All vehicles use a liquid or air cooling system to keep the engine running effectively. But the most common of the two is the liquid cooling system. This system relies on a close network of pipes that carries coolant to the engine.
Every once in a while, you may experience coolant reservoir bubbling after shutdown. This may cause you to worry as your initial thought would be that something is wrong with your car.
So why is the coolant bubbling but the car is not overheating?
There are different bubbles that you might see in your coolant reservoir. Below are the two types of air bubbles that you might see in your coolant;
Normal Bubbles
Automotive coolers tend to work much more efficiently without air bubbles because bubble-free coolant absorbs heat faster than coolants containing air bubbles, which is a more effective way to protect the engine from overheating.
It is normal to have bubbles in the coolant reservoir after driving. Usually, air bubbles are found in the expansion tank.
Problem Bubbles
When bubbles appear in the coolant, it could signify that the head gasket is leaking. To check for a head gasket problem, test each cylinder in your vehicle with a cylinder leak tester with the engine off.
If air bubbles appear during the test, they must be eliminated as the combustion products enter the cooling system. If left untreated, the head gasket can rupture and leave you stranded.
If you are trying to identify whether you have a leak and have a hard time at it, you should check for a sweet smell in the air. Some people say it smells like maple syrup, while others say it smells like butterscotch. If you smell this from the engine, this could indicate that Antifreeze from the coolant has leaked.
Note: Antifreeze has a sweet odor and taste, and it’s important to keep it out of the reach of animals or small children.
What causes bubbles in the coolant reservoir?
The air causes bubbles in the coolant reservoir. As a result, the vehicle’s cooling system is pressurized and uses a sealed hose system that allows coolant to flow around the engine. When air finds its way into this closed system, it forms air pockets.
The air pocket blocks the flow of liquid, which leads to a rise in temperature, causing coolant to bubble inside the reservoir. Bubbles in reservoirs could be severe, and sometimes, it could be something to not worry about. So what could be the cause of these bubbles?
Air pockets
Air pockets are trapped in the cooling system when coolant is flushed and refilled. As you drive the car and it heats up, the air pockets expand and are pushed into the coolant reservoir. The expanded air pockets contract as the engine cools down; hence, coolant is sucked from the reservoir to replace air. Thus, causing the bubbles. This is normal but can be avoided.
Solution: Allow air pockets to escape after refilling the coolant
When flushing and refilling the coolant reservoir or radiator, the air is trapped in the system. Ensure all the air is expelled. Run the engine with the radiator’s cap off for fifteen minutes after refilling to remove air pockets. This will help bleed any air in the radiator or reservoir before replacing the cover.
Faulty radiator cap
The radiator cap works as a pressure seal to keep pressure in the cooling system high while letting coolant flow into the expansion tank. Unfortunately, when this cap is faulty or replaced with a non-compatible one, it allows air into the cooling system, causing the coolant reservoir to bubble.
An easy way to know bubbling is due to a bad radiator cap is that you will see bubbles in the coolant reservoir after driving for long.
Solution: Replace or seal radiator cap
The pressure starts fluctuating with the radiator cap out and can damage the radiator or allow air into the cooling system. Here, you will need to change the radiator cap to ensure you replace it with an OEM or manufacturer-recommended cap. An incompatible radiator cap will also allow air into the cooling system.
Bad thermostat
The thermostat regulates the flow of coolant in and out of the radiator. Therefore, the coolant thermostat must open and close at a specific time. First, it should open to let out the hot coolant from the engine into the radiator to cool. Then remain close for the engine to heat coolant to start the car. A damaged thermostat will not be able to determine if the coolant boiling temperature is normal.
When the thermostat is faulty, it doesn’t open and closes at the appropriate time. And thus, it causes a bubbling effect in the coolant reservoir or radiator since there is an uncontrolled airflow.
Solution: Replace faulty thermostat
With the thermostat malfunctioning, the coolant flows inappropriately, causing the coolant to bubble. The best way to avoid this is to replace the thermostat with an OEM or compatible aftermarket one. So long the thermostat is working fine, and there won’t be bubbling.
Leaky or blown head gasket
A worn or blown head gasket is a prevalent cause of bubbles in the coolant tank. When the head gasket is bad, combustion gases from any cylinder slip into the water jacket, then send air through the cylinder head into the cooling system. An easy way to know the bubbling is due to a leaky gasket is that bubbling occurs immediately after starting the engine.
Solution: Fix a leaky head gasket
Since a leaky head gasket causes combustion gas to enter the cooling system, one needs to seal the leak. To do this, take the car to a professional mechanic to fix the leak. You can fix it at home using a leak repair fluid to save a few bucks. However, if the leak refuses to seal, the best option will be to replace the head gasket.
Head gaskets are fixed in positions where one would have to dismantle almost half of the engine to get to it, and replacing it is quite an expensive fix. So it would help if you didn’t allow the head gasket to get to this point. Additionally, failure to fix it can lead to permanent engine damage.
Faulty heater control valve or hose
The heater control keeps the passenger’s compartment hot by allowing hot coolant to enter the heater’s core. When the heater’s valve is faulty or the heater’s hose connection is loosed, the air slips into the cooling system, resulting in coolant bubbling in the reservoir.
Solution: Replace heater control valve and hose
You should replace the heater valve and tighten the hose. If the hose is worn, you will still need to change it.
Leaky coolant reservoir hose
The hose that connects the radiator to the coolant reservoir must be leak-free and tight. If the radiator hose is bad or worn, air sips into the hose and causes the Antifreeze in the reservoir to bubble.
Solution: Replace or seal coolant reservoir hose
When the reservoir hose leaks, something you don’t want enters and something you need leaves. So changing the hose quickly will be a wise thing to do. Because aside from air entering the cooling system through the leaky hose, coolant also drips from the leaky hose. So you still get to experience low coolant levels leading to engine overheating.
Faulty water pump
The water pump helps circulate Antifreeze or coolant through the radiator’s cooling tubes, where it cools and flows to the engine components through the engine paths and pipes. When the water pump is bad, air enters into the pump intake. When the trapped air reaches the radiator intake or coolant’s valve, it generates bubbling.
Solution: Change bad water pump
The water pump is supposed to remain close. But when the cap is bad, it traps air in the pump intake. So the best thing here will be to replace this cap. With the cap closed, no air is trapped inside the water pump.
Rust and contamination
Like other metal components, the radiator can rust with time. In addition, when a radiator is not flushed regularly and supplied with appropriate coolant, it gathers impurities.
Check this too: Why Is My Car Overheating When Idling?
Rust, grime, and other debris can block the radiator’s tubes and distort the smooth operation of the thermostat and water pump. In addition, excessive heat lets the coolant bubble and produces fast bubbles you see in the coolant reservoir.
Solution: Flush coolant reservoir and radiator
When coolant works to an extent, it becomes dirty, forming sludge, grime, and other particles. This causes the radiator to get clogged, not allowing other connected components to function well. So ensure you regularly flush the radiator or coolant reservoir and refill with a new coolant.