How to flush a radiator & engine block

Updated July 19, 2017

Draining and flushing your car's radiator and engine block is an important part of preventive maintenance. Flushing the engine and radiator refers to the draining of the existing coolant, the flushing of the engine and radiator with a cleaning fluid and the filling of the cooling system with fresh coolant. Depending on who you talk to, the consensus on when you should do this maintenance task ranges from every year to every two or three years.

Park the vehicle on a flat, level surface and let the engine cool off (if the car has recently been driven). Locate the drain plug (or petcock) at the bottom of the radiator. Place a container under the plug, loosen the plug with a wrench and drain the coolant into the container. Tighten the drain plug.

Locate the coolant drain plug on the engine block. This will be located near the bottom of the engine. Remove the plug and drain the block from the engine's water jackets into a container. Reinstall the plug.

Fill the radiator with fresh, clean water and the chemical radiator cleaner you are using. Drive the car for about 15 minutes with the heater on "High." This will allow the water and cleaner to flush the heater core.

Park the car and let it cool again. Drain the radiator and block again. Run clean water through the radiator and the cooling system with a garden hose. Unplug the drain from the bottom of the radiator and from the block, so that the water can flush through the cooling system. Keep flushing until the water comes out of the drain plugs clear and free of particles.

Tighten the drain plugs. Fill the radiator with the appropriate type of coolant for your vehicle. Start the vehicle and let the engine get up to operating temperature. Check the level of the coolant to make sure it is still full.


When flushing your car's radiator and block, this is also a good time to install new radiator hoses and a new thermostat as a means of preventive maintenance.

Things You'll Need

  • Socket set and ratchet
  • Garden hose
  • Radiator chemical cleaner
  • Water
  • Fresh coolant
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About the Author

William Zane has been a freelance writer and photographer for over six years and specializes primarily in automotive-related subject matter among many other topics. He has attended the Academy of Art College in San Francisco, where he studied automotive design, and the University of New Mexico, where he studied journalism.