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How to Flush a Radiator

Pouring radiator flush into the overflow tank.

With proper maintenance and cleaning, many cars can drive well past 100,000 miles, and a venerable few can go over a million miles. Keeping your vehicle clean is one of the best ways to help it last a long time, but some parts that need cleaning may escape a car owners’ attention because they’re not within constant view. Keeping the engine bay clean is easy, for instance, but what about the inside of the cooling system? Here you’ll learn how to flush a radiator to keep the inside of your cooling system clean and working at peak performance.

Why Flush the Cooling System?

The engine cooling system moves excess heat from the engine to the atmosphere. The water pump circulates hot coolant from the engine to the radiator and heater core, releasing extra heat. Slightly cooler coolant recirculates to the engine. The beauty of such a simple system is that it lasts a long time — so long that most people forget about it.

After racking up miles, repeated heating and cooling cycles start to affect engine coolant and the cooling system. Eventually, lubricants and anti-corrosives evaporate, changing coolant chemistry. Corrosion can also flake off and float around the system. Worn coolant can lead to larger issues in your vehicle, including accelerated corrosion, leaks, engine overheating, reduced fuel economy, performance issues and even electrical problems.

How fast coolant breaks down can vary, depending mostly on coolant type and the age of the vehicle. Older vehicles usually require new coolant every couple of years, but many modern vehicles specify that they can go up to ten years before the first radiator flush and coolant replacement are needed.

How to Flush a Radiator in Four Steps

When draining old coolant, save it for recycling.Exactly how to flush a radiator depends on the make and model of the vehicle. The vehicle’s repair manual can be a real time saver. Still, the same four basic steps apply to all vehicles:

  1. Drain old coolant. On a cool engine, remove the pressure cap and open the radiator drain. Then, open any drains on the engine block. Now is a good time to remove the old thermostat as well. Install the thermostat housing temporarily, but not the new thermostat. Also, bear in mind that some thermostats are not installed separately. Since coolant is toxic, you’ll want to save the old coolant for proper recycling.
  2. Clean the system. Refill the cooling system with water and radiator flush. Start the engine and allow it to idle for 10 to 30 minutes with the heating system on high heat, in case yours has a water valve. Shut the engine off if the temperature climbs past operating temperature.
  3. Drain the cleaner. Allow the engine to cool a bit. Drain the system, saving everything for recycling. If you opted to remove the thermostat, install the new thermostat and seal the thermostat housing.
  4. Refill the system. Using premixed coolant or coolant diluted 50/50 with distilled water, refill the cooling system. You may need to follow a specific procedure to eliminate air pockets to prevent overheating. Idle the engine for 15-30 minutes and rev it occasionally to force bubbles out of the system. Once the engine reaches operating temperature, with the thermostat open and showing similar radiator inlet and outlet temperatures, install the pressure cap and fill the reservoir.

Have you looked at your coolant lately? If not, it’s worth a few minutes of your time to do a quick engine coolant inspection and consider whether a radiator flush is needed. After all, replacing coolant is significantly easier than replacing an engine.

Check out all the radiator products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to flush a radiator, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Wikimedia Commons.


Benjamin Jerew View All

Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.

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