Cooling System Service: Flush and Fill

The Flush and Fill method of servicing your car's cooling system will thoroughly clean the major components of the cooling system.

These instructions should be used as only advice. Always follow your car's manufacturer's instructions when servicing it on your own.

Flushing the 'Ole Pipes
1. Start with a Cool Engine. Make sure your vehicle has not been driven for several hours before starting this maintenance job. If you need more clearance to access the under side of the radiator, jack the front of your car up and support it on jack stands or use a set of ramps.
2. Remove the Radiator Cap and set it aside. (Fig. A)
3. Locate the Radiator Drain, it will probably be on the side of the radiator opposite from the radiator cap, located towards the very bottom of the radiator. (If your car does not have a radiator drain, skip to step 6). (Fig. B, 1=Draincock, 2=Drain)
4. Attach a Hose to the radiator drain, if needed, and route it to a large container capable of holding at least 5 gallons. (Fig. C)
5. Loosen the Draincock to open the drain. Let the old coolant drain out of the radiator (this may take 10-15 minutes depending on the size of the radiator). When all the old antifreeze has drained, tighten the draincock and proceed to step 8.
6. Locate the Lower Radiator Hose. This will be a large hose coming out of the bottom of the radiator.
7. Remove the Lower Radiator Hose, being careful to not get antifreeze on yourself. Remove the hose by disengaging the hose clamp with a tool appropriate to the type of clamp used (pliers or screw driver). Route the hose so that it will empty into a large container. When all the antifreeze has drained, reinstall the hose.
8. Flush the Radiator by running water through the radiator cap with a garden hose. When the water emptying from the radiator drain is clear, stop flushing and allow the radiator to fully drain.
9. Flush the Heater Core by finding the heater core inlet and outlet hoses. These two hoses will pass through the firewall (the wall that separates the engine bay from the cabin) on the passenger's side of the vehicle. (Fig. F) Follow the hoses to determine which is the inlet and which is the outlet. The inlet hose will come from the engine or thermostat; the outlet will come from the water pump. Disconnect the inlet hose and insert your garden hose into it (you can use a male hose adapter if you wish but it is not required). Disconnect the outlet hose and route it so that it will drain into the your large container. (Fig. G, 1=Inlet Hose, where to insert garden hose, 2=Outlet Hose, route to drain into container - Fig. H) Flush the heater core by running water through the inlet hose until the fluid coming out of the outlet hose is clear. Switch between a steady stream of water and pulsating the water to help dislodge any possible build-up inside the heater core.
10. Backflush the Heater Core by switching which heater hose you spray your water into and which you empty into the container. Follow the same flushing method as step 9 with alternating between a steady stream of water and pulsating the water stream by repeatedly spraying full blast and then switching the hose off. If you want to very thoroughly flush the heater core, you can then repeat step 9 one more time before proceeding to the next flushing step. Once the heater core has been flushed, reattach the inlet and outlet hoses in their correct spots.

11. Flush the Coolant Reservoir by removing the reservoir hose. The end of the coolant reservoir hose will be attached to the radiator filler neck (directly under the radiator cap). Disengage the hose from the filler neck and from any clips that may secure it to the top of the radiator and route it to drain into the container. (Fig. I & J)

12. With the Reservoir Hose in Place, open the top of the reservoir and use a garden hose to flush the reservoir tank out. If there is an excess of corrosion build-up inside the tank, you can use any common household cleaners to help thoroughly flush the tank. When the reservoir is clean, reroute the hose and reattach it to the radiator filler neck.
13. Refill the Radiator by slowly adding a mix of 50/50 antifreeze/water with the help of a funnel. When the radiator is full, leave the funnel in and the radiator filler neck and then fill the coolant reservoir tank to the "Cold Fill" mark.
14. Turn Your Heat on High (Fig. D)
15. Run the Engine Until it Warms Up, as indicated by the temperature gauge or the radiator fan turning on. Let the engine run for about 10 minutes AFTER it gets to normal operating temperature. (Fig. E)
16. Top Off the radiator with your blended 50/50 antifreeze/water.

To summarize:
  1. Remove the radiator cap and drain the radiator.
  2. Flush the radiator.
  3. Disconnect the heater core inlet and outlet hoses and flush the heater core.
  4. Flush the coolant recovery reservoir.
  5. Fill the radiator with a 50/50 blend of antifreeze and distilled water.
  6. Run the engine until it gets to normal operating temperature, and then for 10 minutes longer.
  7. Top off the radiator with a 50/50 blend of antifreeze and distilled water.

End Notes
While performing this maintenance, check all the cooling system components for wear and tear. Replace any hoses that show signs of imminent failure, such as cracks, bulges, swelling, or punctures. If your cooling system is in rough shape (i.e. there is a lot of rust and corrosion build-up) you can add a step of using a chemical cleaning agent flush after you flush the radiator, heater core, and reservoir. If you choose to do so, follow the directions on the bottle.
Also, I should point out that following the steps outlined for this method will leave some old antifreeze in the engine block. You can drain the engine block as well, but I personally do not because if you drain the engine block, you must run the engine without any coolant until the thermostat opens up and the shock of going from no coolant to a sudden influx of cold coolant could damage the engine. If you want to fully flush the system, I would recommend adding an additional flush step as outlined in the Drain and Fill method.

After completing this maintenance, your vehicle's cooling system should be ready to perform at its peak for at least a couple of more years!

*ALWAYS make sure you dispose of used antifreeze in accordance to your local laws!

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