MINI Recommends the coolant system drain and refill EVERY 4 YEARS as listed in the 'Additional Service Items' section of Inspection II. This will maximize longevity of the cooling system and its components.
The following procedure is for 2002-2006 R50 MINI Cooper and R53 Cooper S, and 2005-2008 R52 MINI Cooper and S Convertibles.
Best done with a cold engine, or wait until the engine has cooled sufficiently. Wait until the engine cools!!
1. Remove radiator cap.
2. Remove lower hose from radiator, and heater hoses at bulkhead. USE CAUTION WHEN COOLANT IS HOT.
3. Reinstall hoses after coolant has drained.
4. Open the coolant bleed screws in the upper hose and the heater return hose (protect the generator).
5. Fill the engine with MINI Cooper Antifreeze (50/50 mix) through thermostat housing (expansion coolant tank in the Cooper S).
6. Close bleed screws when air free coolant flows.
7. Continue to fill through thermostat housing (or expansion tank).
8. Fill expansions tank to 'Max'.
9. Start engine and run at idle. Top up coolant as necessary.
10. Turn off engine and install pressure cap.