- Refer to the drain and fill procedure in this section, then drain the cooling system.
- Close the drain valve.
Your GM W-Body vehicle uses an aluminum radiator with plastic tanks, and the coolant comes into contact with numerous aluminum parts in the cooling system. Many coolant system flushing chemicals are extremely caustic and will attack aluminum parts. Make absolutely sure any chemical flushing solution is compatible with and safe to use with aluminum cooling system components. Follow the directions on the container.
- If using a flushing solution, remove the thermostat. Reinstall the thermostat housing.
- Add sufficient water to fill the system.
- Start the engine and run for a few minutes. Shut the engine OFF . Drain the cooling system.
- With the engine OFF , and if using a flushing solution, disconnect the heater hose to the heater core, usually at the firewall. Connect a water hose to end of the heater hose and run water into the system until it begins to flow out of the top of the radiator.
- Allow the water to flow out of the radiator until it is clear.
- Reconnect the heater hose.
- Drain the cooling system again.
- Reinstall the thermostat.
- Empty the coolant reservoir or surge tank and flush it.
- Fill the cooling system using the correct ratio of antifreeze and water, to the bottom of the radiator filler neck. Fill the reservoir or surge tank to the FULL mark.
- Install the radiator cap, making sure the arrows align with the overflow tube.