Flushing a Car's Radiator

A Step-by-Step Guide

Your car's radiator and cooling system need to be clean to be cool. As time goes on, your car's radiator builds solid deposits that can clog the cooling system. A quick, inexpensive radiator flush can keep the system in shape. It's important to change your antifreeze seasonally.

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Prepare for Your Car Radiator Flush

Mechanic refilling auto radiator.

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Before you start your radiator flush, make sure you have everything you need. There's nothing worse than draining your radiator only to realize that you need to drive to the auto store for something!

What You'll Need to Perform a Radiator Flush

  1. Phillips head screwdriver or wrench (whichever your radiator drain requires)
  2. Cloth rag
  3. Radiator Flush solution
  4. Coolant
  5. Funnel
  6. Used coolant receptacle

*Be sure to let your engine cool completely before you loosen or remove the radiator cap. Hot coolant can be painful!

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Drain the Radiator and Cooling System

Drain the coolant to begin the radiator flush.

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The first step in your radiator and cooling system flush is to drain the old coolant from the radiator.

Using your owner's manual or look for it yourself, locate your radiator's drain plug. It could be anywhere along the bottom of the radiator and will be either a screw plug, bolt plug, or a petcock (simple drain valve). Be sure you have your used coolant receptacle in place under the drain before you open it up.

With your coolant catcher underneath the drain, unscrew it and let the coolant empty completely. If you have a screw or bolt type radiator drain plug, remove it completely. If your radiator has a petcock, open it all the way.

*IMPORTANT: Coolant can be very dangerous to pets. It tastes sweet to them but ingesting it can be fatal. Be sure not to leave any—even a small puddle—where an animal could drink it.

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Add the Radiator Flush Cleaning Solution

Add all of the radiator flush solution.

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Once all of the coolant has drained from the radiator, replace the drain plug and remove the radiator cap. Add the contents of the radiator flush solution to the radiator, then fill it to the top with water.

Replace and tighten the radiator cap. Now start the car and let it run until it gets to its operating temperature (the place on the temp gauge that it normally stays at).

Turn your heater on and move the temperature control to the hottest position. Let the car run for ten minutes with the heater on.

Turn the car off and wait for the engine to cool off. If the radiator cap or metal radiator is hot to the touch, it's still too hot to open.

*IMPORTANT SAFETY REMINDER: Do not attempt to loosen or remove the radiator cap while the engine is hot. Your cooling system is hot!

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Drain the Radiator Flush Solution

Drain the contents of the radiator.

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Once the engine has cooled down, open the drain and completely empty the contents of the radiator. Your radiator flush need!

Depending on the size of your coolant receptacle and cooling system, you might have to empty it into a separate container to make room for the second draining. No matter what, never pour coolant on the ground.

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Refill the Radiator - Radiator Flush Complete

Most cars fill through the coolant reservoir.

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Now that you have performed a radiator and cooling system flush, all you need to do is refill the radiator with fresh coolant. Be sure to use the type of coolant that is correct for your car's cooling system. If you're unsure, consult your vehicle owner's manual to be sure. 

Replace the radiator drain plug or fully close the petcock.

Using a funnel to eliminate spills, fill the radiator with a 50/50 mixture of coolant and water. I'm a big fan of the premixed coolant that's become popular lately, it eliminates the measuring or guessing step. With the radiator filled, go ahead and fill the plastic coolant reservoir if your car has separate openings, again with a 50/50 mix.

Tighten all of your caps well and you're like Fonzarelli—cool!

It's a good idea to check your radiator coolant level in a day or so to be sure it's proper, sometimes an air bubble works its way out and you need to add a little.