Dakkon made a great point above. If you follow this DIY you only swap a little over half the coolant. I appreciate the OP taking the time to put this together but I had to refer back to the Bentley as I was expecting to see 8.4 liters drain and I ended up getting about 4.5 liters.
If you read the linked DIY the OP replaces the drained coolant with 2.5 L of coolant and the same amount of distilled water. He puts in a total of 5 liters coolant.
The m54 and m52 (E46 2.5 & 3.0) engines have a coolant capacity of 8.4 liters.
You need to drain the engine block to get the remaining 3.5 liters out. It is a 13mm hex bolt on the exhaust side of the lower block below cylinder #2. (see photo). You will get another 3.5 L of coolant once you remove this drain plug. Put this plug back first, torquing to 25Nm (18ft/lbs) then follow the rest of the OP's DIY. Remember now that you will need an additional 3.5 L of coolant mixture.