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How to do a car radiator coolant flush

How to do a car radiator coolant flush

Complete Guide on How to Flush a Car Radiator

Flushing your car's radiator is essential for clearing accumulated dirt and debris in the cooling system. During this process, replacing the antifreeze in your radiator is crucial. This is important because antifreeze plays a key role in preventing your engine from overheating. 

If you need antifreeze for your car just head to our antifreeze page and we’ll show you our large selection of coolant and antifreeze available for you.

To help you avoid a costly garage visit, we'll show you how to do a coolant flush yourself in this guide. We'll cover:

  • Is Coolant and Antifreeze the Same Thing?
  • What Is a Coolant Flush?
  • 4 Signs That Coolant Needs to Be Changed
  • What Happens if You Don't Flush Coolant?
  • How Often Should You Flush Coolant Through Your Radiator?
  • How Long Does a Coolant Flush Take?
  • How to Flush a Radiator
  • How to Perform a Coolant Flush - 5 Simple Steps
  • Flushing Coolant Know-How

Is Coolant and Antifreeze the Same Thing?

Antifreeze keeps the water in a car's cooling system from freezing. When you mix antifreeze with water, it's called coolant. It's best to use a 50:50 mix of antifreeze and coolant. Always mix antifreeze with water before using it. Coolant helps control the temperature in your engine, especially in very hot or cold conditions. Learn all about antifreeze in our ‘What is antifreeze’ knowledge hub guide.

What Is a Coolant Flush?

A coolant flush is a process of draining contaminated coolant from your vehicle's cooling system, flushing it with a cleaning product, and then refilling it with brand-new coolant. This aims to rid your engine of any old fluid, dirt, debris or rust so your cooling system functions as it should. A radiator flush – also referred to as a cooling system service or a coolant flush – is a vital procedure for maintaining a healthy engine.

4 Signs That Coolant Needs to Be Changed

It isn't always easy to tell what's going on under the bonnet of your car, but some tell-tale signs indicate when it's time for your radiator to be flushed:

Your Car's Engine Is Running Hotter Than Usual

If your car's engine is running much hotter, it may be time to change the coolant by doing a radiator flush.

Coolant Light Is On

Your car's dashboard usually has a light that will illuminate if you have a low coolant level. When this lights up, you must immediately check your coolant levels to reduce potential damage. Check your owner's manual if you need help determining where your warning light is located.

Sweet Maple-Syrup Smell From the Engine

If you notice a sweet scent coming from the engine, there may be a coolant leak, which will need to be dealt with as soon as possible. It smells like this due to a chemical in most coolants called ethylene glycol that smells sweet when burnt. You can also check out guide on how to spot and repair a radiator leak.

Your Heater Isn't Working

If you notice your heater failing to get hot, this can be one of the most obvious signs that your coolant needs changing.

What Happens if You Don't Flush Coolant?

Neglecting your car's cooling system can wreak havoc on its performance in several ways.

Clogs Your Radiator

Dirt and build-ups of old coolant can clog your radiator, causing your car's engine to overheat and your heater to blow cold air.

Creates Engine Scale

Coolant is designed to prevent corrosion in your engine, but complete protection against this isn't possible. This is because cooling products have a high water content, and your engine is made from metal. But, the longer you leave old antifreeze in your engine block, the more likely it is to create engine scale.

Can Cause Leaks

Over time, small pieces of metal from your engine will contaminate your coolant, causing damage to parts like your gasket seals and hoses. Over time this can cause leaks that will inhibit your car's performance and might mean you need to replace your radiator (although there are some other causes of leaks you should be aware of). Our handy guide lets you know how to repair a leaking radiator.

Might Damage Your Thermostat

Small pieces of metal in your coolant can also be hazardous to your thermostat. These can become lodged in the thermostat's valve, causing it to become stuck open or closed, damaging your cooling system and engine. You can find more about thermostats in our ‘thermostat guide’.

Could Create Problems With Your Water Pump

Coolant can become more acidic over time and may speed up corrosion to your water pump, slowing down engine cooling. This means your vehicle will be more susceptible to overheating.

How Often Should You Flush Coolant Through Your Radiator?

The manufacturer's guide with your car should give you recommended coolant change intervals, telling you how often to do a radiator flush for your specific model. But, in general, most mechanics will recommend a routine flush every two years or when you reach 40,000 miles, depending on which comes first.

Many people believe that looking after your car's cooling system is only essential for the summer months when there's a greater chance of your engine overheating (although there are other reasons your engine could overheat). And, while it's true that you need to pay special attention to it during the hot months, it's vital that you maintain your cooling system all year round with a car radiator flush. It's a good idea to use a coolant temperature sensor, to keep tabs on the engine's operating temperature.

Be aware that the above is simply a guideline, though. You should watch for any signs that your car may need a coolant flush sooner than this.

How Long Does a Coolant Flush Take?

A coolant flush takes around one hour to do correctly, as you'll need to drain all the old fluid and thoroughly flush the radiator before you can refill it with the new coolant. In the next section, we will give you step-by-step instructions for doing a coolant flush at home.

How to Flush a Radiator

Knowing the best way to flush a car radiator can be challenging, with lots of different advice to follow. Here, we will be sharing our recommended process:

What to Use to Flush a Car Radiator

  • Clean water
  • New coolant – consult the manufacturer's manual for the exact fill volume of your cooling system.
  • Radiator flush solution/cooling system cleaner
  • Container or drip tray to catch flushed coolant – most standard cooling systems will hold approximately 10 litres of coolant/antifreeze, but check your manual for specifics.
  • Funnel

How to Perform a Coolant Flush - 5 Simple Steps

Step 1 - Position Your Drip Tray

Before you start draining your coolant, you'll need to put your drip tray in place. This must sit directly underneath the lower right corner of your radiator, where the drain valve or tap is located.

Step 2 - Remove the Radiator Cap

Remove the radiator cap and unscrew the drain valve, which will be located towards the bottom of the radiator. When the old coolant starts to come out, you might need to readjust the position of the drip tray to avoid spillages. Once confident that you've drained as much coolant as possible, close the radiator drain valve. Look at the maximum capacity of the coolant in your car manual, as this can indicate what percentage of the coolant you've managed to flush out at this stage.

NB: You should label this container stating what it is and take it to your nearest recycling centre, where they can dispose of it correctly for you. Never attempt to wash it down the sink or put it in your bin, as coolant is considered hazardous waste.

Step 3 - Use the Flush Solution

Now that you have an empty radiator, you can begin flushing your car radiator system to ensure it is completely clean before adding fresh fluid. Apply the cooling system cleaner through the radiator or cooling system reservoir according to the manufacturer's instructions. Add some clean water until it's filled to the "max" level indicated on the reservoir. You'll then need to start the engine and let it run to its operating temperature (the temperature at which the gauge usually rests). You'll then need to turn the heater settings to hot for approximately 10–15 minutes.

NB: During this part of the process, you might see the water level drop beneath the minimum level indicated by the reservoir. In this case, you'll need to wait until the engine is cool and then top up the water and warm the engine again.

Step 4 - Drain the Flush Product and Water

After having your engine on for 10–15 minutes, turn it off and wait for the engine to cool. You'll then need to drain the radiator from the valve as described in steps 1 and 2. Once you're done, close the drain valve again.

Step 5 - Add the New Antifreeze

Refilling coolant in your car is simple: funnel antifreeze into the radiator via the radiator cap or to the maximum capacity point in the cooling system reservoir. You should then run the engine and turn the heater to cold. 

If your antifreeze levels drop during this part of the process, your car's cooling system may need bleeding to release any build-ups of air – just like a radiator in your home would. It's best to keep an eye on these levels for a couple of days after adding the new antifreeze, topping it up as necessary. 

NB: Traditionally, antifreeze was bought as a concentrated solution, but with too much concentrate causing overheating, it's now possible to get premixed solutions of 50% water and 50% antifreeze. This is known as Coolant. We stock both types and would recommend our quality range from Comma, DriveTec and Prestone.

Flushing Coolant Know-How

Failing to maintain your car's cooling system can have costly consequences, with build-ups of dirt and old antifreeze impacting your engine's healthy functioning. Take the tips from this guide to learn how to flush and refill your coolant at home to keep your engine and heating in optimal condition.

Here at GSF Car Parts, you'll find a selection of cooling and heating car parts, accessories, and tools that will help you keep your car running smoothly for longer

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