How to do a car radiator coolant flush

How to do a car radiator coolant flush

Your car needs quality antifreeze to prevent it from overheating. However, it's possible for dirt and debris to build up in the cooling system over time, which requires a radiator flush to fix.

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

What is a coolant flush?

A coolant flush is the process of draining contaminated coolant from your vehicle's cooling system, flushing it with a cleaning product, then refilling with brand new coolant. The purpose of this is 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.

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 there are some tell-tale signs that indicate when it's time for your radiator to be flushed:

  • Your car's engine is running hotter than usual: If you feel that your car's engine is much hotter, it may be time to change the coolant by doing a radiator flush.
  • The coolant light is on: Your car's dashboard will usually have a light that will illuminate if you have low coolant level. When this lights up, it's important that you check your coolant levels as soon as possible to reduce any potential damage. Check your owner's manual if you aren't sure where your warning light is located.
  • A sweet maple-syrup smell from the engine: If you notice a sweet scent coming from the engine, it's possible that there is a coolant leak, which will need dealing with as soon as possible. The reason it smells like this is down to a chemical in most coolants called ethylene glycol that smells sweet when burnt.
  • 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 a number of ways:

  • It can clog 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.
  • It can create 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 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.
  • It 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).
  • It can damage your thermostat: Small pieces of metal in your coolant can be a hazard to your thermostat, too. These can become lodged in the thermostat's valve causing it to become stuck open or closed, which can be damaging to your cooling system and engine.
  • It can create problems with your water pump: Coolant can become more acidic over time and may speed up corrosion to your water pump which will slow down engine cooling. This means your vehicle will be more susceptible to overheating.

How often should you do a coolant flush?

The manufacturer's guide that comes with your car should give you recommended coolant change intervals, which will tell 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 important 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're maintaining your cooling system all year round with a car radiator flush. It's a good idea to make use of coolant temperature sensor, to keep tabs on the engine's operating temperature.

Be aware that the above is simply a guideline, though. You should keep an eye out for any potential 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 properly, as you'll need to drain all the old fluid and fully flush the radiator before you can refill it with the new coolant. In the next section, we will be giving you step-by-step instructions for how to do a coolant flush at home.

How to flush a radiator

It can be difficult knowing what the best way to flush a car radiator is, with a lot of different advice out there 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

  1. Position your drip tray: Before you start draining your coolant, you'll need to put your drip tray in place. This will need to sit directly underneath the lower right corner of your radiator where the drain valve or tap is located.
  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 you're certain that you've drained as much coolant as possible, you should then close the radiator drain valve. It can help to look at what the maximum capacity of coolant is in your car manual, as this can indicate what percent 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 recycle centre where they will be able to dispose of it properly for you. Never attempt to wash it down the sink or put it in your bin, as coolant is considered to be hazardous waste.
  3. Use the flush solution: Now you have an empty radiator, you can begin flushing your car radiator system to ensure that it is completely clean before you add fresh fluid. Apply the cooling system cleaner according to the manufacturer's instructions through the radiator or cooling system reservoir and add some clean water in with it 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 that the gauge usually rests at). You'll then need to turn the heater settings to hot for approximately 10–15 minutes.
    NB: During this part of the process, it's possible that 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.
  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.
  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. We stock both types, and would recommend our quality range from Comma, DriveTec and Prestone.

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.

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