container that stores coolant. If this container gets damaged or its seals or hoses fail, it'll allow coolant to leak out.
Leaking coolant hose: The coolant goes through specific hoses that direct it toward the radiator, engine, etc. If any of these hoses cracks, gets loose, or develops bad sealing, they'll allow coolant to leak out.

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Frequently Asked Questions

Does your radiator have corrosion or discoloration on the outside?

You may also see streaming coming from under the hood or notice the engine overheating.

The vibrations of driving, temperature fluctuations, and environmental stress around a radiator can cause wear on the seal that connects the tank that holds the coolant and the core. If a small leak develops, the coolant dries on the radiator. This dried coolant looks like corrosion and may show blue or red discoloration, depending on the color of the coolant.
Do you have a crusty buildup on the front of your engine?

You may also notice the engine overheating or feel a rough idle.

The bearings and seals inside the vehicle's water pump degrade with use. If coolant isn't maintained, it becomes acidic with age, speeding up the wearing process on these seals. In addition, when the seal between the pump and coolant leaks, it creates a weep hole that lets any coolant out before it affects the pump's bearings. This causes the leak to run down the engine block, which can be seen as a crusty, discolored buildup of dried coolant. Depending on the tank's coolant type, it may be red or green.
Do you have white smoke coming from the exhaust?

You may also notice that the engine cranks long before starting. After the engine runs, you might see a small puddle of coolant under the car.

Coolant passages between the head gaskets connect an engine's combustion chamber to the valve chamber. These passages dissipate heat from the engine block and the heads. Engine overheating or acidic coolant can damage the head gasket. When these gaskets are compromised, gasses from combustion get into the coolant passages, causing the coolant to become superheated. Superheated coolant leads to the engine overheating and further wear on the gaskets. Coolant leaks into the engine's combustion chamber when the gaskets are badly damaged, which you'll notice as white smoke in the exhaust. That's the coolant burning with the vehicle's fuel.
Do you smell a sweet smell coming from the air vents?

You may also notice that the windows stay fogged even when the defroster is on or that the carpet on the front passenger side floor is wet.

Inside the air box in your vehicle's dash is the heater core. This circulates coolant so that your heater warms up the vehicle's interior. If the cooling system isn't maintained, the coolant turns acidic and can degrade the heater core. This can cause coolant to leak inside the vehicle. In addition, if coolant gets in the air box, it gets vaporized by air blowing over it and through your vents. You will notice this vaporized coolant as a sweet smell blowing through your heating and air conditioning vents.
Does your coolant level keep getting low over time?

You may also notice steam coming from under the hood or your engine is overheating.

The coolant reservoir is the highest point of the cooling system and is filled with half air and half liquid coolant. When a leak in the reservoir occurs, the coolant won't be low in the tank until several heat and cool cycles force enough out. It is at this point that the low coolant is visible.
Do you find a puddle of coolant under the vehicle after it has been parked overnight?

You may also notice the "check engine" light is on or the "coolant temperature" gauge is running in the red.

The coolant hoses attach the engine cooling system to the radiator. Since they are made of rubber, they will become brittle over time and can crack, causing a leak. Flex from worn motor mounts can stretch the hoses as well. A band clamp attaches the hoses to the radiator or engine block. Wear over time and from temperature changes causes leaks. These leaks are most common after the vehicle cools when various components contract due to the temperature change. When your car is parked, it's cooling, and you will see the leak as evidence of this wear.

Typical fixes to address the cause(s)

These are typical processes and repair services that fix a check engine light issue

The most common cause: Leaking radiator

The most common reason for a car’s coolant leaking is due to a radiator leak. The radiator is the "conversor" in your vehicle's cooling system that converts hot coolant into cold. This conversion happens because the radiator sends cold coolant into the engine; this coolant then heats up due to the engine's high temperature. Next, the now-hot coolant leaves the engine, returning to the radiator where it cools down again. The radiator relies on various seals, hoses, and protections to prevent coolant from leaking out. However, due to wear and damage, these seals can fail, allowing coolant to leak out.

Symptoms it causes: Apart from the coolant leak, you might notice engine overheating, smoke from the hood, burning oil smell, etc.
High risk of priority: The radiator is vital to keep your vehicle's engine from overheating. An overheating engine quickly damages various components and messes up the combustion process. In worst cases, the engine might overheat beyond safety limits and break down — or start a fire.

How exactly does the radiator start leaking?

Radiators are made to last close to a decade. However, they can wear out faster depending on driving conditions, accidents, misplacements, etc. Additionally, even though the radiator itself might not get cracks or damages, the connectors and sealings on it can become dry and damaged, allowing coolant to leak out. The most common reason a radiator leaks out is due to some kind of impact or accident in the vehicle's front, which is where the radiator sits.

Go safe: Ask for a mechanic to inspect your vehicle’s cooling system to investigate if the radiator is leaking due to surrounding components and if there’s further damage to check out. Many shops do transparent vehicle inspections and lay out your options after investigating your vehicle’s conditions.

What’s a vehicle inspection? It’s “detective work” on your vehicle, checking its systems to see if anything prevents the car from working as expected. In this case, mechanics examine different parts of your vehicle to track if anything is causing the radiator to leak. They’ll also check the condition of components during their inspection, noting which are causing the problem and which got affected by it, recommending to replace them in order of priority.

Transparency example in a leaking radiator service

A cooling system inspection is the most transparent process to understand why your vehicle’s radiator is leaking. This is because many components surrounding the radiator, coolant hoses, and engine can have a say in the issue, indicating the real culprits that caused it all.

Let’s read an example of how this kind of inspection helps to service a leaking radiator.

A customer dropped off their vehicle upon noticing some corrosion on the radiator. They thought the car's battery exploded, causing the problem.

The technician did not notice anything about the customer's concerns on the test drive.

During the vehicle health inspection, the mechanic noticed a lot of dried coolant on the upper tank of the radiator. The technician tested the battery and found nothing about the customer's concerns.

The technician used a cooling system pressure tester to pressurize the cooling system. They pumped up the pressure to the suggested rating on the radiator cap. Upon inspection, the technician found a small crack in the upper tank of the radiator that was causing it to leak coolant under pressure. The radiator requires replacement.

Leaking radiator

In this case, the mechanic put the “Immediate Action” tag on the radiator.

Similar Symptoms

Below are just a few examples of typical Symptoms and Fixes your car might be experiencing

Four common causes for a vehicle Leaking Oil and their related parts.

Is Your Car Leaking Coolant?

Let's Get To The Bottom Of It!

The most common causes for a vehicle leaking coolant

Find Professional Help

Frequently Asked Questions

Does your radiator have corrosion or discoloration on the outside?

Do you have a crusty buildup on the front of your engine?

Do you have white smoke coming from the exhaust?

Do you smell a sweet smell coming from the air vents?

Does your coolant level keep getting low over time?

Do you find a puddle of coolant under the vehicle after it has been parked overnight?

Typical fixes to address the cause(s)

The most common cause: Leaking radiator

How exactly does the radiator start leaking?

Transparency example in a leaking radiator service

Similar Symptoms

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Why Is My Evap System Leaking?

Why Is The Radiator in My Car Leaking?

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Why Is There Pink Fluid Leaking From My Car?