For topping up - even in warm weather - use only a mixture of antifreeze concentrate and clean, lime-free water.
Note: To continue driving, you can also, especially in summer, fill it with clean water. However, at the earliest opportunity, you should adjust the concentration of the composition with antifreeze.
Models 518i, 520i, 525i: When the engine is cold (coolant temperature around +20°C), the coolant level should be at the mark on the expansion tank or slightly higher.
Models 530i, 535i, 524td, 525td/tds: When the engine is cold (coolant temperature around +20°C), the coolant level should be at the mark on the expansion tank.
To avoid engine damage, add cold coolant to a cold engine.
Caution: When the engine is hot, open the cap carefully. Risk of injury! Place a rag when opening. If possible, open the cap when the coolant temperature is below +90°C.
When opening the lid, first unscrew it a little to release the pressure. Then completely unscrew and remove the lid.
If the coolant level drops rapidly, perform an external inspection for leaks.
(The original version is on the portal: BMWMAN.ru)