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Summary
  • Burping or bleeding the coolant system is the process of removing air pockets for an efficient system operation.
  • In some vehicles, topping up on coolant is the last step in the burping process. All there’s left to do is warm up the engine and check the opening of the thermostat to burp the air out.
  • Raising the coolant fill area as high as possible can help remove any extra air, according to experts.

Owning a car means you have a new set of responsibilities to be mindful of. Your vehicle needs to be maintained according to the manufacturer’s recommendations if you want to keep driving it for a long time.

Maintaining the coolant system’s efficient operation is key to making the most out of your daily driver. To keep it functioning, it’s essential to burp the system every now and then.

Cooling System Operation

Before we get into the basics of burping the coolant system, it’s important to understand how the cooling process works.

In a nutshell, coolant flows through the engine while picking up heat. Once it reaches the radiator, heat is dissipated to the outside air. The coolant then recirculates to repeat the process.

Coolant temperature can go as high as 15°F (8°C) as it flows through the engine. In most cases, hot coolant comes out of the thermostat housing.

An engine coolant outlet is connected to the radiator via the upper radiator hose and clamps. Air in the radiator helps lower the coolant’s temperature.

Once it cools, the coolant passes through an outlet and the lower radiator hose before reaching the inlet side of the water pump where it’s recirculated through the engine.

The Importance of Burping Your Coolant System

Burping or bleeding the coolant system is the process of removing air pockets for an efficient system operation.

Coolant bubbles exit the radiator filler neck and produce burping sounds, hence the term.

But what makes the process important, anyway?

Air pockets can affect the overall operation of the cooling system, producing less interior heat in the process.

Caution: Don’t ever open a hot cooling system under any circumstances.

When to Burp Your Coolant System

Burping the coolant system is typically done whenever the radiator or engine block has been drained of coolant.

See also  A Short Course on Fuel Systems

Refilling the system with coolant can cause air pockets to form within the engine block, radiator hoses, radiator, and heater core.

You might think that you’ve filled the entire system with coolant once you see that the radiator’s neck is filled. However, that doesn’t mean coolant has reached the engine entirely. This is when air pockets may form.

Burping Your Coolant System

Burping the coolant system is a fairly straightforward process, and it’s also a DIY-friendly task that you can do in your garage.

Some shops use special tools for this, but you don’t necessarily have to use one to get the air burped out. It’s easier on some engine platforms than others. Some Asian vehicles (like mid-2000s Nissan Pathfinders) have to be jacked up very high in the front to let the air escape white the cooling system is being filled.

If the thermostat is in the bottom radiator hose (as in a 2.2L Toyota Camry, older VW Rabbits, and some Dodge engines), air isn’t usually trapped in the cooling system anyway.

Using a Bleed Valve

If the thermostat is in the top radiator hose, air can be trapped unless the thermostat has a bleed valve in the large plate that forms the frame of the thermostat, and most thermostats are built this way today.

Look at the shop manual and you may find that the cooling system has bleeder screws to allow air to escape while filling the cooling system. But don’t open these while the engine is running, only while you’re filling the system.

, A Beginner’s Guide On How to Burp a Coolant System

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: Note that filling the cooling system isn’t like pouring water in a bucket. You need to run the engine until the thermostat is open and make sure the cooling system is full. Be careful not to get burned by percolating coolant.

If it has an electric fan, the fan should cycle on and off at least four times (don’t run the A/C during this process). If the electric fan comes on and stays on but wont’ shut off, there may be an overheating issue that needs addressing.

photo of coolant reservoir with no screw on cap
This is a coolant reservoir. This type won’t have a screw-on cap because it’s not designed to hold pressure. The coolant enters this bottle as it expands and then returns to the radiator as the engine cools, and the radiator valve opens. | Image Source: Richard McCuistian
photo of surge tank or degas tank
This is a surge tank or “degas” tank. This type will be designed to hold pressure and will have a screw-on pressure cap and is typically the fill point for the cooling system. | Image Source: Richard McCuistian

If the filler cap is on the radiator you can modify a radiator cap to make a special bleed tool that can be used to remove the air from the cooling system.

This works if you have a degas bottle rather than the surge pressure tank. make sure you know which is which.

If the filler cap is on the radiator you can modify a radiator cap to make a special bleed tool that can be used to remove the air from the cooling system.

– Richard McCuistian, ASE Certified Master Automobile Technician

Modifying the Old Radiator Cap

diagram of homemade tool for getting the air out of the system
This is a good homemade tool for getting the air out of the system because it doesn’t allow the system to build pressure, which is dangerous. | Image Source: Richard McCuistian

To modify the old radiator cap, remove everything except the large gasket right under the shell of the cap. The spring and everything else below the cap shell should be removed (see illustration).

See also  Car A/C Maintenance Tips: 8 Rules to Stay Cool This Summer

Fill the radiator all the way up to the neck, install the modified “bleed” cap, and make sure there is plenty of coolant in the plastic degas reservoir.

As the engine warms up, the modified cap will be allowed to release air from the cooling system into the surge tank and can “drink” coolant from the surge tank.

, A Beginner’s Guide On How to Burp a Coolant System

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with CarParts.com, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: Keep the surge tank filled to its “full” line and don’t let it get low on coolant.

This will only work on platforms with a radiator cap on the radiator itself. Once the coolant is cycling back and forth to the degas bottle, there should be hot coolant only in the degas bottle when you’re done.

Replace the “tool” cap with a new radiator cap.

General Instructions

Here are general steps to burping a coolant system:

Step 1: Remove the radiator cap once the engine cools down.

Note: Never remove the radiator cap while the engine is still warm. The cooling system is pressurized, which can cause hot fluid to spray up if the cap is removed.

Step 2: Insert a clean funnel into the radiator.

Step 3: Fill the radiator with coolant while following the prescribed ratio from the manufacturer. This process might take a while since the coolant level has to drop, and air bubbles pop on their own.

Note: This might be the last step in the burping process for some vehicles. All there’s left to do is warm up the engine and check the opening of the thermostat to burp the air out.

Step 4: Squeeze the upper radiator hose to remove air pockets.

Step 5: Locate and loosen the bleeder screw. Once removed, you should hear a hissing sound while the system is filling up on coolant. Tighten the screw once bubbles begin to form.

Step 6: Attach a funnel to the coolant reservoir or radiator filler neck to let the air out.

See also  A Short Course on Cooling Systems

Step 7: Run the engine with the funnel attached to the reservoir or filler neck. This will raise the coolant temperature to improve burping.

Bubbles should burp out of the coolant, which is the system’s way of evacuating air.

Step 8: Let the engine cool down once the bubbles subside. Let coolant fall into the reservoir, and plug the funnel with the remaining coolant before removing it.

Step 9: Run the engine for another 10 minutes. Monitor the coolant temperature and check if the thermostat opens up.

Switch the fan to the lowest setting to check for feedback from the blower motor.

If the needle on the temperature gauge is high, try revving the engine to help it bleed more air out of the system.

If no air is coming out of the vents, an air pocket may be getting in the way.

Step 10: Check the upper radiator hose for heat, but proceed with caution as it can be too hot.

Tech Tips for Burping the Coolant System

Professional mechanics have a couple of tricks up their sleeves when burping a coolant system. Here are some of them that might work for you as well.

Height Is Might

According to experts, raising the coolant fill area as high as possible can help remove any extra air.

Try parking on a hill, jack up the car, or park on a car ramp.

Use an Airlift System

For vehicles with a rear engine setup, air pockets can quickly form in the corners. Fortunately, an airlift system can help you resolve this issue.

An airlift system can be attached to the coolant fill area to create a vacuum.

Make sure the adapter is tight before attaching a hose to draw in compressed air. Then, connect an air line to the adapter.

Open the valve to create a vacuum. It should only take a few minutes to evacuate the air.

A Little Aspirin Won’t Hurt

Some professionals have unconventional methods to remove air pockets, one of which is using aspirin.

Manually open the thermostat with a screwdriver and drop the aspirin between the thermostat frame and the mechanical valve.

The aspirin will keep the thermostat open while letting the coolant flow wide open. The tablet will dissolve in 15 minutes, which should be enough to get rid of the air pockets.

About The Authors
Written By Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at CarParts.com

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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