Use only BMW recommended coolant.
Only use BMW coolant and distilled water.
The type of coolant recommended for a 2003 BMW 525i is Glysantin G48. You can purchase this at an auto parts store or a BMW dealership.
In the coolant reservoir in front of the engine.
BMW coolant from dealer. It is blue in color and can be purchase fairly cheap at any BMW dealer ship. Around $20 for a gallon. Hope this helps.
The coolant for a BMW x5 is placed into the coolant overflow tank on the left side of the engine compartment. It should be filled to the full mark when the engine is at operating temperature.
BMW 530i's owners manual recommends and all season water coolant be used in its automobiles. It does not specify which brand to use.
In the radiator
A 2001 BMW 325i has two coolant temperature sensors. They constantly monitor the temperature and adjust flow as needed.
All BMWs use a ethylene glycol based coolant, anything compatible with the green coolant will suffice, however BMW o.e coolant is blue, but still glycol based none the less.
the wet kind
Well, it will no light up if you have the correct coolant levels.