The Importance Of A Radiator Flush


A periodic coolant flush can do a world of good

Read in this article:

What a Car’s Coolant and Radiator do

A radiator flush is the process of flushing out the cooling system of your vehicle, discarding the old coolant to replace the vehicle's coolant with a fresh mixture. The cooling system is vital to your vehicle; but what does the radiator do? An internal combustion engine (ICE) generates a lot of heat through friction, burning fuel, and expelling hot exhaust gases. It would overheat if the excess heat were not dissipated by the car's coolant fluid through its radiator. This is true for all cars and trucks with ICEs, whether it's a diesel engine in a truck, the gas engine in a hybrid vehicle such as a Toyota Prius, or just a normal old Camry.

So, the fluid in the cooling system dissipates the heat produced by the engine - but what is the coolant or radiator fluid made up of? It's not just water in the radiator; usually, this is a blend of water and antifreeze, which keeps the liquid from freezing in cold weather and, at the same time, boiling over when hot - read all about engine antifreeze here. This fluid is circulated by the water pump and absorbs the engine's heat. It's then pumped to the radiator where it is cooled through fans and exposure to cool air and returned to the engine to keep it running at a constant temperature. Changing the radiator fluid and doing a coolant flush are needed periodically. The big questions are, why is a coolant flush necessary, and how often should it be done?

Radiator Flush BMW

Why Should I do a Coolant or Radiator Flush?

There are several good reasons for flushing the cooling system:

  • It gets rid of old antifreeze that might have lost some of its efficacy
  • Clears out abrasive particles that accelerate wear
  • Offers fresh protection to the whole cooling system
  • Removes rust from the system and protects against it
  • Lubricates and extends the life of the water pump and hoses

How Often to Flush the Coolant

How often to flush the engine's coolant system partly depends on the service life of the factory antifreeze used. Some types can last years but must be replaced eventually - typically every 50,000 to 100,000 miles. Additionally, over the years, corrosion and impurities picked up from the cooling system become suspended in the coolant and may build up and interfere with the performance of the system. Your car's owner's manual should contain information on how frequently to flush the system and what antifreeze to use. But, if you notice any of the following symptoms, you may need to consider flushing the radiator and cooling system:

  • There is debris, rust, or corrosion on your radiator
  • Engine overheating or abnormally high engine temperatures
  • Gurgling, grinding, or knocking sounds from the engine
  • Sweet smell from underneath the hood is a sign of a potential coolant leak

How to Flush a Cooling System

If you're attempting the job at home and you're not leaving it to a radiator-flushing service center, research your vehicle and study online tutorials on how to drain the radiator and how to do a cooling system and radiator flush on it. This includes the appropriate access points, what to strip, and how to fill and bleed the system.

You'll typically need these items as part of your flushing kit:

  • Distilled water
  • The correct type of antifreeze
  • A funnel
  • Safety glasses and rubber gloves
  • The correct tools, such as wrenches and screwdrivers
  • A large pan to collect the old coolant
  • Enough towels to soak up spilled coolant
  • Oil degreaser and a car-radiator or cooling-system cleaner

You'd normally go through these steps:

  • Preparation: Park the vehicle on a flat surface, let it cool down, and have the required tools listed above and the appropriate quantity of fluids ready. The system may hold as little as five quarts; however, a hard-working truck such as a Ford F-150 can hold much more, so be sure to check your owner's manual. Perform a visual inspection of the system to check for leaks, damage, or cracked pipes that might have to be attended to first.
  • Draining: Remove the radiator cap and then remove its drain plug to drain the coolant into the pan. Replace and properly tighten the drain plug once the system is empty.
  • Flushing: Using the funnel, pour the radiator cleaner into the system and top it up with distilled water. Replace the radiator cap and, with the interior heater set to maximum, run the engine for ten minutes. Let the engine cool, then drain the fluid. The darker its color, the more gunk was removed. Repeat the entire process, but with only distilled water, and keep repeating until the water is clear. This may require several flushes.
  • Refilling: Pour the appropriate amount of the correct type of antifreeze into the empty system - usually fifty percent of the coolant mixture. Top it up fully with distilled water. Run the engine for ten minutes again with the heater on full blast, then top up with distilled water. Bleed the system to purge any air from it if your model requires it.
Radiator Fluid Toyota
Car Coolent


Your car's cooling system is dependent on the correct coolant mixture to keep your car from overheating and to prevent the liquid from freezing in winter. The antifreeze also lubricates parts such as the water pump and inhibits rust. It is critical that you use the correct coolant and water mix. With the right maintenance, even old used cars should provide many trouble-free miles of driving without ever having to worry about the cooling system.


How long does a coolant flush take?

You must drain the system, flush it with radiator cleaner, and flush it repeatedly with distilled water until the water is clear - running the engine for ten minutes in between and letting it cool for 30 minutes after running the engine. Difficulty getting to the right access points will extend the process. It can easily take several hours to complete the process.

May I mix different types of antifreeze?

While the different types of antifreeze are all glycol-based, they have different additives and should never be mixed. Don't rely on the color and make sure of the exact specification of the correct antifreeze. Mixing different types may have consequences such as coagulation, which can block your cooling system. Usually, you can mix different brands, as long as they have the exact same formulation.

How do I know when to change my coolant?

Consult your owner's manual for the coolant's replacement intervals. Warning signs that an antifreeze flush is needed include overheating, despite the coolant being topped up. Your car might be overheating for several reasons though. If you see any debris in the radiator water, a flush is in order too. It's better to do it preventatively than to wait for a problem to arise. For more on preventative maintenance, read here.

What is the cost of a coolant flush?

The biggest cost is your time because it could take an entire day. Buying the fluids should not cost much and will often work out to less than $30. Costs get added if you have to replace parts or old hoses. Having a flush done at a local service center might set you back at least around $100 or so; the official dealership will be more expensive still.

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