What are the symptoms of a bad coolant bypass solenoid valve?

Symptoms of a bad coolant bypass solenoid valve include overheating of the engine, fluctuating engine temperatures, and poor heater performance. You may also notice a decrease in fuel efficiency and potential coolant leaks. Additionally, the check engine light may illuminate if the vehicle's diagnostic system detects an issue with the valve. If these symptoms occur, it's essential to have the system inspected to prevent further engine damage.