How Often Should I Flush My Radiator? | Holts (2023)

Of all the parts beneath the bonnet, the radiator is arguably the most commonly overlooked component. It does an important job, cooling the engine and maintaining the right operating temperature whilst protecting it from freezing in winter.

Given its importance, your car’s radiator requires regular maintenance to make sure it’s working as it should. One servicing task that you can do on your driveway is to flush the radiator to remove sludge and scale, and corrosion deposits that could prevent it from protecting the engine and lead to costly leaks.

In a hurry? Take a look at our quick guide:

(Video) Tip of The Week: When to Change Coolant

  • How to flush your car’s radiator – DIY guide:

    1. Put the Drip Tray or Catch Container in place

    2. Remove the Radiator Cap and open the Drain Valve

    3. Apply the Flush Product

    4. Add Fresh Coolant/Antifreeze

  • How to tell when your radiator needs flushing
  • The benefits of flushing your radiator

How Often Should I Flush My Radiator? | Holts (1)

How to Flush Your Car’s Radiator Step-by-Step

Here’s a visual guide to flushing your car’s radiator. Of course, you can take your car to a professional garage and they’ll be happy to do it for you, but if you fancy having a go yourself and saving some money it’s fairly straightforward:

What You’ll Need

  • Clean water, preferably de-ionised.
  • New coolant/antifreeze – make sure you have more than enough and consult your owner’s manual for the fill volume of your cooling system. Coolant is available as pre-diluted ‘ready to use’ or concentrated formats. (Our recommendation would be to use Prestone for peace of mind as it can be used in any vehicle and last for 10 years or 150,000 miles.)
  • Radiator Flush product: Holts Speedflush is a fast acting cooling system cleaner which removes sludge, scale deposits & corrosion to prevent blockages and overheating.
  • Drip tray or catch container
  • Basic hand tools (pliers, screwdrivers, spanners, etc.)


  • 1. Put the drip tray or catch container in place

How Often Should I Flush My Radiator? | Holts (2)

You’ll need to slide your drip tray underneath the radiator, right under the petcock valve where the old coolant/antifreeze will drain. Make sure your catch container is big enough; the standard cooling system contains around 10 litres of coolant/antifreeze. Consult the manual if you’re unsure.

(Video) How Often Should I Flush My Radiator

  • 2. Remove the Radiator Cap and Open the drain valve

How Often Should I Flush My Radiator? | Holts (3)

Carefully remove the radiator cap (make sure it’s cool first) before unscrewing the drain valve on the bottom of the radiator. Liquid should start to flow out, so make sure your drip tray is in the right place to avoid spillage. Label the container of waste coolant appropriately and take it to the local recycle centre for safe disposal. Never let coolant drain to the sewer and keep away from children and pets.

TIP: If your radiator doesn’t have a drain valve or it’s difficult to reach, you can detach the bottom radiator hose instead. Just loosen or remove the clip holding it in place, use a thin flat-blade screw driver to loosen the hose and twist slightly to detach.

  • 3. Apply the Flush Product

How Often Should I Flush My Radiator? | Holts (4)

Close the radiator drain valve or re-attach the bottom hose. To make sure the cooling system is completely clean before adding fresh coolant/antifreeze, use a chemical flush product.

(Video) How to Quick Flush Your Cars Cooling System

Add the flush product according to the instructions through the cooling system reservoir or radiator. Top up with clean water, preferably de-ionised and then run the engine with the dashboard heater control on HOT for around 10 minutes.

TIP: Keep an eye on the water level during this time as there can be air trapped in the system. Switch off the engine if the water level drops below the minimum level in the reservoir. Wait until cool, top up with water as necessary and repeat the step to warm the engine and allow the chemical flush to do its work. Wait for the engine to cool and drain the system as described above. If you’re using the 2 part flush product, follow the instructions to drain and fill the system and run the engine again. If you’re using the one step flush product, fill the system with clean water and repeat the step above, running the engine for around 10 mins.

  • 4. Add Fresh Coolant/Antifreeze

How Often Should I Flush My Radiator? | Holts (5)

Once you’ve flushed the radiator and closed the drain valve (or reattached the bottom hose), it’s time to add the fresh coolant/antifreeze. Always use a high-quality product that will protect your car for a long time – up to 10 years is preferable.

Add the coolant/antifreeze through the radiator cap or cooling system reservoir (expansion tank). Fill to the MAX line on the reservoir and run the engine with the dashboard heater control on COLD. The coolant level may drop slightly as trapped air in the system finds its way out. There may be air bleed plugs in the cooling system – check the manual or handbook and follow the instructions to bleed the system. Monitor the system for a couple of days just to see if the level drops and add more coolant/antifreeze as necessary.

(Video) AutoZone How-To: Flushing and Filling Your Cooling System

How to Tell When Your Radiator Needs Flushing

The first place to look is the car’s manual. This provides a list of service tasks and a schedule, as recommended by the manufacturer. It tells you what to do and when, including when to change the coolant. Our recommendation is to flush the radiator at every coolant change.

If you don’t have the manual, we’d recommend flushing the radiator every 30,000 miles, or 2 years depending on which comes first. This is more important for older vehicles, especially those without a full service history. This will extend the life of the radiator and the entire cooling system.

There are some tell-tale signs that the radiator is ready for a change of coolant and a good flush. If for instance the coolant/antifreeze in the reservoir looks murky, dark or has a brownish colour, it’s time to replace it. You can also go to a garage to have the acidity of the coolant/antifreeze tested – if it’s acidic, you should consider flushing the radiator and topping up with fresh coolant/antifreeze. Easy to use home coolant testers are also available, like these ones.

What are the Benefits of Flushing the Radiator?

Keep on top of the radiator’s flushing service schedule, and you’ll effectively extend the life of your car’s engine. Over time, the coolant/antifreeze circulating in the radiator and cooling system wears out so it doesn’t protect as well as it did. This can result in deposits forming which block the system leading to overheating symptoms, leaks and engine failure.

At Holts, we’re committed to solving your car maintenance problems. To find out more, and view our complete product range, visit the homepage.



How often do you need to flush your radiator? ›

As a general rule of thumb, you should get a coolant flush every 30,000 miles or three to five years, whichever comes first. Your car's owner's manual should also outline a more specific interval depending on the manufacturer.

How do I know if I need a radiator coolant flush? ›

Here are five signs that you need this car service.
  • What Is a Radiator Fluid Flush? ...
  • 1: High Engine Temperature Gauge. ...
  • 2: Engine Overheating. ...
  • 3: Your Car Smells like Maple Syrup. ...
  • 4: White Engine Vapor or Orange/Green Fluid Leaks. ...
  • 5: Routine Maintenance Mileage. ...
  • Local Radiator Fluid Flushes at Chapel Hill Tire.

Should you run the engine to completely flush coolant out? ›

To flush with water and remove any leftover residue from the old coolant/antifreeze, top up the radiator with clean water using a hose, and replace the radiator cap. Then, start the engine and leave it running for 15 minutes.

What is the difference between a coolant flush and a radiator flush? ›

A coolant flush is another name for radiator flush, a procedure to clean your vehicle's cooling system of sediment and rust. The coolant keeps your engine from overheating while running, and from freezing in cold weather when it's not running.

Does radiator flush clean heater core? ›

After they will drain the system once more. Then they will wash out the area near the water pump, where there are a lot of little seals that, if cracked, can cause leaks and add even more debris to your cooling system. After another drain, your mechanic will wash out the heater core.

Can flushing a radiator cause problems? ›

No, a radiator flush won't cause problems if it is done correctly and flushes everything out as it is intended, then your car will run the same or better.

Will a car run better after a coolant flush? ›

A mechanic will then finish the coolant flush by adding fresh antifreeze to your engine along with a conditioner that will keep it protected for longer. This process improves the health and protection of your vehicle, so you will likely notice an immediate boost in engine cooling and performance following this service.

How effective is radiator flush? ›

Flushing your radiator is strongly recommended for the following reasons: It removes scale deposits and rust. Scale deposits and rust build up in a radiator over time. Flushing helps to take out these deposits, which get washed out with the antifreeze.

How do I flush my entire coolant system? ›

Flush the Radiator

Remove the radiator cap and pour distilled water into the radiator until full. Replace the cap, then start up the vehicle and let it run for 10 to 15 minutes. This will work the distilled water into the engine, flushing out any loose debris or corrosion along with the last of the old antifreeze.

Can I use vinegar to flush my radiator? ›

To avoid damaging your radiator and potentially your engine, your choice of cleaning product is important. Avoid using vinegar, because the acetic acid makes metal susceptible to rust. Additionally, bleach should never be used, because sodium hypochlorite (bleach) will corrode metals such as steel and aluminum.

What is the cost to flush a radiator? ›

The typical coolant exchange or coolant flush cost (or, some like to say, “radiator flush cost”) is approximately $99.99, and usually includes a full diagnosis of your car's cooling system.

How many years does antifreeze last? ›

This deteriorated liquid can trigger severe harm to your engine by failing to control the temperature. Therefore, manufacturers suggest replacing the coolant periodically. It is recommended you change coolant after the first 210,000 km (140,000 miles) or 120 months, then every 30,000 km (20,000 miles) or 24 months.

What does brown antifreeze mean? ›

Coolant that is still doing its job to protect your engine can be any variety of colors from green to red to orange, but the key is that it will be translucent. When it's past its prime, it will become a brownish color and more opaque. If it's in really bad shape, it will be a sludgy brown.

How long can you go without a radiator flush? ›

The simplest way to avoid overheating is to service the system every two years or according to your car manual recommendations. Flushing the coolant and replacing it with fresh fluid every two years or 30,000 miles is a good rule.

How long should you run a radiator flush? ›

Turn on the vehicle and run the engine for 5-15 minutes to allow cleaner to cycle through the lines. The motor needs to warm up to operating temperature to allow the thermostat to open and let coolant flow from the radiator to and around the motor and back.

Does radiator flush damage water pump? ›

Flushing after the new water pump is installed can lead to premature failure. After all, particles may get caught in the seals during the flushing procedure.

Will a radiator flush fix a thermostat? ›

Doing a radiator flush does not require any other component to be replaced. However, if the system has a lot of debris and scale in it, the thermostat may need to be replaced if it gets clogged or corroded.

Can draining the coolant without a flush cause problems? ›

Neglecting coolant flushes can lead to some serious issues: 1.) Scale and rust particles will build up in the cooling system over time. If you go too long without flushing your coolant, these particles can clog passages, potentially damaging your heater core or overheating your engine.

Does Jiffy Lube flush radiators? ›

Ensure your cooling system performs for years to come by getting an expert radiator flush and engine coolant change at Jiffy Lube®.

Is distilled water good for radiator flush? ›

Many people have “heard” that distilled water is the best water to use in a cooling system. This is wrong! While it is certainly true that distilled water's purity prevents electrolysis and scale/deposit formation, it unfortunately comes with a potentially very damaging side effect.

Is it OK to flush radiator with hose? ›

Simply connect your garden hose at one end of the radiator, tipping one end to allow the clean water to flow through easily whilst draining out at the other end. You should notice sludge or debris being expelled from the opposite inlet, continue this process until the water runs clear.

How do I know if my water pump is circulating? ›

With the engine off, open your hood and locate the water pump pulley. With gloves on, grab it and wiggle it back and forth. There should be no movement, if there is, this along with the noise is a good indication you may have a water pump problem.

How do plumbers flush radiators? ›

If you need a power flush, the engineer will connect a machine to your system. This will push a powerful, low pressure flow of liquid through your system. This dislodges sludge and rust, removing it from your radiators and boiler. It can take several hours to flush out your radiator system.

What happens if you overfill coolant? ›

Most of the time, excess coolant is expelled from an overflow hose. You'll likely see a puddle of coolant beneath your car if this has happened. In worst case scenarios, overfilling your antifreeze tank can lead to electrical damage if overflow comes into contact with engine wiring.

Can I use baking soda to flush my radiator? ›

Mix baking soda with water. You'll want approximately 5 teaspoons of baking soda per 1 litre of water. Add the solution to your cooling system and run the engine until it's hot. Drain the system before flushing it again with distilled water.

Can I use coke to flush my radiator? ›

It sounds crazy, but Coca-Cola works great for cleaning radiators. One or two fills with the coke (let it sit for 2-4 minutes) and rinse thoroughly with distilled water. The acidity of the coke removes the gunk in the radiator as well as a fair amount of loose rust.

What liquid is used to clean radiators? ›

The most preferred composition as a radiator cleaning material includes approximately 48% by weight distilled water, 2% by weight of butyl ethylene glycol base, and 25% by weight of the hydrochloric acid-based composition as described above that has a pH of less than about 1.0.

What happens if you don't flush coolant? ›

Scale and rust particles will build up in the cooling system over time. If you go too long without flushing your coolant, these particles can clog passages, potentially damaging your heater core or overheating your engine.

How much should a radiator flush cost? ›

How much is a radiator flush? The price for a radiator flush, in which a certified technician drains all the fluid out of your radiator and replaces it with fresh fluid can average between $131 and $209.

Is a radiator flush expensive? ›

The typical coolant exchange or coolant flush cost (or, some like to say, “radiator flush cost”) is approximately $99.99, and usually includes a full diagnosis of your car's cooling system.

How much should a coolant flush cost? ›

The Average Coolant Change Cost Is $98-$123 at the Mechanic, versus $20 to DIY. This price range is based on national averages for all vehicles and does not factor in taxes, fees, or your particular make and model. Related repairs or maintenance may also be needed.

Will a radiator flush unclog? ›

To unclog the radiator, you will need to drain out the old coolant, then force water through the radiator to flush out the sediments. Refill the radiator with fresh radiator coolant fluid that contains antifreeze, and your radiator will be good to go for another few years!

Can I do a radiator flush myself? ›

Flush the Radiator

Remove the radiator cap and pour distilled water into the radiator until full. Replace the cap, then start up the vehicle and let it run for 10 to 15 minutes. This will work the distilled water into the engine, flushing out any loose debris or corrosion along with the last of the old antifreeze.

How many gallons does it take to flush a radiator? ›

Use the lever to lift your car off the ground. Put on the parking brake so your car doesn't move while you're working on it. Slide a large pan or bucket that can hold at least 2 gallons (7.6 L) underneath the radiator.


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