How to Flush a Radiator
How to Flush a Radiator


Most people don't ever think to clean their car radiator, but if it's not properly maintained, debris and mineral buildup can accumulate and reduce the functionality of your vehicle's cooling system. This could result in engine damage.

A radiator is an important part of your car engine's cooling system, allowing water or coolant to circulate through small tubes that are cooled by incoming air. Radiator fluid, also known as coolant or antifreeze, helps to dissipate the excessive heat generated by the engine, to prevent overheating and engine failure. This liquid cycles around the hot engine, cooling off the metal parts by moving the heat into the radiator to be cooled before circulating again.

Like most fluids running through engine components, radiator fluid tends to build up unwanted contaminants over time. Eventually, this can lead to radiator corrosion, rust, and scale. A coolant flush helps with reducing this problem, but simply draining the radiator could leave some coolant and contaminants behind. This could then mix with and pollute your new antifreeze and cause overheating. Instead, a full flush is recommended, forcing the removal of all contaminants and debris before adding new fluid.

Your choice of cleaning product is important, to avoid damaging your radiator and potentially your engine. Avoid using vinegar, because the acetic acid makes metal susceptible to rust. Additionally, bleach or products containing it, should never be used, because sodium hypochlorite (bleach) will corrode metals such as steel and aluminum, damaging the vehicle's intake manifold, block, or engine head as well as degrading rubberized gaskets and seals.

Simple Green Pro HD is non-corrosive, safer for cleaning aluminum, stainless steel, and other metals. The professional-grade, engine-safe formula breaks down tough grease, oil, grime, and other automotive fluids.

Directions For How to Flush a Radiator:

Check your vehicle Owner's Manual before cleaning the radiator. Most 4-cylinder vehicles have a capacity of around one gallon. Make sure the radiator is cool to the touch before opening the radiator cap.

  1. Dilute cleaner. In a large container, mix 1 part Simple Green Pro HD to 3 parts water.
  2. Drain radiator. Place a drainage pan or other container beneath the drain cock opening on your radiator. Remove the fill cap from the top of the radiator. Use gloves or pliers to open the drain cock on the bottom of your car's radiator and drain it. Dispose of the fluid properly. Replace the drain plug.
  3. Add cleaner. Pour the cleaning mixture slowly into the fill hole on the top of the radiator. A funnel may be useful for this. Let the mixture remain in the radiator for 5 minutes.
  4. Start engine. Turn on the vehicle and run the engine for 5-15 minutes to allow cleaner to cycle through the lines. The motor needs to warm up to operating temperature to allow the thermostat to open and let coolant flow from the radiator to and around the motor and back.
  5. Drain cleaning solution. Turn off the engine. Open the drain cock and allow the cleaning mixture to drain. Then replace the drain cock. Dispose of the used cleaner properly.
  6. Rinse. Fill radiator with water (if possible, use distilled, non-mineralized water). Turn on the engine and allow it to idle for five minutes. Then turn off the engine, open the drain cock again and allow the water to drain. Replace the drain cock.
  7. Add coolant. Add the recommended amount of coolant to the radiator.


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