Here is the method I use for a good coolant flush.

1. Drain fluid from radiator and engine block
2. Remove the thermostat
3. Reinstall the t-stat housing and upper radiator hose
4. Disconnect upper radiator hose at radiator
5. Flush system with garden hose through upper radiator hose until water runs clear
6. Disconnect heater hoses, open heat valve
7. Flush heater core
8. Flush overflow tank
9. Run engine for a bit during flushing to get the fluid from the water pump and other dead spaces.
10. Drain as much water as possible from cooling system
11. Run a shorter flush with distilled water to displace the tap water
12. Siphon water from overflow tank
13. Reinstall thermostat
14. Button everything back up
15. Refill cooling system with specified amount of antifreeze, bring up to level with water, preferably distilled. The amount of antifreeze you need can be calculated from the published cooling capacity for your vehicle.
16. Run car, top off coolant
17. Keep adding water as required every morning until system is topped off.

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95 E320 Cabriolet, 169K