December 12, 2023

How To Flush A Radiator

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By Jefferson Bryant

Your vehicle’s cooling system is fairly low maintenance, but that doesn’t mean it is zero-maintenance. The internal surfaces of the radiator, heater core, water pump, and engine need periodic conditioning and cleaning to ensure the system is flowing properly. The best way to do this is a radiator flush. All antifreeze coolants are formulated to protect the internals of the system, but these chemicals only last so long, once they are used up, rust and corrosion can quickly take hold, clogging up your cooling system, leaving you stuck on the side of the road.

Flush intervals depend on the type of coolant your vehicle uses, the classic green coolant (IAT type) should be flushed every 30k miles or two years, whichever comes first. Most modern vehicles use OAT (Orange or Pink) or Hybrid OAT coolants (universal), which should be flushed at a minimum of every 100k miles or 5 years, however every three years is a better plan for the modern coolant. Flushing your cooling system is not just drain and refill, you need to run a bottle of coolant system flush through the entire system to help remove any contaminants and gunk, so that your engine will run clean and cool for years to come. The minerals from tap water alone can cause major clogs and damage your cooling system.

The Process

Flushing your system starts with a drain. Your coolant is not very environmentally friendly, so you need a drain pan or some empty milk jugs to catch the old coolant so it can be disposed of properly. Start by starting the engine, turning the heater on to full hot and let the engine run briefly, no more than a few minutes, and then shut it off. This should get the valve on the heater core open. You do not want the engine to get up to temperature, just run long enough to push some coolant through the heater core.

 Open the radiator cap and the overflow bottle cap. Set up the drain to flow into your catch can and open the drain petcock. The system should fully drain within about 3-4 minutes. Once drained, close the petcock and dispose of the old coolant.

Next, add the flush to the system and fill the radiator with water. Start the engine and let it come up to full operating temperature. The heater should be on in the maximum hot position to flush the heater core. Monitor the water level, you will continually add water until the system is full. Once it reaches operating temperature, you will need to add a bit more water. Let the engine run for 15 minutes at operating temp. Shut off the engine and allow it to cool for 30 minutes or more.

Once the engine is cooled off and you can safely work around it (the coolant will be hot, do not drain hot coolant, you risk severe burns), drain the system to a catch pan. Close the petcock.

The last step is refilling the system with fresh coolant (make sure you use the correct type for your vehicle). We recommend using 50/50 mix, which does not require any additional water. This ensures that the coolant is the correct ratio as well as the water is pure distilled water and not tap water which is full of minerals that are great for people, but bad for cooling systems. If you choose to mix your own coolant, make sure you only use distilled water. Make sure you purge all of the air out of the system when filling.

With the engine filled, you can close the caps and run the engine. It is a good idea to check the coolant level after the first 20-30 miles to make sure it is full. Flushing your cooling system not only helps it last longer, but also ensures that the system is the most efficient it can be.