How to Remove Sludge From a Radiator


You car's radiator helps cool the engine and also aids in heating the car's interior during the winter months. A sludge-filled radiator does not allow the coolant to completely travel through the entire radiator freely, which could eventually cause the car to overheat. You can flush your radiator at home and eliminate most of the sludge that is making your radiator operate inefficiently.

Things You'll Need

  • Garden hose
  • Catch pan
  • Socket set
  • Pliers
  • Screwdriver set
  • Funnel
  • Antifreeze
  • Radiator flush kit
  • 1-2 gallons of distilled water
  • Disposable gloves
  • Rags
  • Park the car in a flat location. Allow the engine to cool so that the antifreeze will not burn you when draining it.

  • Drain the radiator. Locate the drain plug on the underside of the radiator. Unscrew it with a pair of pliers and allow the contents of the radiator to drain into a bucket or catch pan. Unscrew the radiator cap on the top of the radiator to cause the antifreeze to drain quicker. Dispose of the waste coolant at your local licensed disposal facility. Do not pour this down the drain.

  • Fill the radiator with fresh water. Replace the drain plug in the bottom and the cap on the top of the radiator. Fill the coolant system with fresh water through the coolant fill tube, using a funnel.

  • Turn on the car and allow it to run until the fan turns on. The fan indicates that the car has reached warm operating temperature and this will allow the water to run through the engine block and flush any remaining antifreeze inside.

  • Drain the water from the radiator by removing the cap and drain plug.

  • Refill the cooling system with tap water and the radiator cleaning chemicals from the flush kit, as directed on the box. The caustic chemicals in the flush kit will dissolve any remaining sludge in the bottom of your radiator. Run the engine for the time specified on the flush kit (normally 10 minutes).

  • Drain the radiator. Remove the plug and cap. Drain the contents into a collection receptacle and take the chemicals to a licensed disposal facility.

  • Fill the cooling system with distilled water. This will keep any mineral deposits from building up in the engine block or radiator. Run the engine until the fan turns on and then drain it again.

  • Fill the cooling system with antifreeze. Create a mixture of 50% water and 50% antifreeze. Fill the system with coolant and check for any leaks. Your radiator should now be free from sludge.

Tips & Warnings

  • Do not allow any children or pets to get near the antifreeze. Make sure to clean up all spills. Antifreeze is sweet-tasting to animals, but is very poisonous.
  • Wear gloves and eye protection when using the caustic flush chemicals.

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  • Photo Credit radiator humor image by John Sfondilias from
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