Ask a mechanic online and get answers to your car questions

Ask an Expert, Get an Answer ASAP!

How to flush a car radiator 

Did you know that the main cause of engine-related breakdowns is cooling system failure? The good news is that you can protect your car from overheating by regularly maintaining your cooling system. One of the key components of the cooling system is the car’s radiator. The car radiator funnels and cools the liquid coolant that has been heated by the engine. Today, most car radiators are made out of aluminum, which needs to be protected from corrosion to survive. The corrosion protection in most antifreeze products only lasts approximately two years. Additionally, sludge can build up inside the radiator over time, which makes the coolant less effective and can cause poor gas mileage, as well as depleted engine performance. Therefore, it is important to perform a radiator flush every other year to ensure your radiator is working as effectively as possible.

Basic Preparations

First, you need to park your car where spilled coolant will not run into a storm drain or onto the ground. Remember that your car needs to be in a location where you can easily access it. You will also want to have room nearby for the tools and supplies you need to have within reach.

Your car’s engine must be cool before you flush the radiator, so be sure to park the car well in advance of (preferably at least two hours prior to) when you plan to do the radiator flush.

Tools and Supplies You May Need

Gather the following tools and supplies, and have them ready to use before you start the radiator flush:

  • Screwdriver Set
  • Socket and Ratchet Set (your vehicle may not require this)
  • Jack and Jack Stands (depending on your vehicle)
  • Nylon Brush
  • Drain Pan (with lid)
  • Garden Hose
  • Funnel
  • Several Empty Gallon Jugs (for mixing water with new coolant, as well as for disposing of old coolant)
  • Work Gloves
  • Old Towels or Rags
  • Bucket of Soapy Water
  • Radiator Cleaner (if desired)
  • Fresh Antifreeze
  • Distilled Water

How to Flush Your Car Radiator

Flushing a car radiator is a two-part process—first you drain, then you flush. It is important to note that you are not simply removing the old coolant and adding new.

First Steps

  • Ensure that your car engine is totally cool. This is essential. Hot coolant can cause injury to your skin.
  • If you have a jack, jack up the front of your car. This is not required, but it will give you better access to the radiator and will also eliminate air bubbles from forming in your coolant when you flush your radiator.
  • Lift the hood of your car and secure it, so it stays open.
  • Locate the radiator. It is usually next to the engine, near the front of the car. Using a nylon brush dipped in soapy water, clean the metal slats (fins) on both sides (front and back) of the radiator. These fins are designed to allow air to move through the radiator. Be sure to brush in the direction of the fins as you remove the dirt and grime. (If you brush against the fins, you could damage them.)
    • If the A/C condenser is mounted in front of the radiator in your car, you may not be able to access (and thus clean) the radiator slats.
  • Ensure your radiator is in good working order. Before you waste time and money flushing your radiator, be sure that it does not need a larger fix that requires professional help. Check for major signs of corrosion, as well as leaky hoses or pipes. Inspect the radiator cap for signs of wear. The tension between the lid’s seal and spring is what helps the radiator maintain the right pressure. If everything looks fine, you are ready to drain the radiator. If the only issue is a worn-out radiator cap, you can simply purchase a new cap and proceed with the radiator flush.

Draining Coolant

  • Determine your car’s coolant capacity. Check the coolant system specs in your car’s manual. Knowing the total capacity will help you recognize approximately how many quarts will drain out. Usually, you can only remove 40 to 50 percent of the coolant from your car by draining your radiator. So, calculate 40 percent and 50 percent of your car’s coolant capacity as guidelines. This will also help you choose the right size of drain pan, so you do not overfill it.
  • Put on work gloves—the sturdier, the better. Coolant is toxic, so you do not want to let it touch your skin. Also, have a rag handy to clean up any spills.
  • Center your drain pan under the radiator’s drain valve or petcock. A petcock is a small plug you can remove to drain fluid. You can usually find the petcock attached to the bottom of one of the radiator tanks.
  • Pull out the petcock, and drain the radiator. When you have drained approximately 40 to 50 percent of your coolant, you are ready to flush the radiator.
  • Cover the pain with a lid, so you do not spill any coolant when you move it. Carefully pour the old coolant into a sturdy empty container with a lid. You can dispose of it at your local hazardous waste disposal facility or check with a professional mechanic about disposal options.
  • Replace the petcock in the radiator.

Flushing With Water

  • Insert a garden hose into the fill spout of the radiator. Fill the radiator until you see the water line.
    • If you want to use a radiator cleaning solution, add it first before filling the remainder of the radiator with water. Follow the directions on the product you choose.
  • Screw the radiator cap back on securely.
  • Start your car, and leave it on for approximately 10 minutes with the heat on. Let your car engine cool before continuing.
  • When the radiator cap is cool enough to touch, center your empty drain pan under the radiator’s petcock.
  • Wearing work gloves, remove the petcock, and let the toxic water-coolant mixture drain out into the drain pain.
  • Carefully remove the pan and pour its contents into a disposable container with a lid. (Remember, this is hazardous waste so dispose of it properly.)
  • Repeat this flushing process two or three times.
  • Ensure all the liquids are drained before you refill the radiator with fresh coolant.
  • Wipe up any drips with a rag. Coolant is toxic to children and animals, so you want to leave the area free from drips and spills.

How to Refill Your Car Radiator

  • Determine the type and amount of coolant your car needs. Use the coolant capacity information you figured out earlier when draining your radiator. Check your car manual to find which antifreeze is best for your car. Most cars use green, but some require red. And, though orange coolant is newer and reported to have a longer lifespan, it is best practice to use the same coolant, rather than change it up. So, unless your car has always used orange coolant, stick with the green or red your car has already been using.
  • Create a 50/50 coolant solution of antifreeze and water. Ideally, car coolant is made up of 50 percent antifreeze and 50 percent distilled water. Mix the water and antifreeze in an empty jug or bucket.
  • Using a funnel, pour the coolant solution into the radiator up to the fill line.
  • Get rid of air pockets in the radiator. Allow air to escape the radiator by removing the cap. Turn your car on, and let it run for 15 minutes with the heater on. This makes more room for coolant.
  • Turn the car off and add more coolant, so the solution is up to the fill line again.
  • Remember to safely dispose of any old coolant, and leave the work area free from any spills.
Please type your question in the field below

5 verified Auto Mechanics are online now

Auto Mechanics on JustAnswer are verified through an extensive 8-step process including screening of licenses, certifications, education and/or employment. Learn more

2421 positive reviews
Ted G.

ASE Certified Technician

Vocational, Technical or Trade Scho

1861 positive reviews
George H.

ASE Certified Technician

Associate Degree

1571 positive reviews
See all Auto Mechanics