[Dmitry at Pelican Parts]

How much have you added? Is the car's thermostat indicating that it's going to overheat? You may have a faulty thermostat if there is no issue. Have the codes read; it'll give you a great place to start. In case you need to replace your thermostat, I've attached a DIY tech article below.

BMW E90 Thermostat Replacement | E91, E92, E93 | Pelican Parts DIY Maintenance Article