Q: Steam is coming out of coolant reservoir.

Hello. If your coolant overflow tank is steaming and overflowing, then that means the vehicle is running hotter than normal, and may even be overheating. The vehicle will need to be inspected for possible overheating issues and any repairs can be done by a certified mechanic. As cooling system problems can sometimes be elusive, I would recommend having the vehicle checked and tested by a professional technician, such as one from YourMechanic, to determine the exact nature of the problem.