Why Does My Coolant Reservoir Keeps Emptying? Causes and Actions

Running a car with a working engine lets out heat. To regulate this heat and maintain temperature coolant comes into play. Coolant reservoir(aka. expansion tank) in the car makes sure there is no overheating of the engine that can otherwise cause serious damage.  

Typically the 195 to 220 Fahrenheit (approx. 90°C) is considered ideal but beyond that temp there can be problems.

But, sometimes the coolant reservoir (expansion tank) keeps emptying. If you have been a keen driver, there would be times when you question yourself about why my coolant reservoir keeps emptying. This article is all about that.

Now let’s find more information to solve the persistent problem. 

Coolant Reservoir in Cars

You can easily see near the radiator as a storage container with the clear plastic design.

It works to absorb heat to regulate its temperature in the engine compartment. The coolant stored in the reservoir circulates and everything works fine, but the moment coolant level drops, it causes overheating in the engine.

Low level of coolant in the coolant reservoirs will cause overheating issues in the engine which can also lead to damage such as blowing your water pump, head gasket, and cylinder head. Sometimes the damage can be irreversible.

Related: How Long To Run Engine after Adding Coolant

6 Causes of Empty Coolant Reservoir 

The leakage is the main reason why the coolant reservoir keeps on emptying. The issue can be with hoses, radiator, water pump or gasket. So carefully inspect to know what’s wrong. Here are the 5 causes that empty the coolant reservoir no matter if you have just filled it.

1. Puncture in the Radiator

Another reason for emptying the coolant reservoir is the hole in the radiator. Usually, most of the leakage in the fluids happens due to damage in the container. So if the radiator has a hole, there is no doubt why the coolant keeps on emptying in the car engine.

The hole or damage in the radiator can be due to a hard collision of the vehicle or maybe it has come to its durably concerns. Usually, when the radiator has become worn-out due to aging, it will start to degrade. You can also opt pressure testing  to check possible leaks in the coolant system. For pressure testing, take your vehicle to the mechanic.

2. Water Pump Seal is Faulty

If the water pump seal is faulty, the coolant in the reservoir will leak. For that you should keep a check on regular inspections to satisfactory performance. If there are any cracks, or the pipe has hardened, replace it. However, you should opt to replace the seal as well as the pipe for the best solution. 

3. Fault in the Head Gasket

The head gasket is there between the oil return passages, cylinders and pistons, sealing the coolant passage. 

When it has faults, it prevents those channels from keeping up with the seal, here the coolant in the reservoir starts to leak. You will notice following signs, rush to the mechanic;

  • Oil with a white, cloudy, or milky look to it
  • Watery leakage from your tailpipe
  • White smoke coming out of your tailpipe
  • A bubbling effect in your coolant reservoir, radiator, or both
  • Engine power loss (a possible result of low cylinder compression)
  • Overheating engine

4. The Coolant Hose is Leaking

If the hose is leaking you can tighten it with a new bolt or clamp. Replace the hose of the coolant if you find any leakage. Also check the head gasket for any leakage.

5. The Radiator Cap is Damaged

When the radiator cap is damaged, the coolant will not store in the reservoir if the radiator cap is cracked, broken, or it is not fitted correctly, there can be leakage that is emptying the coolant. 

The broken cap in the coolant reservoir will cause the coolant to evaporate, making the level minimal to zero. Hence, all you see is the empty coolant reservoir even after fill-up.

6. Overheating engine and Air in the Cooling System

Air in the cooling system will not cause leakage but it will cause interruption to the coolant circulation. Therefore, if you notice air in the coolant, you need to opt for bleeding of air to ensure its performance.

However, if the engine is overheating, it causes the coolant to evaporate. Therefore you notice early emptying of the coolant. The engine overheating can be for a number of reasons, one such reason is a malfunctioning thermostat.

Symptoms of Empty Coolant Reservoir – Here’s the Diagnosis

If you are unsure about coolant leakage or how to spot if it’s getting empty, here is how you should find it out.

  • If the coolant in the engine is low, it’s one of the signs why the coolant reservoir is getting empty. To check, open the hood of the car and find out the level of the coolant. If it’s low, top it up.
  • The leakage in the coolant will certainly empty it. Check out if there is any leakage in the coolant system, if there is any cracks, small hole or damage in the coolant reservoir, immediately get it repaired
  • If you are unsure if coolant is empty or not, check on the dashboard of your car, if it’s reading high engine temperature, it means the coolant reservoir is now empty. 

Sometimes it can mean that coolant isn’t circulating adequately. The coolant may also have a hard time in regulating the temperature of the engine.


What happens if you keep driving with the coolant reservoir empty?

If you drive for a few miles, it may not cause any adverse effects. But as you know coolant in cars makes sure the engine is cool and the temperature is under control, so if you drive farther, it can cause damage to the engine. 

Certainly, if you keep on driving with the overheated engine, you cannot expect no damage and all safety of your vehicle.

How far can I drive with low coolant in the reservoir?

Things become instantly vulnerable when you have low coolant in the reservoirs. If you mean that low coolant is still above the minimum mark, you can drive for a few days. But if it’s below the minimal mark, avoid driving till you get it filled. Otherwise there can be serious engine damage due to overheating.

How do I stop my coolant from leaking?

This might sound usual, but regular maintenance of your car saves it from most of the potential damage. As you see, coolant leakage happens due to damage of hose, gasket etc to make sure everyone is working in order.

Also follow the car maintenance that also includes changing out the coolant so that its level remains maintained.

How do I check coolant level?

Turn off the engine and let it cool. After that, open the car’s hood and look for the coolant reservoir (in a clear plastic bottle). The level should be between F (full). If it’s at the L (low) side of the coolant reservoir, top it off.


There are multiple reasons to empty coolant reservoirs. So you need to carefully inspect the solution. But it’s highly important to accompany yourself by a professional while inspecting. We suggest you take your car to the mechanic if you don’t know about the head gasket, or how to check the engine.

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