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Winterizing Your Car – How to Change Antifreeze Coolant in Vehicle By Flushing Engine

Recently, my vehicle registration renewal form came in the mail. In North Carolina you are unable to renew your vehicle registration until you have passed a safety inspection. A safety inspection costs around $30 and basically includes an inspection of the lights, horn, wiper blades, tires, emissions, windshield glass, window tint and several other items.

When you bring your vehicle to these quick lube type places, they will always find something else wrong in addition to what you initially came in for. After the inspection, the technician told me that my vehicle passed the safety inspection but I needed new wiper blades, a transmission fluid and filter change, differential fluid change, and a coolant flush. While I was aware that the time was getting close to change many of these items, I questioned the reason he believed that I needed to change my coolant. The tech said that my coolant tested almost the same as water.

In disbelief I drove to the nearest part store and purchased a Prestone coolant checker. After allowing my engine to cool off for a couple hours, I removed the radiator cap and took a sample of the Antifreeze. Sure enough, it came out almost clear and had a freezing point just below 32° F. With winter on the way I decided to move forward and take on the project. Below is an outline of the procedure to flush and fill the coolant in a 5.7L Chevy 1500 truck. The basics are the same for most other vehicles. Ensure that your car has cooled off for several hours before proceeding. Also, always wear safety goggles.

How to Back Flush and Fill Your Vehicles Engine

Tools Needed

  • Flat blade screw driver
  • Adjustable wrench
  • Adjustable pliers
  • 9/16 socket
  • 12” of extension
  • 3/8 or ½ ratchet
  • Flush and Fill kit
  • Garden hose
  • 3’ ½ hose
  • 3’ 3/8 hose
  • 4” ¾” hose
  • 2 five gallon buckets
  • 2 bottles of radiator flush
  • 2-4 gallons of antifreeze
  • Large drain pan
  • Jack
  • Jack Stands
  • Wheel Blocks
  • Safety Goggles
  • Coolant Tester

Optional Items

Raise Your Vehicle

On many vehicles you will need to raise the vehicle to gain access to the coolant drain. Start by placing the vehicle in park and setting the emergency brake. Place wheel blocks behind the rear tires to prevent the car from rolling backwards.

Next, locate the vehicle’s frame and use a floor jack to raise the frot of your car off the ground a foot or two. Place one jack stand on each side of the vehicle close to the front tires.

The petcock is typically located at the bottom of the radiator on the opposite side of the lower hose.

Drain the Radiator

Before going any further, ensure that the engine is cool and there is no pressure in the cooling system. A good way to check this is to squeeze the upper radiator hose and check for resistance. If the hose easily collapses then you are probably good to go. If there is still pressure in the system DO NOT GO ANY FURTHER. Hot Antifreeze can cause some pretty nasty burns. If you have any doubt that the engine is not cold, wait until the next morning before you get started.

After the vehicle has cooled, remove the radiator cap at the top of the radiator. Locate the radiator drain plug. This is usually located at the bottom of the radiator, opposite of the lower hose. Place a large drain pan under the front of the car. Use a pair of pliers or adjustable wrench to turn the petcock counterclockwise to open it. On some radiators there is a nipple that can be used to insert a 3/8” piece of hose. This will allow you to direct the flow of the fluid, making the job much cleaner. Adjust the catch pan underneath. When finished draining, close the petcock and pour the used antifreeze into a 5 gallon bucket.

Pour one bottle of flush per 10 quart capacity

Run Flush Fluid Through the System

With an empty radiator, add 2 bottles of radiator flush. Fill the remainder with water from your garden hose. Close the radiator cap, start the engine and turn the heat on the highest setting possible. This allows the cleaner to circulate through the heater core clean out any debris that may be present. Run the engine for about 10 minutes, turn off and allow to cool 3 hours or more.

Drain System Once Again and Refill

After the engine has cooled, remove the radiator cap and repeat the above step for draining the radiator. After all fluids have been removed, refill the system with just water and replace the cap. Run the car once again for about 10 minutes and allow to cool.

Install Flush N Fill Kit

The Flush N Fill basically consist of a T fitting that is integrated into your cooling system. The fitting should be installed on the inlet side of the heater hose going into your heater core. This is going to be the hose that runs from the engine block to the heater core, not the one running from the water pump to the heater core. In order to gain access to the heater core intlet, you may have to remove some engine components such as the air induction system. This can be achieved by loosening the clamps using a flat blade screwdriver. The fill kit recommends that you cut the line and add this fitting in. I believe that adding this fitting into your system will only give antifreeze one more option to escape. This is why I recommend that you only temporary add this to your system. Do this by using a 4” piece of ¾” hose to temporary install the fitting. Getting the hose off the heater core may be difficult. Work the hose backwards, forwards, and side to side. It also helps to inject some wd-40 in between the hose and the heater core outlet. Once you have the hose disconnected, install the T fitting in between the existing hose and the heater core..

Insert the yellow goose neck into the top of the radiator fill neck and insert a 3’ piece of ½” hose into the end of the goose neck. Place the hose into a five gallon bucket.

Screw garden hose onto fitting. Note the position of the back flow prevention tool.

Back Flush Cooling System

Open the petcock and screw a garden hose into the T fitting. You will need to install the water back flow prevention fitting in between your hose and fitting. This prevents your coolant water from entering into your home water supply. Open the water hose valve and ensure that there is water flowing into the bucket. Start your engine and watch the water flow into the bucket. When the water runs clear you can stop the process by first turning off the vehicle and then turning off the water. This will usually take about 5 minutes. Allow all the water to drain out of the radiator. In addition, you will also want to remove the plugs in the side of the engine in order to release the water that is trapped inside. These plugs can be removed with a ratchet, extension and a 5/8 six point socket. Be sure that you are wearing safety goggles when you are performing this task. Once all water ceases to flow, replace the block drain plugs and tighten the petcock.

Add antifreeze then top off with water. Use distilled water if desired.

Add Antifreeze Coolant

Check a repair manual for fluid capacity and fluid type. For my Chevy, the coolant system hold 20 quarts and GM recommends Dex Cool. I have heard Dex Cool called by many names including Dex Clog. Some say this product clogs vital cooling ports while others say that is baloney. I did not want to take any chances so I went with the good old green universal antifreeze.

It is recommended that you fill your system with 50% to 75% Antifreeze and the remainder water. A bit of simple math shows that 50% of 20 quarts is 10 quarts or 2.5 gallons. In my case I added 2.5 gallons of antifreeze and filled the remainder with water. As the system begins to get full, squeeze the upper radiator hose to release air bubbles. Some vehicles have a bleeder screw that you will have to turn in order to release trapped air in the engine. Check your maintenance and repair manual. Start the engine and continue adding antifreeze until the engine heats up, thermostat opens, and coolant starts to flow out of the top of the radiator. At this time you will want to immediately close the cap and ensure that it is securely fastened.  Also, flush out and fill the coolant reservoir with a 50/50 mix of coolant and water. Fill it to the cold line while the engine is relatively cool. Run for about 10 minutes, turn the vehicle off and allow to cool.

Check Coolant Levels and Concentration

After the engine has cooled off, open the radiator cap and inspect the fluid level. Add water as needed. Also, use a coolant tester to ensure that you have the proper mixture of antifreeze in your system. In most areas a 50/50 mix is adequate. Once everything has been verified, close the cap and take your vehicle for a test drive. Observe the temperature gauge to ensure that it is functioning properly.

Dispose of Old Antifreeze

Ensure that you properly dispose of your old antifreeze. Do not leave your old fluid laying around where a child or animal can drink it. Antifreeze has a sweet taste and is fatal if swallowed. Call your local town hall in your area for instructions on how to dispose your fluid. Many cities have dump stations where you can drop of unwanted hazardous materials. Check Earth911.com for a location near you.

Frequently Asked Questions

Can I use Green Yellow Antifreeze with Dex-Cool?

Back in the mid 90’s when Dex-Cool first emerged, mixing the Green Yellow standard antifreeze would result in a disastrous foam or sludge.  Eventually Antifreeze manufactures developed a universal formula that can be used in both Dex-cool and standard Anti-freeze vehicles. Although the two can be mixed, I would recommend flushing out all of the Dex-Cool if converting to the green antifreeze. If you choose to add antifreeze that has been sitting around your garage for years to your Dex-Cool system, ensure that it is the universal formula. Also, remember that the universal formula is fatal to animals and humans. Be sure to use proper precaution when handling this chemical.

My Car is Overheating After Changing My Coolant. What Is Wrong?

If your vehicle is overheating after you changed the coolant then you most likely have one or multiple air pockets in your cooling system. Take a close look at the goose neck going to your upper radiator hose and on the engine block for bleeder screws. Use a wrench to crack the screw while the engine is running to allow air to escape.

There is of course the possibility of an obstruction in your system or a stuck thermostat but an air pocket is most likely the culprit.

How Often Should I Change the Antifreeze Coolant in My Car?

This is a difficult question because coolant change frequency depends greatly on the type of coolant that you are using and your driving conditions. Some coolants are rated for 30k or 2 years while other coolants such as Dex-Cool claim to last 5 years or 100k miles. If you are absolutely crazy about your vehicle and have plenty of money to spend  then I would suggest changing the coolant every couple of years.

Throughout the years, I have owned several vehicles and very rarely changed the coolant. I use a standard Prestone coolant checker that can be purchased from Advance Auto Parts or Walmart and take a sample of the coolant. I first look at the color of it and check for impurities, sludge or rust. I also check to see what the coolant is rated for. A good rule of thumb is to have coolant that is rated at 30 degrees below the typical coldest point of the year in the area in which you live. Here in North Carolina it typically gets as low as 25 degrees in the winter so I prefer to have coolant that does not freeze until 5 degrees below 0.

Should I Use Distilled Water in My Radiator?

You may have heard someone tell you that you should never use tap water in your radiator and that distilled water should only be used. While distilled water is the preferred choice, you can still get away with using clean tap water. Keep in mind that if you use tap water then you will likely introduce other minerals and chemicals to your coolant system. Overtime, this may lead to problems with rust and corrosion. At $.99 per gallon, it is better to be on the safe side.

Can I Dump Antifreeze Down a Sanitary Sewer?

If you have a septic system then the answer is no. Antifreeze will leach out and contaminate your ground water. If you are on a public sewer system then contact your local water treatment facility and ask if it is acceptable to dump your used antifreeze coolant down the drain. Some areas will allow you to do this as long as you dilute it as you dump. Apparently the ingredients break down in the sewer system and are safe for some but not all treatment plants. Whatever you do, never dump antifreeze in a storm drain. It will end up traveling to your nearest stream and polluting the water.


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