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How to Bleed a Car Cooling System (Step-By-Step)

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  • 9 min read

The car’s cooling system ensures the engine operates at an optimal temperature, trapped air in the cooling system can lead to problems like overheating which is why bleeding the coolant system is important to do.

In this article, we’ll explain how to bleed a car cooling system, the tools needed, and things to watch out for.

How Long It Takes to Bleed Air From the Cooling System

The time it takes to bleed air from a cars cooling system might differ based on the method employed and the system’s state.

Typically, it should take about 20-40 minutes to bleed a car’s cooling system.

Equipment Needed

To bleed your car’s cooling system, you’ll need certain tools. Below is a list of what you should have available.

  • Coolant: To refill the cooling system, you’ll require a blend of distilled water and antifreeze, commonly referred to as coolant. Ensure you use the appropriate coolant type as advised by the manufacturer for your specific car model.
  • Hydraulic Floor Jack: This is essential for safely elevating the front of the car to reach the bleed valve or radiator. Always use jack stands with a floor jack to ensure the vehicle remains safely positioned when raised.
  • Jack Stands: These are vital for securely holding your vehicle when it’s elevated. They are essential tools whenever you’re lifting your car, remember to always use high-quality ones.
  • Basic Hand Tools: To remove the radiator cap and access the bleed valve (if present on your car), you’ll require basic tools like screwdrivers, wrenches, and a ratchet set.
  • Clear Plastic Tube: This is handy for connecting to the bleed valve, allowing you to channel the coolant into a pan beneath the vehicle.
  • Funnel: Useful for pouring coolant into the system neatly, preventing spills.

Before you begin the process of bleeding the cooling system, ensure you have all these tools readily available. This preparation will enable you to carry out the task both efficiently and safely.

Also, double-check that your coolant mixture hasn’t expired and is still within its recommended usage date.

Bleeding the Cooling System With a Bleed Screw

Bleeding a car’s cooling system using a bleed screw is simple, but adhering to safety measures and following the steps sequentially is vital.

Keep in mind, the position of the bleed valve can differ based on your car’s make and model. Checking your vehicle’s owner manual or consulting a mechanic can provide guidance on the valve’s precise location.

Below is a guide showing you how to bleed the cooling system with a bleed screw.

  1. Safely jack up the front of the vehicle

    Elevate the front of the vehicle to a secure height using a hydraulic floor jack and jack stands. Ensure the car is stably positioned before moving forward.

  2. Remove the radiator cap

    Find and take off the radiator cap. While it’s typically found at the top of the radiator, its location can differ based on your car’s make and model.

  3. Attach a clear plastic tube to the bleed valve

    Connect one end of a clear plastic tube to the bleed valve and place the other end into a pan below. This setup lets you observe the coolant and any potential air bubbles. The image below shows an example of what a bleed valve can look like.bleeding air from car coolant system

  4. Turn the bleed valve 2 turns counterclockwise

    Find the bleed valve, typically found near the thermostat or atop the engine block. It might be marked or have a small arrow indicating its location. Use a wrench or socket to turn the bleed valve counterclockwise.

  5. Fill the cooling system with coolant

    Use a funnel to pour the coolant mixture into the system, ensuring it reaches the correct level.

  6. Switch on the engine (in neutral so the wheels aren’t turning)

    Turn on the engine and make sure the gearbox is set to neutral, preventing the wheels from moving.

  7. Idle the car for 20 minutes

    Let the car idle for about 20 minutes. This allows the coolant to flow throughout the system and helps release any entrapped air.

  8. Set the heaters in the car to maximum

    Switch the car’s heaters to their highest setting, this circulates the coolant through the heater core.

  9. Rev the engine to about 3000 RPM

    Rev the engine up to around 3000 RPM to assist in moving the coolant and releasing any remaining air pockets.

  10. Carefully open the air bleed valve

    Carefully open the bleed valve to let out any trapped air. You’ll see air bubbles emerging from the plastic tube.

  11. Close the bleed valve when the coolant stream is free of air bubbles

    Once you observe a consistent flow of coolant without any air bubbles in the clear tube, shut the bleed valve.

  12. Refill the coolant to the required level

    Inspect the coolant level and top it up to the required mark if needed.

  13. Test drive the vehicle

    Drive the car and keep an eye on the temperature gauge to make sure the cooling system is working fine. Always check for any potential leaks and fix them immediately.

How to Bleed a Cooling System Without a Bleed Valve

If your car’s cooling system lacks a bleed valve, you can still remove trapped air using an alternative method.

Here’s a step-by-step guide on how to bleed the cooling system when no bleed valve is present.

  1. Jack up the front of the vehicle: Use a hydraulic jack along with jack stands to elevate the front end of your car. Ensure the car is stably positioned before moving forward.
  2. Take off the radiator cap: Find the radiator cap, typically situated on the radiator’s top, and take it off. However, its position might differ based on your car’s brand and model.
  3. Pour a 50/50 mix of distilled water and antifreeze into the radiator: Using a funnel, fill the radiator up with a blend of distilled water and antifreeze. Ensure you use distilled water to avoid mineral deposits in the system.
  4. Fill the coolant reservoir: Find the coolant reservoir and top it up until it reaches the “max” indicator line.
  5. Start the engine with the radiator cap removed
  6. Turn on the heater to its highest setting: Engaging the heater on its maximum setting aids in circulating the coolant through the heater core, expelling any trapped air.
  7. Allow the engine to warm up: Let the engine run until it reaches its normal operating temperature. You can observe the coolant circulating when looking into the radiator opening, and the top radiator hose will start to feel warm.
  8. Let the coolant circulate: Give it a few minutes for the coolant to move throughout the cooling system and for any trapped air to be released. When the heater consistently blows hot air, it signifies that air is being expelled from the cooling system.
  9. Switch off the heater and engine: Before continuing, make sure to turn off both the heater and the engine, and let the engine cool down.
  10. Refill the radiator with coolant if needed: Inspect the coolant level in the radiator and top it up if required.
  11. Squeeze the top radiator hose to release trapped air: After topping up the coolant, press the upper radiator hose to let out any lingering air bubbles, then fill with more coolant if needed.
  12. Replace the radiator cap
  13. Start the engine and let it reach operating temperature
  14. Drive the vehicle and keep an eye on engine temperature: Go for a drive and watch the temperature gauge to confirm the cooling system is working as it should.
  15. Check for coolant leaks: After bleeding any air from the cooling system, check for any coolant leaks and address them promptly.
  16. Check the coolant level over the next few days

Keep in mind that this technique might not be as efficient as using a bleed valve and might not eliminate all the air trapped in the system.

If you face problems with your cooling system, seeking professional help is advisable.

Signs of an Air Pocket in the Cooling System

Air trapped in the cooling system can lead to various problems affecting your car’s engine performance and durability.

Below are some signs of air pockets in the cooling system.

  • Overheating: A clear sign of air trapped in the cooling system is the engine getting too hot. When coolant doesn’t circulate effectively, it can’t regulate the engine’s heat, leading to increased temperatures.
  • Engine Damage: Persistent overheating can result in cracking and warping of the engine block, cylinder head, liners, and other parts. Air pockets in the cooling system can lead to uneven heat distribution and pressure build-ups, heightening the risk of such damages.
  • Elevated Emissions: Air pockets in the cooling system might lead to the engine not operating at its ideal temperature, resulting in higher emissions.
  • Diminished Performance: If the cooling system has air pockets, the engine might not operate at its best temperature, leading to a drop in its performance.
  • Coolant Temperature Alert on Dashboard: If there’s an air pocket in the cooling system, certain vehicles might trigger an engine temperature warning on the dashboard.
  • Limp Mode Activation: When the engine temperature rises excessively, certain vehicles may enter limp mode. This protective measure limits engine power to avoid further damage.

Bear in mind that while these symptoms can indicate an air pocket in the cooling system, they could also arise from other problems like a malfunctioning thermostat or a defective water pump.

If you notice any of these signs, it’s crucial to have a professional inspect the cooling system. Neglecting these warnings can result in significant engine damage and expensive repair costs.

Causes of Coolant to Boil

If an air pocket forms in the cooling system, it can cause the coolant to become trapped and not circulate efficiently, potentially leading it to boil.

A malfunctioning thermostat or incorrect coolant levels can also lead to this issue.

Will a Cooling System Bleed Itself?

The cooling system won’t self-bleed air; instead, the purging process must be manually undertaken to expel the trapped air.


Maintaining your car’s engine involves crucial steps like bleeding the cooling system. The steps outlined in this article should be useful for bleeding air from the cooling system of most vehicle makes and types.

It’s essential to use high-quality tools, be vigilant for signs like overheating, and inspect for any coolant leaks.

Routine checks and care of your cooling system can avert expensive repairs and extend your vehicle’s lifespan.

  • Andy Lewin

    Andy Lewin is a senior mechanic, ASE qualified master technician, and an experienced automotive engineer.He's passionate about serving the automotive community with the highest-quality and trustworthy information on all things automotive. He loves to write about car repairs, maintenance, car modifications and tuning, faults, and much more.

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