What is the Best Way to Do a Radiator Flush?

Maybe you’ve taken your car in for some recent service and the mechanic let you know you needed a cooling system flush.  Or perhaps you noticed your vehicle was a little low on coolant and when you went to top it off you noticed some gunk floating in the overflow tank or radiator.  Or my personal favorite, you go to turn the heat on and you only get cold air even after your vehicle is well warmed up.

Cooling System FlushThese all are good indications that it may indeed by time for a radiator flush, or more accurately a cooling system flush.  If you’ve never flushed a radiator before or you don’t know how to flush a radiator, you’ve probably got some questions. Like, how did all the gunk get into your radiator? But how did all the gunk get into to your radiator, the cap has been on tight for years so there shouldn’t be any way for contamination to get in there right?  If all that gunk that clogged up your heater core didn’t come from outside your engine then it must be coming from your engine.  Is there something wrong, or is something about to break?

Why is it important to flush coolant?

Before you go pulling the engine out of your car in search of bigger problems, lets figure out why your cooling system needs to be flushed even though it is a closed system.  Antifreeze, it turns out, is more than just green water that doesn’t mind the cold weather.  The main ingredient in Antifreeze is ethylene glycol and it is the chemical that allows antifreeze to stay liquid even in extremely cold temperatures.  Also included in antifreeze is a certain mix of lubricants and corrosion inhibitors.  Usually, water and steel don’t mix well as the steel will rust quickly.  The corrosion inhibitors in the antifreeze slow this process but never stop it completely.  Also, these corrosion inhibitors have a finite life span in your cooling system and after time will start to allow more rapid corrosion to occur.

The biggest cause for increased corrosion in your vehicles cooling system is improperly mixed antifreeze.  Many off-the-shelf antifreeze options require mixing with water before they are added to your vehicle.  If you use water from your tap to mix with your antifreeze, you are adding a whole new spectrum of chemicals to your coolant, many of which can be harmful to your vehicle.  Even filtered tap water has minerals dissolved in it, especially if you have “hard” water and many areas have high levels of iron or other metals in the water.  Also Chlorine is the most common chemical found in tap water used to kill bacteria and make sure the water is safe to drink.  Chlorine is also a very strong corrosive agent and if added to your vehicle’s cooling system can greatly increase corrosion.

Steel isn’t your only concern for corrosion particles in your cooling system.  Aluminum, copper and brass also can corrode releasing particles and the rubber hoses and gasket can also deteriorate over time adding to your cooling system gunk.

How do you flush a cooling system? (a.k.a. How to flush a radiator)

Cooling System FlushSo now that you’re worried about what may be lurking in your radiator, let’s look at how to flush your cooling system.  First, go to your favorite auto parts store and pick up a bottle of BlueDevil Radiator Flush.  BlueDevil Radiator flush has a concentrated formula with powerful cleaning agents designed to remove any gunk or scale from your cooling system without damaging any of the components.  Drain the coolant from your radiator by opening the drain valve on the bottom of your radiator.  Next drain the coolant from your engine block by opening the block drain also.  Make sure to catch all of the coolant in a drain pan, and take it to your local coolant recycling facility ort auto parts store.  After draining, close both drains.  Add BlueDevil Radiator flush to your radiator, then refill the cooling system with water.  Start your vehicle and let the engine idle for 15 to 30 minutes depending on how much long it has been since your last coolant flush.  Be sure to watch your vehicle’s temperature gauge carefully during this time to ensure it does not over heat.

Drain the water and flush solution in the same way you drained the original coolant.  For heavily corroded or high mileage vehicles, consider removing the hoses from your radiator and heater core and using a spray nozzle on a hose to inject high pressure water through the heater core, engine block and radiator.  This may help dislodge any stubborn build ups and particles and rinse any remaining flush solution from your cooling system.

Coolant FlushOnce your cooling system is empty, close the drains as before.  Refill your cooling system with the manufactures recommended type and amount of coolant.  Be sure to read the instructions on the antifreeze you purchase.  Some may require mixing with water, while others may be pre-diluted.  Often times it is less expensive to purchase antifreeze that requires dilution.  If you choose to go this route, purchase 1 gallon of distilled water for every gallon of antifreeze.  Using distilled water in your cooling system will ensure you are not adding any foreign minerals or chlorine to your vehicle.

Once your system is refilled, start your vehicle and let it idle until it reaches normal operating temperature.  Watch the temperature gauge carefully to ensure your vehicle is not overheating.  Let it idle at normal temperature for about 10 minutes then shut the car off and let every cool until it is cold to the touch.  Once everything has cooled, recheck the coolant level in your radiator and overflow reservoir and fill them to the recommended level.  Now you can close your hood and drive with confidence!


Pick up BlueDevil Radiator Flush at your favorite auto parts stores like:

  • Advance Auto Parts
  • Autozone
  • Pep Boys
  • Car Quest Auto Parts
  • Bennett Auto Supply
  • O’Reilly Auto Parts
  • NAPA
  • Prime Automotive

You can also purchase it online from the manufacturer.


Pictures courtesy of: www.cherokeeforum.com, autolistinc.com and mike-thompson.com