Why Does My Coolant Leak When Car Is Not Running?

There are a lot of reasons that can cause an issue of coolant leak when the car is not running. You have to form a habit of always checking your vehicle before you set out on the road; doing this will help you discover any problems or damages in your car on time. You should know that a vehicle’s coolant can normally reduce with time, and having a low-level coolant in the coolant reservoir or radiator is very bad for the vehicle as it can cause your vehicle’s engine to overheat.

When your coolant reservoir has a low coolant level, the engine will not have enough coolant to keep it an average temperature. Your vehicle’s engine temperature should not be more than 220 degrees. If this temperature is exceeded, it can severely damage your vehicle, something you do not want to happen.

Always pay attention to the signs and signals that indicate engine problems. A lot of vehicles have factory-fitted sensors that can notify the driver when there is a low coolant level in the cooling system of their vehicles.

coolant leak only when engine is cold

What causes the coolant leak when the car is not running?

A damaged Heater Core

When hot coolant is pumped to the engine through the heater core, the heat generated blows into your vehicle by the ventilation system when you put on the heater of your vehicle; if you have a faulty heater core, there will most likely be a coolant leakage under the passenger seat of your vehicle.

Torn hoses

The hoses responsible for carrying the coolant from your vehicle’s coolant reservoir to your engine might be broken if you experience antifreeze leak symptoms. Hoses help in transporting coolant to various parts of the vehicle’s cooling system. If this component is faulty, it can affect engine performance due to cooking leakage. The hoses can get damaged due to exposure to heat and long-term use, especially if your vehicle is used for frequent long trips.

A torn radiator hose can also cause a stoppage in the flow of coolant from the radiator to the reservoir due to leakages.

Faulty head gasket

If you discover coolant leakage below the exhaust or intake manifold gasket, it can result from a bad head gasket. The head gasket enforces an easy flow of oil and coolant in your vehicle’s engine system. A blown head gasket can negatively affect the combustion chambers, which is very dangerous to your vehicle, and this damage can cause coolant leakage under your vehicle.

Damaged radiator cap

The radiator cap ensures that the coolant in your vehicle’s radiator does not flow out, and it keeps the coolant at the right pressure inside the radiator. When there is a damaged radiator cap, there will be a coolant leakage, causing a low coolant level in the radiator. Also, if you have a bad radiator cap, it can tear the radiator hoses as a result of accumulating high pressure in the hoses. This type of damage can cause the coolant reservoir to overflow.

Bad intake manifold gasket

When tackled with a bad intake manifold gasket issue, you can experience coolant leakage from the gasket located inside the intake manifold where it connects with the engine of your vehicle. This can be one of the causes of coolant leakage under your vehicle, and this kind of fault should be repaired as soon as possible in order to avoid further damage.

Bad water pump

There can be severe coolant leakage if you have a damaged water pump in your vehicle. The water pump facilities the smooth flow of coolant through the hoses of the engine block and radiator. If this pump is damaged, you will notice serious leakage of coolant from your vehicle.

A faulty coolant reservoir

A faulty or overflowing coolant reservoir can be taken as one of the causes of coolant leakage from your vehicle. When the coolant in the reservoir is full, there will be a release of excess coolant, which might appear as a leak. Hence, you have to properly check the cause of the issue instead of replacing the reservoir due to a false assumption.

How do I locate a coolant leak in my vehicle?

Detecting the cause of coolant leakage can prove difficult due to the nature of the engine system. That’s why I use the JIFETOR Radiator Pressure Leakage Tester to properly diagnose the causes of coolant leakage in my vehicle, and it works perfectly. Areas that should be checked include;


Take a thorough look around the radiator and check for any fluid stain around it. Remove any dirt or debris on it to help you properly check if this might be the cause of the leakage.

Radiator cap

Also, check the radiator cap for any damages. You can remove it from the radiator if removable, for a thorough check and later fix it back to the radiator. Please do not forget to fix the radiator cap to the radiator; the consequences are severe.


Check around the visible hoses of the cooling system of your vehicle. If any of the hoses is torn, you will notice the presence of coolant on its surface. Also, properly check for cracks around the hoses; if there are cracks on a hose, it can also be a medium of escape for coolant; this can be one of the causes of coolant leaking from the bottom of the car.

Examine under vehicle

If you observe coolant flowing from under your vehicle, the coolant color can either be red, green, or blue, depending on the brand. You will need to view under your vehicle to see where the coolant is dropping from; this will help you streamline or easily locate the actual cause of the problem.

Head gasket

You need to check the head gasket for any leaks. If you discover leakages under your exhaust or intake manifold gasket, it is most likely due to a damaged head gasket. Also, check around the head cylinder and engine block for any coolant stains.

Heater Core

If you notice coolant stains on your vehicle’s passenger seat floorboards, you need to check the heater core immediately. A damaged heater core can cause the reason for antifreeze leak under the car’s passenger side.


The thermostat or thermostat housing is one of the major components to also check for leaks. A damaged thermostat can be the cause of a coolant leak when the car is not running.

How to fix a coolant leak when the car is not running?

After locating the causes of the car leaking antifreeze when parked, you also need to know how to fix this issue so you can save money that could have been used for repairs.

coolant leak fix

If you have a leaky radiator, you can try applying a cooling system sealer to stop the leak. If it is not a severe leak, the sealer will stop the leak for a long period. In a case of a severe leakage from the radiator, you will have to separate the Heating, Ventilation, and Air Conditioning (HVAC) case to change the heater core.

In a case of a damaged heater core, you can replace the original heater core made of aluminum with a copper heater core in order to reduce cost; this type of heater is durable and will still be able to function effectively.

When the problem is a punctured or cracked coolant reservoir, you can fix it with a silicone sealer. Apply the silicone sealer on and around the punctured surface. This can help seal up the hole. But if this process does not work, you will have to change your vehicle’s coolant reservoir.

To successfully change a coolant reservoir, you have to first remove the hoses of the coolant pressure and coolant reservoir. Remove the mounting bolts, then the electrical connector. After that, reconnect the electrical connector to the new coolant reservoir. Fix the coolant reservoir back into the system and reconnect the coolant hoses.

The only available option to solve the case of a damaged water pump is to replace the damaged water pump with either a remanufactured water pump or you can purchase a new one. To replace a water pump, you need to follow the following steps. It is also advisable that you also follow the manufacturer’s guide:

  • Detach the belt drive components of your car.
  • Gently remove the hose connected to the water pump.
  • Then remove the old water pump by losing its bolts.
  • Check the other components of your vehicle’s cooling system for any damages.
  • Carefully install the new water pump. Apply sealant, if recommended.
  • The bolts can now be tightened, and then fix the hose connected to the water pump.

For a torn or worn-out hose, you can either tighten the hose clamp or use rubber cement or hose repair tape to fix issues of small leaks; in this case, you do not need to change the entire hose. In case of severe leaks, you can carefully cut out the torn area, remove the bolts on the replacement coupler, and fix the cut ends of the hose to the clamp mender. Then fasten the bolt until the clamp is well-tight. You can continue tightening the connector until there is no leakage.

What will happen if I do not fix the coolant leak when the car is not running

Failure to fix coolant leaks in cars will lead to several issues even when the car is running. These issues include;

Engine overheating: Since the engine coolant is responsible for keeping the engine at normal operating temperature if the coolant leaks below the recommended level, it’ll cause the engine to overheat. Overheating can crack or warp the cylinder heads, which will drop expensive repair bills on the table.

Corrosion and rust: Engine coolant has an anti-corrosion agent that prevents rust and corrosion in the engine block and the cooling system components. If the coolant leaks out, it’ll expose the metal parts of the cooling system components to moisture. This will invariably cause corrosion or rust in the affected regions.

Other issues: We all know that engine coolant is a cooling agent in the cooling system. But what you do not know is that it can also serve as a lubricant. Coolants lubricate seals and gaskets in the cooling system units, preventing them from drying or becoming bristle. If the coolant level drops due to leaks, it will cause failures in the seals and gaskets.

Why is My Car Losing Coolant? YouTube

Frequently Asked Questions(FAQs)

Q: Will the coolant leak when the car is not running?

It is possible to have a coolant leakage when your car is parked. This can happen due to a damaged component(s) in the cooling system of your vehicle. It can be due to a torn hose, a bad radiator or radiator cap, or a damaged water pump or head gasket. Sometimes, this problem can occur as a result of an overflowing coolant reservoir tank and not the fault of the components in your vehicle’s cooling system.

Q: Why is my vehicle leaking antifreeze but not overheating?

The extent of antifreeze leakage determines if your vehicle’s engine will overheat. As long as there is still enough coolant to reduce the temperature of your engine, it will not overheat. But if there is a continuous leakage, it can lead to an extremely low coolant level, which will cause the engine to overheat. A bad hose or radiator can be one of the causes of this problem.

Q: Why does my car leak coolant when I turn it off?

There are several factors to consider that can be responsible for this problem. However, this can either be due to a broken component in your vehicle’s cooling system or an overflowing coolant reservoir tank. You need to check the components of your vehicle’s cooling system for any leakage, such as the radiator, head gasket, water pump, radiator cap, or thermostat.

Q: Can low coolant cause a leak?

A low coolant level in your vehicle’s coolant reservoir or radiator can cause your engine’s temperature to rise to a very high level. This can damage various components of the cooling system. If this happens, it can lead to a severe coolant leakage from under your vehicle.

Q: What signs indicate a coolant leak in my vehicle?

Antifreeze leakage from under your vehicle, white smoke from the exhaust, the low coolant level in your radiator, and discoloration of the radiator are among the common signs that reflect coolant leakage from your vehicle.

Q: What is the cost of fixing a coolant leak in a car?

If you notice a coolant leakage problem in your vehicle on time, it might be due to minor damage. It will cost about $90 to fix the problem. But if you ignore the problem and it causes major damages, it will cost about $700 for repairs.

Final Words

So that’s it for now. I am sure this article has been able to educate you on the subject of coolant leaks when the car is not running. Now you are aware of this problem’s causes if it happens to your vehicle and how to solve them by yourself. If you don’t understand some areas we talked about, feel free to back to us at any time, and we will always be at your service.

Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

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