How to Backflush a Vehicle's Coolant System

coolant system in the car engine
  • 1.5
  • Beginner
What You'll Need
Backflush kit (this can be purchased at an auto parts store)
Utility Knife
Garden Hose
Cold Water
Plastic Containers

Backflushing your car’s coolant system is an important step when servicing your car’s coolant system. It is used to completely remove any coolant that remains after the radiator is drained. It is a relatively easy process, which can be completed at home to help save on costly repair bills.

Step 1 - Find Good Lighting

Find a well-lit area to work with enough room to move around. Make sure the area is close enough for your garden hose to reach. Gather all materials together so you have them close by and readily accessible.

Make sure the car engine is cool and that it has not been recently driven. Depressurize your coolant system by removing the radiator cap.

Step 2 - Cut the Heater Inlet Hose

Cut the heater inlet hose using your utility knife. It is best to cut it at the point where the tube is the straightest. The inlet hose is the hose running from the heater core on the firewall to the top of the engine.

Place hose clamps provided in the backflush kit on to each of the cut sides of the heater inlet hose. Each backflush kit contains various sized T-tubes to fit various makes and models. Locate the correct size and fit it into each side of the cut inlet hose. Use the screwdriver to tighten the hose clamps, which will secure the T-tube to the heater inlet hose.

Step 3 - Install the Coupler and Splash Tube

Screw the black end of the backflow prevention coupler into the T-tube, then screw one end of the garden hose on to the yellow end of the coupler. Route the garden hose away from any moving parts, such as belts. The other end of the garden hose should be hooked to a faucet.

Install the splash tube from the backflush kit into the field neck of the radiator. A plastic tube can be attached to the end of the splash tube to provide better control of water flow. Position a plastic bucket under the tube to collect the fluid.

Step 4 - Drain the Radiator

Open the drain plug located at the bottom of the radiator. Use a plastic bucket to collect the fluid.

Turn on the garden hose and check to make sure water is pouring out of the splash tube. Turn on the car engine and set the heater to the highest and hottest setting. Let your car idle while water continues to run through the system. You will know the flush is complete once the water running through appears clean. This process usually takes 5 to 10 minutes.

Step 5 - Remove Flushing System

Once the water is clean, turn off the car, remove the splash tube, garden hose, and backflow prevention coupler from the T-tube. Allow the water to completely drain from the cooling system. Once all water is drained close the radiator plug and seal the T-tube with the cap supplied in the backflush kit.