How to flush your radiator

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Close-up of an open car radiator. Yellow-green antifreeze is visible through the hole.

Learn how to flush your radiator and enjoy uninterrupted summer driving. (Photo Credit: CC BY/Evelyn Giggles/Flickr)

Summer driving requires a clean radiator to help your car’s engine beat the heat. Deposit buildup can clog the cooling system and lead to engine overheating that leaves you dead on the highway. Understanding how to flush your radiator and replace the antifreeze before that hot summer trip will save you money and frustration.

Your radiator flush item checklist

Make sure you have everything on this list before flushing a car’s radiator:

  • Phillips head screwdriver and/or wrench (will vary by radiator)
  • Clean-up cloth
  • Radiator flush solution
  • Antifreeze coolant
  • Funnel
  • Container for used coolant

Getting started

First, make sure the car’s engine is completely cool before loosening or removing the radiator cap. If it isn’t, internal pressure buildup can cause hot coolant to spray onto skin, resulting in serious burns.

Begin by draining the cooling system. Use your owner’s manual if needed to find your radiator’s drain plug on the underside of the unit. Place a receptacle for the used coolant underneath, then open the underside port. It will either unscrew, unbolt or be some other form of simple drain valve. Allow the used coolant to drain out completely. Be sure to clean up any coolant that hits the ground; it can be fatal to animals.

Add radiator flush solution to clean out the gunk

After draining is complete, replace the underside plug or close the valve. Remove the top radiator cap, empty a container of radiator flush into the radiator, then top off the radiator tank with water. Re-secure the radiator cap, start the vehicle and turn the cabin heater up to the highest setting. Let the engine and heater run for at about 10 minutes, then shut everything off and wait for the engine to cool. A good rule of thumb is that if the cap or radiator itself feels hot, it’s too hot to open.

Drain the radiator flush, then refill with coolant

After the engine is completely cool, re-open the lower drain plug/valve, and empty the radiator into the storage receptacle. You may need a second container, depending upon the size of your car’s radiator. Let it drain, replace the drain plug, then commence with re-filling the radiator with fresh antifreeze in the proper 50/50 mixture with water. Fill the separate plastic reservoir with the same mixture, make sure all caps are replaced and tight and hit the road. After a day of driving, re-check the coolant level, and top it off if an air bubble has escaped the cooling system.

A few words on proper antifreeze disposal

If you are unable to recycle your used antifreeze, find an Environmental Protection Agency-approved facility to deal with it as hazardous waste. Some landfills are authorized to accept used antifreeze into a designated tank. Do not dump any used antifreeze with regular trash, don’t pour it into the sewer system, and don’t dump it on the ground.

Flushing your engine’s cooling system


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