After replacing a water pump, thermostat, radiator, or hose, the cooling system may need to be refilled and bled. The tricky part is that vehicles do not all use the same procedure. Some have a bleed screw, some require a vacuum-fill tool, and some need a scan-tool routine to circulate coolant through the system.
Air left in the system can interfere with coolant circulation and cause overheating, poor cabin heat, or fluctuating temperature readings. Use the service information for your exact year, make, model, and engine before opening the system or starting the engine.
Before You Bleed the Cooling System
Work only when the engine is fully cool. A hot cooling system can remain pressurized and release scalding coolant or steam if a cap or fitting is opened. Toyota owner’s manuals, for example, warn against removing the radiator cap while the engine is hot. Follow the warning labels and instructions for your vehicle.
- Park on a level, stable surface, set the parking brake, and keep children and pets away from coolant.
- Find the vehicle-specific service procedure. Check whether it calls for a bleed screw, vacuum filling, a particular heater setting, or an electric-pump or scan-tool routine.
- Use the specified coolant and mixture. Do not assume that all vehicles use the same coolant or a 50/50 mix.
- Check for leaks or damaged parts before refilling. Bleeding will not fix a leaking hose, radiator, pump, or connection.
- Keep hands, clothing, and tools away from fans and belts. Electric cooling fans can start unexpectedly.
Cooling System Bleeding Methods
The service procedure determines which method is appropriate. A manual bleed may be specified for some vehicles. Others are designed for vacuum filling, which uses a tool to draw air from the system before coolant is pulled in. Some newer vehicles also require a scan tool or an electric-pump activation routine.
Manual bleeding
If the manufacturer specifies a manual procedure, follow its order and conditions exactly. Bleed-screw locations, whether the engine should run, heater settings, and the point at which the system should be closed vary by vehicle. Do not loosen a bleed screw on a hot or running engine unless the service procedure specifically directs it and provides the required precautions.
Vacuum filling
A vacuum-fill tool can help remove air while refilling the system, but it must be suitable for the vehicle and used according to both the tool instructions and the vehicle’s service procedure. Some systems still require additional steps after vacuum filling.
If you want to use a vacuum-fill tool, the UView 550500 Airlift cooling-system refiller is available on Amazon. Check its compatibility and requirements before buying; this tool requires an air compressor. This is an affiliate link, which means we may earn a commission on qualifying purchases at no additional cost to you.
General Steps for Bleeding a Cooling System
Use these steps to organize the job, not as a substitute for the vehicle-specific procedure. If the service instructions differ from this overview, follow the service instructions.
- Let the engine cool completely. Do not remove a radiator cap, pressure cap, or hose while the system is hot or pressurized.
- Identify the correct procedure and coolant. Check the owner’s manual or service information for the exact coolant specification, fill point, bleeding method, and any special tools or scan-tool steps.
- Check the system before filling. Make sure the repair is complete, hoses and clamps are secure, and there are no visible leaks. Do not try to bleed a system that is losing coolant.
- Fill or vacuum-fill as specified. Use the designated fill point and follow the correct sequence. Open a bleed screw only if the procedure calls for it, and use the stated precautions.
- Complete any required circulation or bleed routine. Some procedures call for the engine to run; others use an electric pump, heater controls, or a scan tool. Do not rev the engine or open a hot system unless the service procedure specifically requires it.
- Let the vehicle cool before checking the level. Once the procedure is complete and the engine is fully cool, check the level at the location specified by the manufacturer and top up only as directed.
- Recheck for leaks and abnormal operation. Follow the manufacturer’s instructions for a final check. If the temperature rises above its normal range, the heater stops producing heat, a warning appears, or coolant leaks, shut the engine off safely and arrange diagnosis.
When to Stop and Get Help
Stop the procedure if the engine begins to overheat, coolant sprays or leaks, the temperature warning comes on, or you cannot identify the correct bleed point. Do not continue driving an overheating vehicle. Air in the system can cause problems, but a faulty thermostat, water pump, radiator cap, cooling fan, or other fault can cause similar symptoms. See our guides to driving with low engine coolant and coolant temperature sensor symptoms for related information.
Coolant is toxic. Clean spills promptly and keep it away from pets and children. Dispose of used coolant according to local requirements; do not pour it into a drain or onto the ground.
Frequently Asked Questions
How do I know if there is air in my cooling system?
Possible signs include gurgling sounds, inconsistent cabin heat, coolant-level changes, or a temperature gauge that behaves unusually after cooling-system work. These symptoms can also have other causes, so check for leaks and diagnose the vehicle before assuming trapped air is the problem.
Can I bleed my car’s cooling system without a special tool?
Some vehicles specify a manual bleeding procedure, while others require a vacuum-fill tool, scan tool, or electric-pump routine. Check the service procedure for your exact vehicle before starting. If the required procedure or tools are unfamiliar, have a qualified technician do the work.
Should I raise the front of the car to bleed the cooling system?
Only raise the vehicle if the manufacturer’s procedure calls for it. Raising the front is not a universal bleeding method, and a vehicle must never be supported by a jack alone. Follow the vehicle’s lifting points and use properly rated jack stands if lifting is required.
Can I open the radiator cap while the engine is warm?
No. Wait until the engine is fully cool before opening a radiator cap, pressure cap, or other pressurized cooling-system connection. Hot coolant and steam can cause severe burns.
References
Toyota owner’s manual: overheating precautions and hot cooling-system warnings. Always use the owner’s manual or service information for your specific vehicle.
