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How to Change Anti Freeze Coolant in Your Cars Engine

Updated on November 6, 2011

How to Flush Your Cooling System

This article contains tips and advise on changing your own anti freeze.

Disclaimer: I am NOT a licensed mechanic, but I have a lot of "hands on" experience working on my own cars over the years.

This article contains:

  • Written Description and Tips on changing Automotive Coolant
  • List of Tools and Chemicals Needed
  • 10 Step by Step Videos showing Coolant Change Proceedure

Anti Freeze Flush n Fill Kit

Changing Your Anti Freeze Engine Coolant Step by Step

  1. Drive to Auto Repair Center
  2. Open Wallet Remove Credit Card
  3. Hand Card to Counter Clerk

… okay that is the easy way now for those of you who want to do it yourself.

You can do the entire job yourself safely and efficiently including purchasing all the chemicals and supplies for about 1/3rd to 1/2 the cost of a full system flush at a qualified automobile shop. I say qualified automobile shop because many quick lube places do not actually do a complete anti freeze flush. It depends on the equipment they use and the skill of the operator.

I recently flushed the Coolant from one of my vehicles and it was a very tiring and unpleasant experience. You would think changing the Antifreeze in your car engine would be as simple as changing the motor oil, but you would be wrong. And none of us like to be wrong… right? But I managed to get it done. Why would I change the antifreeze coolant myself? Because I’m a cheapskate? Well not really, more so because I wanted it “Done Right”. I wanted to make sure that the coolant wasn’t just changed… I wanted to be sure the system was completely flushed. I also wanted to see how much sediment and discoloration there was in the existing coolant to get a gauge as to any possible damage. If coolant is badly discolored and full of sediment it can be an indicator of war or potential wear or damage in your cooling system. Proper coolant and cooling not only assures your engine doesn’t over heat it actually protects the head gaskets, water pump, and other parts from being damaged.

Before I undertook this engine coolant changing project I decided to read up on it online and watched several videos on Youtube. There is a lot of VERY BAD information online. Even companies like Peak and Prestone have bad information online. Both of them give examples of changing your antifreeze without flushing the block. They only want to sell their product and will say whatever they need to do just that. You can NOT change your coolant in the vast majority of automobiles by simply draining the radiator. Why? Because your automobile has a thermostat that prevents coolant circulation until the engine reaches temperature. Most are set around 180 degrees. When this temperature is reached the coolant is released from the block and flows through the radiator to become cool. This is how the system works. So if all you do is drain your radiator (about 40%) of the coolant in most cars or trucks you are not draining the entire system. When you turn the motor on you have to get the thermostat to open releasing the existing coolant into the system. What happens is you end up mixing 40% new coolant with 60% old worn out coolant.

So you MUST FLUSH the entire cooling system and engine block to completely remove the old antifreeze and replace it with new antifreeze.

If you take your car into a Quick Lube type of place they may or may not flush the entire system. Some will have equipment to pull out the old coolant and replace it with new. Some will do a complete chemical flush and refill. It’s up to you to find out what you are actually purchasing. If you are paying $24,95 you are likely not getting a full flush.

How to Drain and Replace your Automobile Anti Freeze at Home

First you should know there are two types of Anti Freeze Coolant Base – Propylene and Ethylene Glycol. Propylene is the “safe” kind and is actually an additive used in some food products, Ethylene is toxic and especially dangerous to animals and pets because it has a color and as I understand it a taste that attracts them and can kill them. It can kill people too of course so don’t drink it – obviously.

What You’ll Need to Change/Flush your Anti Freeze

  • Safety Glasses – Protect your eyes!
  • Nitrile Gloves
  • Back Flush Kit
  • Coolant System Flushing Chemical
  • Anti Freeze Tester (Buy the one for Polypropylene if you use "Safe" Anti Freeze)
  • Catch Bin (Coolant Drain Pan)
  • Pliers, Screw Drivers, etc. to remove and replace hoses
  • Coolant – Anti Freeze
  • Distilled Water or Garden Hose and Tap Water (More on this below)
  • Containers for used coolant
  • Patience
  • Some Mechanical Skill

Note: I have used Zerex, Prestone, and Peak at different times. My preference is for the new Peak Global Extended life which is amber in color and uses Organic Acids, but for my last flush I used Prestone Extended life because there was a rebate. Make sure you know what type of coolant your engine requires. Aluminum Block Engines on many newer cars may require a special coolant as will GM Cars that use “Dexcool”. Just be sure to use the correct antifreeze for your application.

Lets begin the coolant flush process.

TIP: Before you start "Flushing"... actually before you do anything (Although it's okay to drain the radiator first) you will need to install the "T" connector in your INLET Heater Hose cooling line. There are 2 heater hoses on your car. The INLET hose is the one that connects from the Fire Wall to the TOP OF THE ENGINE... the other hose connects down to the water pump.

Because I did not want to cut my hose to insert the "T" I stopped by the Auto Parts store and purchased an additional foot of 5/8" heater hose. Hose size will vary by car, so check yours before if you plan on doing this. 5/8" is pretty standard though. Disconnect the INLET hose at the firewall and insert the "T" connector. When you are done you can take the "T" out and reconnect the heater hose. If you do it at the firewall you can hold the hose high in the air and not waste the new coolant that would drain out of the hose if you disconnected at the engine block.

Make sure you have all your tools, and your anti freeze on hand before beginning. Make sure you also know how much coolant your cars system requires.

First you must have your car high enough in the air to give access to the radiator drain and to allow you to place your catch bin beneath the drain so you do not let anti freeze run into the storm sewer. In many places there is a law that requires the antifreeze to be disposed of at a waste disposal facility. In the major metropolitan areas you can usually flush it down the toilet as waste water treatment facilities are set up to deal with Ethylene Glycol. If you raise your car up it should be level so everything drains properly. If you drive up on ramps be sure to block the other wheels. Always use jack stands and never get under a car that is only being supported by a jack. Use common sense, and always double check for safety. It’s your responsibility to know the waste disposal laws in your area. It is NEVER okay to drain anti freeze into the ground or storm sewers.

Once you have appropriate room to work underneath your car take your catch bin (I used a large Rubbermaid 10 Gallon tote) and place it under the radiator drain valve. If you can not access the drain valve you can also pull the hose out from the bottom most part of the radiator by removing the hose. If you do this make sure your hose is in good shape before you begin, otherwise you could have a damaged hose and end up needed to visit the auto parts store. If you pull the hose it’s a good idea to replace the clamps when you put the hose back on. This can be especially helpful on old hoses where clamps can corrode.

Let the anti freeze drain into your bin then refill the radiator with plain water. This is where you have to decide if you are going to use tap water or distilled water. The problem is the home flush kits use a garden hose so you can’t really use distilled water at least at this step. Because most people will not pull the drain blocks on the engine block and choose to backflush with a home kit (I used the Prestone Kit but Peak makes them as well). Once the antifreeze is drained refill the radiator and add the coolant flushing chemical. Most will recommend running the engine at operating temperature for 10 minutes. Be sure you have your heater on the highest setting while running so the heater core is flushed as well.


After the coolant flushing chemical step is completed make sure you let the engine cool back down. I can not over emphasize this point.

Once the engine is cool it’s time to drain and catch the used coolant and chemical flushing agent. You do this by draining the radiator and then using the garden hose to backflush the coolant through the entire system including the block and heater core. Flush the entire system as many times as it takes until the water runs clean.

Drain the radiator again. Then follow the instructions on the backflush kit in order to refill the system with new coolant. In most cases you can just drain the radiator and fill it entirely with new coolant and get at least a 40/60 mix of coolant to water. This is fine in warm climates. But if you need or want the 50/50 recommended mix you’ll need to follow closely the instructions on the backfill kit to push the extra 10-20% you want into the system.

The hardest part about the entire process is all the time it takes to wait for the engine to cool down. If you have aluminum block you do not want to just get everything really hot and then dump a lot of cold water into the block each time. If you are in this situation you are probably best paying a reputable shop to do the flush for you, but make sure you ask the right questions to make sure they are truly cleaning/flushing and replacing all the fluid.

I know a picture is worth a thousand words and I intended to take pictures of the process but with all the chemicals and water I simply didn’t have time to document it step by step.

Good luck. And yes I’ll be happy to answer questions in the comment section

Parts list for Changing/Flushing Anti Freeze

Below are some of the parts you may not have, but will need to change your Anti Freeze. Most of these items you can get at your local auto parts store. But if not you can always order them from Amazon.

NItrile Gloves are CHEMICAL RESISTANT therefore a better choice than Latex when working with automotive fluids.

Anti Freeze Tester for Ethylene Glycol

Videos - How to Dlush Your Engine Cooling System

"In this Clip we are going to talk about the proper way to flush your cooling system" is the first phrase on each of the Videos below... followed by an explanation of the steps. You may not need to watch all of these but it can't hurt.


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