How to Backflush a Radiator

Written by joshua smyth
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How to Backflush a Radiator
Radiators are located under the grille at the front end of a car. (radiators,wheels,& lights of classical car/vehicle image by L. Shat from

An engine's coolant system passes coolant fluid through a series of pipes to collect heat and radiate it from the radiator. Regularly maintenance keeps the system functioning properly. It also helps prevent sudden roadside breakdowns that can necessitate much more expensive repairs. Over time, the chemicals in coolant fluid wear out, and rust and grime build up in the system, potentially clogging it. You can avoid this problem by back flushing your radiator every two years or so.

Skill level:

Things you need

  • Back flush kit
  • Wrench
  • Bucket
  • Screwdriver
  • Utility knife

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  1. 1

    Wait for your car to cool down. Servicing a radiator of a warm car can be dangerous because the fluid inside will be hot. Ideally, a radiator flush should be done in the morning when the car is cool.

  2. 2

    Unscrew the radiator cap located on the top of the radiator. This will release any pressure from the system.

  3. 3

    Drain the radiator. There should be a drain plug on the bottom, accessible from underneath the car. For the plug's exact location, check the car's manual. Place a bucket underneath the plug, then remove it and let the fluid drain out. You might need a wrench to loosen the plug. Replace the plug when you are done.

  4. 4

    Cut the heater hose that runs from the radiator into the top of the engine, using a sharp utility knife. Insert the hose onto the T-shaped junction pipe that came with your radiator back flush kit. The ends of the hose on either side of the cut should slip over the top branches of the "T." You can secure the ends by using a screwdriver to tighten down the clamps that came with the kit.

  5. 5

    Screw a garden hose over the free end of the pipe "T," and connect the other end to a hose tap.

  6. 6

    Screw a diverter into the top of the radiator, where the cap was. The diverter is a small piece that comes with your back flush kit. The water being flushed through the radiator will come out the diverter. Running a piece of hose from the diverter to a bucket will help contain the mess.

  7. 7

    Start the car and turn the heater on high. Turn on the garden hose. This will get the coolant remaining in the system circulating until it is pushed out of the diverter and into the bucket.

  8. 8

    Continue flushing the system until the water coming out of the diverter turns clear. When this happens, turn off the engine and the garden hose.

  9. 9

    Drain the radiator again to remove the flush water, then reseal the drain cap and remove the diverter. Pour a fresh fill of antifreeze into the radiator through the opening where the diverter was. When the radiator is full, replace the cap. The radiator is now flushed.

Tips and warnings

  • Dispose of any unused coolant properly by taking it to an authorised recycling centre.

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