How to Flush Your Cooling System

How to Flush Your Cooling System | Complete Guide

Your car’s cooling system’s main job is to keep your engine from overheating. Unfortunately, dirt and mineral deposits can build up in your cooling system over time which can significantly reduce its efficiency as well as cause many other correlated problems. To prevent expensive cooling system repairs, your bet is to regularly replace the coolant inside the system. Most auto repair shops offer a cooling system maintenance package. However, if you want to save some money, you can also service your car’s cooling system yourself. To help you with that, here’s a quick guide covering everything you need to know about how to flush your cooling system as well as a couple of tips and tricks of the trade to help you save some money at the same time.

What is a Cooling System Flush?

A cooling system flush, also sometimes called a “radiator flush”, uses chemicals to clean out deposits in your radiator, water pump, and cooling passages in your engine. You can remove dirt and mineral deposits with a cooling system flush to prevent clogs and blockages. A blocked cooling system can lead to expensive repairs and even leave you stranded when your car overheats.

A professional cooling system flush done at a repair shop uses chemicals and a pump system to drain, clean, and refill your car’s cooling system in only one operation. When your car will get out of the shop, your cooling system will be free of deposits and have clean antifreeze.

However, such a service is often expensive and you may not be able to have the best deal on the coolant used to refill the system. If you are on a tight budget or if doing it yourself makes you more confident that the job is done right, you can save a lot of money by flushing the system yourself. Radiator flushes are available at your local auto parts store, and the procedure is quite simple. Unfortunately, since we can assume that you don’t have a professional cooling system flush machine at home, the process takes a little more steps. Nonetheless, the result will be pretty much the same.

Cooling system expansion tank

DIY Cooling System Flush

First Step: Cleaning the Cooling System

The most common technique to clean your car’s cooling system is to add the cooling system flush to the radiator, reinstall the radiator cap and let the car run for a specific amount of time. However, different cooling system flush products may have different procedures. Make sure to follow the instructions on the bottle.

Most cleaning chemicals work best when the coolant is at normal operating temperature. Start the car and turn your heater on high. When your heater is on, coolant will circulate through the heater core. and clean it at the same time too. Your heater core is like a tiny radiator and needs to be regularly cleaned too. Certain vehicles have the theater core installed in series with the rest of the system so if it’s obstructed, the whole system might stop circulating, leading to overheating right away.

Second Step: Draining the Cooling System

Once the cleaning product has circulated for a sufficient amount of time, you’ll need to drain the coolant completely. Most cars have a drain valve located at the bottom of the radiator. This valve allows you to safely drain the coolant into a collection device. Since coolant is harmful to the environment, you should always collect used coolant properly, store it in an empty container, and return it to a recycling center near.

The first thing to do is to unscrew or remove the drain valve to empty the radiator and collect the coolant. Removing the radiator cap will help speed up the process. Once it’s done, even though the radiator is now empty, there’s still coolant contained in the engine block. If you are lucky, some vehicles have drain valves on the engine block specifically placed to drain the coolant easily. Unfortunately, most vehicles don’t.  You’ll need to refer to your car’s repair manual to see if you’re lucky or not.

If your engine block is exempt of drain valves, unplug the upper radiator hose and remove the engine’s thermostat. The best thing to use to rinse your cooling system is distilled water. You can use regular tap water, but there is the possibility that mineral deposits may begin to form. However, using distilled water to flush a whole system might be quite complicated. The most common technique is to use a garden hose, spray water into the upper radiator hose until what comes out of the thermostat housing is clear. Then, make sure to remove all drain plugs on the engine and radiator to remove as much tap water as possible.

Third Step: Selecting and Preparing the Coolant Mixture

You will notice that the terms coolant and antifreeze are used interchangeably. They are truly one and the same. However, not all coolant is the right coolant for your car. Older cars typically use a green-colored coolant, while many newer and imported cars use an orange coolant. Some manufacturers also use a brand-specific color to easily identify if the coolant used in the vehicle is OEM. Honda, for example, uses a blue coolant while Toyota’s choice is pink.

Using the wrong coolant in your car can eventually lead to serious problems. Green coolant contains silica and other ingredients. Orange coolant contains organic acids. The wrong antifreeze can erode gaskets and seals, cause coolant leaks, and lead to premature water pump failure.

Most cars and trucks use a 50/50 mixture of coolant and water. You should always use distilled water in your radiator to prevent corrosion and mineral deposits. Furthermore, never use deionized water when flushing your cooling system, as it can cause severe damage leading to expensive repairs. Tap water contains high levels of minerals that will clog up your cooling system, making all your hard work ineffective. While rinsing the system with tap water is not that bad if removed correctly, using tap water in the coolant mixture will inevitably reduce the lifespan of the cooling system’s components.

Auto mechanic refilling a coolant system

Fourth Step: Refilling and Bleeding the Cooling System

To refill the system, start by pouring coolant into the radiator. If your car is equipped with a thermostat or any other cooling system bleeding valve, remove it. Continue filling the radiator until the coolant comes out of the bleeding valve. Close the bleeding valve, then, refill the expansion tank to the normal level. Once it’s done, you need to bleed the system to make sure it’s exempt from any air bubbles. Start the engine and leave the radiator cap off. As the engine starts to warm up, the thermostat will open, and water will be sucked into your cooling system. Remember to place the heater temperature to HOT but leave the blower fan OFF.

As the engine warms up, add coolant to the radiator as the level decreases. When the engine gets near to normal operating temperature, you will see the coolant start to rise in the tank or radiator. It’s normal for coolant to overflow the radiator at that point so leave a pan under the radiator. Let the engine run until the radiator fan starts. Once the fan turns ON, it means the system is ready to go and fully operational. Replace the radiator cap. Once the engine is cool again, and adjust the coolant level in the expansion tank. You can top it off if necessary.

During the whole process, you should always keep an eye on the temperature gauge inside the dashboard. If some air bubbles are trapped in the system, the engine might start to overheat. If it happens, turn off the engine and let it cool down. Raising the front end of the car using a jack might help push the bubbles towards the radiator. In other cases, stepping lightly on the gas pedal to increase the RPMs can also do the trick.

If you have any problem bleeding your cooling system, make sure to take a look at the proper procedure inside your car’s repair manual. It’s not uncommon for cars to have a specific procedure to completely remove all air bubbles.

Car leaking coolant

Last Step: Inspecting for Coolant Leaks

You should check the coolant level in your car regularly, particularly after a flush. If you notice a rapid loss of coolant, you likely have a leak. Sometimes, radiator flush chemicals can loosen up rust or free up stuck hoses, causing leaks. If your cooling system is leaking, you should find the problem and fix it before driving the car. An overheating engine can damage expensive components very quickly.

How Much Does a Radiator Flush Cost?

Most automotive repair shops will charge you around $100 for a radiator flush. The primary difference between a shop flushing your cooling system and doing it yourself is many shops use special tools that capture and circulate the coolant. They will charge you for about an hour of labor, plus the cost of coolant and any local regulatory fees for recycling waste coolant.

DIY Costs

When you flush the cooling system in your vehicle at home, you can save lots of money. The leading radiator flush products on the market today cost between $4 and $15. More expensive products are not always better. You easily can get a good quality radiator flush for around $8.

Distilled water is usually available at grocery stores. You can figure out how much water you will need by looking at the amount of coolant you have removed. Depending on your car model, you may need anywhere from two to five gallons of 50/50 mixture.

Typically, one bottle of concentrated coolant is enough. You can also buy premixed coolant at most auto parts stores. It is more expensive, but is easier to use and takes the guessing out of flushing your cooling system. It should take you about an hour or a little more to flush your radiator at home. Maybe two if you drink a beer at the same time.

Checking your Cooling System

A yearly radiator flush is a great way to ensure that your cooling system stays in excellent shape. Many drivers like to flush their cooling system in the spring before the summer heat. This is a good opportunity to look at other parts of your cooling system that may need to be maintained too. You can inspect hoses for signs of damage, cracks or leaks, and also ensure that the thermostat and heater control valve is working correctly. If either of them is stuck open or closed, it’s a good time to replace it while you’re at it.

Last Words

Flushing your radiator at home is easy and inexpensive. Doing the job yourself gives you pride in ownership of your vehicle, confidence that the job is done right, and saves you lots of money. The average driver can save at least $80 by doing a cooling system flush by himself. Flushing your radiator at least once a year is a good insurance against major problems that can make your car overheat when you are counting on it the most. Keeping your car’s cooling system is the best way to ensure it stay in good working condition for as long as possible… taking into account that you know how to flush your cooling system properly. When in doubt, don’t hesitate to take a peek into your car’s repair manual or ask a trustworthy auto mechanic for advice.

As they say, you’re always better safe than sorry!



About Derek F

Derek grew up in Southern California and started working on cars when he was a child. He learned from his father and grandfather how to make basic repairs and maintain cars correctly. Derek rebuilt his first engine at 15 years-old, beginning an automotive career that took him to many interesting jobs. Derek has worked as an automotive detailer, managed parts warehouses and auto parts stores, and worked as a mechanic for several years doing brake and suspension work. While pursuing a bachelor’s degree in government journalism, Derek worked for an auto museum where he started to write about cars. Today, Derek uses his expertise gained from many years of practical experience to help educate DIYers and share interesting knowledge about various types of automotive repair and service. Writing about cars helps fund his numerous classic car restoration and customization projects.

Leave a Reply

Your email address will not be published. Required fields are marked *