Bubbles In Coolant Reservoir (Causes and Fix)

Vehicle cooling systems depend on a sealed connection of hoses to generate antifreeze/coolant all over the engine. These hoses are aligned in a loop that is sealed.

They allow the easy flow of antifreeze/coolant to parts like the engine block, head gasket, and cylinder heads so as to help keep the engine’s temperature right.

Bubbling and blockages could occur when there’s easy access to air into the sealed system, leading to overheating of the engine. Many reasons are responsible for air entering a vehicle’s cooling system. With the help of this article, you’ll know why antifreeze/coolant bubbles in a cooling system occur and how to sort them out.

How Does The Cooling System Work?

To know what brings about these bubbles, you first need to know how a cooling system operates. There are a number of parts in the cooling system of a modern vehicle. First, we have the water pump, which pumps coolants to an engine, and its various parts.

That right there is the center, otherwise known as the heart of a cooling system. Then we have the thermostat, which helps regulate a coolant’s temperature, so it doesn’t freeze or heat up.

Then there’s the radiator that helps reduce the temperature of the coolant after the coolant goes a lap about the engine. Making it perfect for cooling down the engine.

The radiator cap helps lock the pressure inside the vehicle’s cooling system because the absence of this pressure affects the freezing and boiling points adversely.

These parts send the coolant on a back-and-forth journey to pick up heat and then cool the radiator. This happens each and every time your vehicle is driven.

What Causes Bubbles in the Coolant Reservoir?

Most vehicles’ cooling systems are pressurized and require sealed hoses to dispense antifreeze/coolant throughout the engine. If this sealed system gets exposed to air, air pockets could build up and then cause blockages that could cause overheating and bubbling.

Bubbling, in this case, refers to the rising pressure of air in your cooling system, which indicates that an air pocket has interrupted the passage of liquid. A blown head gasket is one of the reasons behind it because the pressure of air in the cylinder heads has been transmitted to the vehicle’s cooling system. This released air brings bubbling in the antifreeze/coolant tank, which could be misunderstood as coolant boiling.

There are other reasons responsible for air getting into a vehicle’s cooling system, apart from a busted head gasket, reasons we’ll be considering shortly.

Also Read: How To Clear a Clogged Exhaust (Expert Guide)

How Do Bubbles Emerge In The Coolant Reservoir?

In the reservoir of the coolant, air bubbles erupt. Most vehicles’ cooling systems are compressed and use hoses whose systems are closed and allow for the free flow of coolant throughout the engine. The entrance of air into this system forms an air sac.

The flow of fluid is blocked by air pockets, resulting in an increase in temperature, thereby causing a boil, otherwise known as bubbles.

This foam can sometimes be considered serious and, other times, not so serious why certain movements could bring about the exposure of air into the cooling unit. While in other circumstances, the presence of air in that unit may require you to take out a part that is no longer working.

The level of air pressure in the reservoir is kept in a way that the coolant’s boiling level is increased.

So should there be a crack in the gasket or perhaps any other tube, the pressure will surely sneak out, which means the level of the boiling coolant will reduce seriously. And should this happen while you’re on the road in motion, there will be the release of white smoke from the engine.

Whether it is a cracked engine gasket, a bad pressure cap, or any issue, the effect could be fatal. So if there’s an escape of pressure from the reservoir, there will be a boil, resulting in the engine overheating drastically.

Though these bubbles come in different forms, neither of them is good for your engine. But being able to differentiate them will help you discover the fire behind these smokes.

Below are the types of bubbles you might find in your coolant’s reservoir:

Normal Bubbles

More often than not, air bubbles are usually located in the vehicle’s expansion reservoir. Funnily, the primary function of this expansion reservoir/tank is to take bubbles away from the vehicle’s cooling system.

Vehicle coolers work at their best without any air bubbles because coolants without bubbles tend to suck up heat faster than coolants with air bubbles. Because this helps prevent overheating of the engine.

Problem Bubbles

Bubbles in your expansion reservoir are expected, especially when your car engine isn’t so hot. But perhaps there are bubbles in the vehicle’s coolant; then it’s possible the head gasket is experiencing a leak. And to know if your head gasket is faulty, test all the cylinders in your car with a cylinder leak tester while the engine is off.

If these air bubbles show up while the rest is ongoing, they should be dealt with while the combustion products make their way into the cooling system. Because if unattended, your head gasket could go bad, leaving you stranded.

To be sure if you’re experiencing a leak, look out for any smell that smells pleasant. These smells have several explanations to them.

Some say this smell is that of maple syrup, while others say it’s that of butterscotch. That’s why it is advised to keep it out of animals or children’s reach because the smell of antifreeze could be mistaken for any of the above.

So, be on the lookout for such pleasant odors because your antifreeze might just be leaking away.

How Does Air Get Into The Car Cooling System

Bubbles In Coolant Reservoir

There are several reasons behind a bubble in your coolant. Here are some of the faulty parts that can cause the escape of air.

1. Blown Head Gasket

A blown head gasket allows the quick passage of air pressure from your reservoir tank and coolant tubes, which would result in a massive decrease in the boiling point. When that happens, a boil in the coolant brings about overheating in the engine.

The moment you notice a blow in the head gasket, immediately bring your vehicle to a halt to avoid causing permanent damage to the engine.

There are quite a number of things to tip you off that your head gasket is blown. Of course, the number one and most common symptom is overheating; though that’s a little difficult to discover, it’s still a sign.

Another sign is a bubble-filled coolant; this is noticed when you stop your car. You’d also notice the release of smoke from your exhaust and engine via the sides of the bonnet.

Because the combustion gas goes in through the cooling system via a cylinder head gasket that is leaking, the leak must be fixed. To get this done, take your vehicle to a good mechanic to fix the leak. And if you intend to save yourself a few bucks, you can repair it with some repair fluids for leaks.

If, after everything, the leak persists, the best and only option would be to change the head gasket. And to get to this head gasket, you’d have to take out almost half of its parts to reach your engine. It isn’t only tasking but quite expensive.

And if it isn’t fixed, it could cause irreparable damage to your engine.

2. Cooling System Pressure Cap

This cap is threaded into your cooling system after it’s been pressurized. The cooling system relies on this pressure cap to help retain the pressure inside and allow the free passage of coolant to the reservoir of the expansion. So if anything goes wrong with this cap or it gets replaced with an unfit one, the air is sure to leak out, threatening the safety of your car and your life.

There are a few symptoms to help you detect the reasons behind the leaks. First and foremost, be on the lookout for bubbles close to your pressure cap. Then there’s the overheating, which is another sign.

If the fault comes from your car’s pressure cap, it’s an easy walkover. However, endeavor to change to a pressure cap that your car’s manufacturers recommend.

3. Air Pockets

When antifreeze/coolant circulates throughout the engine, the air pocket on the vehicle’s radiator can get clogged. That’s the case when a coolant flush. And when the coolant gets added to the system but is insufficient to take out the remaining air, there might be an air pocket.

Signs to detect an air pocket are high-level temperature bubbles within the radiator that bring about overheating and also affect the radiator.

This problem isn’t entirely difficult to fix. All you need do is run the engine for about fifteen minutes until the air in the radiator dries out; then, you can now fit the pressure cap back on. Of course, this should also be done whenever your radiator is refilled, which is a little easier.

4. Faulty Thermostat

The work of the thermostat is to regulate the passage of coolant to and fro the radiator. This thermostat is expected to close at an expected time. It is also meant to be opened so as to drain hot coolant off the engine to the radiator to be cooled down.

Then bring it closer to the engine so the coolant can be heated up to start the vehicle. If the thermostat is faulty, its response time to when it opens and closes won’t be timely. Also, this would bring about bubbles in your radiator or coolant tank due to the pressure.

The signs here are constant as always since the air flowing there is unregulated; it will bring about overheating.

And as earlier stated, if you notice the emanation of smoke from your exhaust, especially white smoke, waste no time bringing your car to a halt. Though they might not mean a faulty thermostat, they sure don’t mean well, either.

The poor performance of the thermostat also affects the flow of the coolant. So it’s best to have it replaced with a supporting thermostat or an original one.

So provided the present thermostat is in good working condition, you wouldn’t have to worry about uncirculated coolant or air bubbles.

5. Faulty Heater Control Valve Or Hose

This control valve walks the hot coolant through the area of the passenger seat to keep it warm so the hot coolant doesn’t remain in the core of the engine for too long. A bad heater hose or valve could sneak air in, which could cause overheating and bubbling.

If you suspect any of the aforementioned signs, stop the vehicle immediately and call for a mechanic immediately because this is not an easy fix.

This doesn’t only affect your car but the passenger seating there as well because your vehicle’s heating function won’t work any longer. If this hose is loosed or worn out, it should be tightened or replaced, respectively.

6. Leaky Coolant Reservoir Hose

Note that the hose linking the coolant reservoir to the radiator should always be tightened. Radiator hoses that are worn out or perhaps damaged allow air through these hoses that, consequently, bring about bubbles in the coolant.

The coolant also finds a way to escape through these leaks from the reservoir hose, causing a decrease in the coolant level and overheating. In such cases, changing the hose is one of the best ways to have it fixed.

7. Faulty Water Pump

Coolant or antifreeze is circulated by a water pump through the pipes of the coolant and then flows via the engine pipes to the various components of the engine. If this water pump goes bad, air sneaks into this pump inlet. This air also reaches the coolant valve or radiator and forms an air bubble.

This water pump is meant to be closed at all times because when it’s properly closed, air will have no access to the pump. However, a faulty cap could have air trapped inside the pump, so it’s best to have this cap changed to prevent the passage of air.

8. Rust And Contamination

Like subsequent metal components, the radiator tends to rust in the cause of time. Peradventure, the radiator is not regularly cleaned, and the right amount of coolant isn’t supplied; dust is still sure to accumulate there. This is where dirt, rust, and other debris block the radiator tubes and negatively affect the efficiency of the water pump and thermostat.

High-level heat fires up the coolant, which brings about air bubbles.

When this coolant is stretched to some extent, it gets contaminated with certain build-ups like dust, sludge, and other particles. These particles block the radiator and other components connected to it. To avoid this clog, constantly flush the coolant reservoir or radiator and have the coolant refilled with a new one.

Also Read: How Much Does Coolant Leak Repair Cost?

How to Fix Bubbles In Coolant Reservoir?

It’s common knowledge that one of the best ways to fix a problem is by tackling its root. The question now is, what angles should be focused on and what steps should be taken when the reservoir of the coolant has bubbles?

1. Allow air pockets to escape after refilling the coolant.

The air tends to get stuck in the coolant system when refilling and to flush the radiator or coolant reservoir. In other words, you’re to make sure that that air does not remain there after the refill and flushing process.

To achieve this air extraction, turn on the engine for about fifteen minutes without the radiator cap on it after the refill. This exercise will help dry out every air left in the reservoir or radiator. After which, replace the cap and make sure it’s tightened properly, so air doesn’t get in.

2. Replace faulty thermostat

The coolant’s efficiency relies on the thermostat, so a faulty thermostat means a poor flow of coolant, which brings about a boil. To prevent this, change the thermostat with a compatible aftermarket thermostat or an OEM.

3. Fix a leaky head gasket

Because a leaking head gasket releases combustion gas into your cooling system, it’s expected of one to seal up every leak. To get this fixed, you can either do it yourself at home with some leak repair fluid or, better still, have a mechanic do it for you. But if this leak persists, it’s best to consider a new head gasket.

The head gasket’s position in a vehicle requires the dismantling of almost half the car engine. In other words, getting this fixed is going to cost a little more than just a little. This is why you shouldn’t let the repair get to such an extent, and be prepared for permanent damage to the engine if you ignore a faulty head gasket.

4. Replace or seal the radiator cap

The absence of a radiator cap means unstable pressure, air bubbles in the coolant, as well as a damaged radiator. This means you’d need to have a new radiator cap and have it replaced with a manufacturer-recommended one or an OEM.

Replacing it with an incompatible cap means the coolant system will have air.

5. Replace or seal the coolant reservoir hose.

A leak in the reservoir hose invites unwanted guests to the coolant and sends off the rightful occupants of the coolant. So it’s advised to have the hose replaced as quickly as possible. So aids the entrance of air into the coolant tank; coolants also find a way of escape through the leaking hose.

6. Replace heater control valve and hose

Air slipping into the coolant isn’t the only thing to worry about, the comfort and well-being of your passenger are also threatened. As such, the hose should be tightened, and the heater valve replaced if necessary. And should the hose be worn out, do not hesitate to get it changed.

7. Change the bad water pump

A vehicle’s water pump is meant to be closed at all times. But in a situation whereby the cap goes bad, it allows air into the pump inlet, so it’s best to replace the cap when it goes bad.

8. Flush coolant reservoir and radiator

The steady use of coolant creates a build-up of grime, dirt, particles, and sludge that blocks the radiator, preventing other components from working as they should. So make sure the radiator or the coolant reservoir is filled with a new coolant empty.

Frequently Asked Questions – Bubbles In Coolant Reservoir

Why Is My Coolant Bubbling But Not Overheating?

It’s normal for tanks to flow over with bubbles without it overheating. Note a boiling coolant does not mean low coolant. Preventing your engine from overheating doesn’t mean the coolant will stop functioning.

Is It Normal For Coolant To Bubble After Shutdown?

As a result of bubbling, coolant experiences air pressure. And this is all thanks to a head gasket that is blown. Low compression reduces the efficiency of the engine. Also, the cylinder’s seal is broken, resulting in a leak. Such issues shouldn’t be taken likely, and you should immediately visit the mechanic for a check.

What happens if air bubbles in the coolant system?

Air bubbles in the cooling system are one problem that shouldn’t be overlooked; it causes hot spots in the engine, resulting in overheating that could seriously affect every other engine part. To prevent this, get your engine checked at least, yearly.

How long does it take to get the air out of the coolant system?

Ordinarily, it takes at least 15 – 30 minutes for repair. But this is a determinant of the method taken and the model involved. Nonetheless, not takes about 15 to 20 minutes for the coolant to be gotten rid of and for the engine to get heated up.

How long does it take to burp the cooling system?

Patience and time are required to burp a vehicle’s cooling system. Based on the quantity of air trapped in your cooling system and the car’s model and make, the burping exercise should take about 30 minutes – 1 hour. Nonetheless, for your engine to reach medium operating temperature, it takes up to 5 – 10 minutes.

What happens if you don’t bleed air out of the cooling system?

Not bleeding the vehicle’s radiator only means you wish for the problem to persist. This problem could metamorphose into a general overheating, preventing temperatures from reaching their desired level even when increased to the highest.

How do I know if I have air trapped in my cooling system?

Symptoms of radiator airlocks are: Overheating while driving normally. Reduced performance. Malfunctioning of the heater.

Is a Bleeding cooling system necessary?

The air needs to be bled out of your vehicle’s cooling system. Hot spots or air pockets aren’t safe.  Asides from allowing the passage of heat out of the heater, it could also result in the overheating of the engine.

What can cause bubbles in the radiator?

It simply indicates the rising of air pressure inside your cooling system. Meaning the passage of liquid has been restricted by pocket air. A busted head gasket is responsible for such; that’s where the air pressure from the cylinder heads is transferred to your cooling system.

Final Thoughts

The bubbles in the coolant could mean something not minor or something minor. The boiling could occur even after turning off your vehicle. Why? Because after your cooling system goes off, the engine will remain hot. Even after the coolant has been flushed, air can remain trapped.

But parts of a cooling system or even a faulty engine can allow air inside your cooling system.

Check the radiator cap, head gasket, or other components by yourself or with the help of a mechanic. And fix whatever is causing the bubbles in your vehicle’s reservoir, so it doesn’t cause further engine damage.

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