Coolant Reservoir (Functions, Symptoms, Leak & Repair)

You are not the only one puzzled by your car’s coolant reservoir. You may find many familiar parts on your car’s hood or a maze of wires and pipes that you don’t know what you are looking at. You’re not alone if you feel this way.

Even the most experienced mechanics can specialize in one type of vehicle or even a specific year range. If they are presented with a car that they don’t know much about, they may be just as confused.

Here you will find everything you need to know regarding your vehicle’s coolant reservoir.

The engine’s temperature affects the coolant requirements. When it is cold, the coolant reservoir pressure is lower and it requires more coolant.

However, when the coolant reservoir pressure is higher when it is hot, the coolant consumption is reduced.

What Does A Coolant Reservoir Do?

What Does A Coolant Reservoir Do

Your engine burns fuel as it runs. It produces significant heat while doing this. The engine’s temperature can be raised above a certain point and can cause severe damage to the cylinders. This could lead to warping or cracking of the head gasket.

Overheating can cause car damage that is messy and may lead to the car breaking down. It is possible to repair the damage, but it can be costly to replace the parts.

The cooling system in your car works in order to remove heat from the engine and prevent any damage. Your engine’s coolant fluid is circulated through the cooling system via pipes.

The coolant is converted into gas by the engine’s latent heat, and as it passes through the car’s radiator, it becomes a liquid and heats the outside.

The coolant reservoir plays an essential role in the cooling system. The coolant reservoir stores excess coolant fluid until it is needed and is connected to the engine by the radiator’s hose.

The coolant reservoir is usually found in a transparent plastic container.  You can also only add coolant into your car’s engine via the reservoir and not directly into the radiator.

The pressure inside the radiator increases as your car heats up and the radiator cap lets coolant escape from the reservoir to relieve pressure.

The excess coolant remains in the reservoir until the system cools enough to cause negative pressure and pulls the excess coolant from the reservoir back into circulation.

Your coolant reservoir should be at least 30% full when the engine is turned off.

A leak in the coolant reservoir, or any of its attached hoses, is the most common reason why a vehicle overheats. Leakage means that coolant will slowly evaporate, and the system will eventually run out of coolant.

Check the coolant level of your regularly to prevent your car from overheating. You should pull over safely and switch off your engine if you notice smoke coming from the engine; the best thing to do at this point is to park safely and shut down the engine.

An overheating engine can cause severe damage if left unchecked.

Also Read: What Does A Harmonic Balancer Do?

Signs Of An Empty Coolant Reservoir?

Coolant Reservoir

Knowing what a coolant reservoir is and how it keeps your engine cool will help you understand why it is essential to maintain it in top condition.

An empty coolant reservoir can cause engine problems which in most cases could cause significant engine problems.

You need to be aware of some signs that will indicate that your coolant reservoir has run dry. Watch out for these signs at all times to ensure that you don’t get in the unfortunate situation of having no coolant in your vehicle.

So What are some of the signs that will indicate that your coolant reservoir is empty? here are just a few of them:

  1. When you open your hood, there is no coolant in the coolant reservoir.
  2. You notice that your car’s temperature gauge is telling you that your coolant is too hot.
  3. If coolant is leaking from your car’s engine, it may be a sign that your coolant reservoir is emptying.

These trouble signs should not be ignored. You could end up driving around with your coolant reservoir empty if you ignore them. This is the most dangerous thing you can do to your vehicle.

It could cause engine problems. It’s essential to determine the reason your coolant reservoir is empty before you can proceed.

What Should You Do If Your Coolant Reservoir Is Empty?

If your coolant tank is empty and you open your car’s hood, the first thing that comes to mind is to refill it with coolant. This is not the best way to go in all cases.

The new coolant may work temporarily, but it won’t solve the problem. It will only give you a false sense of security.

Instead of filling up your coolant reservoir, take your vehicle to a mechanic. They can determine why it is empty. The mechanic should identify the leak in your cooling systems that is causing your coolant reservoir to become empty.

Symptoms Of A Bad Coolant Reservoir

A bad or failing coolant reservoir can cause various symptoms that will alert the driver to the problem and need to be addressed. These are just a few.

1. Car Is Constantly Low On Coolant

A need to add coolant constantly is one of the most common symptoms associated with a failing or bad coolant reservoir.

The coolant stored in the reservoir can leak from cracks or become contaminated by small leaks.

Although the leaks might not be apparent to the driver, they can cause the reservoir to dwindle over time. A leak elsewhere on the engine can cause constant coolant demand.

It is essential to get it checked out if you notice this symptom.

2. Coolant Leaks

Coolant leaks are another sign that there is a problem with your coolant reservoir. Coolant leaks can occur if the coolant reservoir cracks, bursts, or is damaged by overheating or aging.

While small leaks can produce steam and drips, more significant leaks will cause streams and puddles and have a noticeable coolant smell.

Take your car to an auto service center if you notice this symptom.

3. Engine Overheating

Engine overheating is one of the signs of a failing or bad coolant reservoir. Engine overheating can be caused by a coolant reservoir that is not correctly holding coolant or properly pressurizing it.

This should be fixed as soon as possible to avoid any serious damage to the engine.

Coolant reservoirs are an essential part of the cooling system. If they become clogged, it can cause overheating or even engine damage.

If you think your coolant reservoir is failing, have it checked by a professional technician. The technician will determine if your car requires a new coolant reservoir.

Also Read: Ignition Coil Pack – Everything You Need to Know

How To Repair A Coolant Reservoir Leak

How To Repair A Coolant Reservoir Leak

Repairing a coolant reservoir leak isn’t as easy as cleaning your car’s interior. However, it is something you can definitely do yourself with the right knowledge and procedure.

Follow these steps to know how to repair a coolant reservoir leak.

1. Detect The Leak

Checking the coolant reservoir tank for leaks is the first step to fixing them. Wearing hoses and head gaskets could also cause coolant leaks.

Place a piece of large cardboard under your vehicle’s engine overnight to detect the source of your leak. On the cardboard, you will find the location of the leak.

To determine the source of the leak, you could also check your vehicle’s manual for your coolant reservoir location.

2. Remove Antifreeze From Coolant Reservoir

Once you’ve found the leak in your coolant reservoir, you can begin to drain the antifreeze out of the reservoir using a siphon.

It is important to remember that coolant systems should not be accessed while the engine is still warm. Before you start, make sure your vehicle is turned off and has cooled.

You can remove as much coolant as you want from the reservoir with the siphon. Once the coolant is removed from the reservoir, you can dispose of the rest.

During this time, you can also visually inspect the coolant reservoir for oil.

3. Mark The Leak

Next, locate the source of the leak on the reservoir tank. You can mark the location with a marker in black to make it easy to find later.

It is possible to locate the leakage in the coolant while draining it also.

4. Remove The Radiator Cap

Keep in mind that the coolant system is pressured. This is why you will need to take off the radiator cap before you can do this repair.

You could end up damaging your engine and possibly even worsening the problem by not cooling it entirely before you remove the antifreeze.

If your engine is still warm, the radiator could burst under the pressure of the radiator.

5. Disconnect Overflow Tube And Other Fittings

Now, you can remove the reservoir tank.

You will need to use a pair of scissors to move the clamp along your overflow tube. Then twist the tube to release it from the reservoir tank.

You may have other fittings that hold the tank in place. To locate them, you will need to refer to your owner’s manual.

After removing the fittings and the tube that was overflowing, you can now remove the reservoir tank.

6. Empty The Reservoir Tank Completely

The coolant leftover from the reservoir tank can be emptied into a container that you have kept.

Next, siphon the remainder of the coolant out. It would help if you used a disposable container such as an old milk jug or bucket, which you can toss away after you are done.

7. Wash Reservoir Tank

Before you can begin any repairs, the last thing to do is clean out the reservoir tank thoroughly, and This can be done with a water hose. Let it dry completely.

It may take up to an hour before you can start the repair.

8. Apply Epoxy

You can then mix Epoxy and use an applicator to apply it at the leak site. To fill the crack, press in the Epoxy. Let the epoxy cure or set according to the package instructions.

9. Insert Reservoir Tank

After the Epoxy has dried, you can put the tank back in your engine bay. Make sure you replace all fittings you took out when you took the coolant reservoir off.

10. Refill Coolant

To replace the coolant in the reservoir, use a funnel. Fill the reservoir to the required level, by adding enough coolant.

A line should indicate the fill point on the coolant reservoir tank.

11. Conduct A Radiator Pressure Test

After replacing the reservoir tank, you will need to reset the coolant system using a radiator pressure tester.

For about $50, you can find one at your local auto parts shop.

Here is a video showing you this procedure.

Frequently Asked Questions

Can I drive with an empty coolant reservoir?

Under no circumstances should you continue to drive your car if the coolant reservoir is empty. You might even not want to drive your vehicle to the mechanic’s garage if it isn’t right next to your home.

Can you just add coolant to your reservoir?

Add the correct coolant to your reservoir (not the radiator) if the coolant level is too low. Dilute coolant can be used by itself or in a 50/50 mix of concentrated coolant with distilled water. Once the coolant reaches the cold fill line, you can replace the cap and tighten the screw until it clicks.

Should the coolant reservoir be empty?

You might be wondering how much coolant my car needs when it is empty. At least 30% coolant should be in your coolant reservoir tank. The side of most reservoir tanks will have a min and max mark. 

How much does it cost to replace the coolant reservoir?

Coolant reservoir replacement costs average between $162 to $178. Parts are priced at $104. While labor costs can be estimated at $58 to $74, These prices do not include taxes or fees and may not reflect your vehicle’s unique situation. Other repairs might also be required.

What happens if the coolant is empty?

Your engine could overheat.
Coolant pulls heat from the engine. Without enough coolant, the engine can overheat and seize up. An engine that is too hot can cause permanent damage to the pistons.

Why is my coolant reservoir empty, but my radiator is full?

If the coolant in the reservoir isn’t returning to the radiator, it could be due to a leakage of the radiator hoses. These hoses allow fluid to flow from the reservoir to the radiator. A damaged radiator cap could cause this.


A Coolant reservoir is a plastic container that stores coolant in the engine bay of a Vehicle. Because engines are subject to cycles of absorbing and expelling coolant, coolant reservoirs must be available.

Coolant leaking from your cooling system will cause your car to heat up, which can cause severe damage to your vehicle’s engine.

To prevent coolant from leaking,  always ensure that your coolant in the reservoir is topped up. You can also identify the leak and quickly fix it so that you can return to driving your vehicle in a safe condition.

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