What type of coolant do I use for my 1999 323i BMW

Hello, BMW specifies the use of BMW engine coolant, but there are a few brands that are approved by the manufacturer for use. These brands will vary by year and model, as the engine coolant is formulated for the materials used to manufacture the engine. All coolant is not created equal, and mixing some coolants can lead to leaks, overheating, and component malfunction. That being said, if the reservior is empty, and there is no way to identify the type of engine coolant in the cooling system, you may want to consider flushing the system out, finding and repairing the issue causeing coolant loss, and refill with a BMW approved product. If you only need a small amount of coolant, and do not wish to track down the leak, you can add distilled water to the reservior and it will blend with the existing coolant. This may decrease the engine coolant's ability to perform it's job.