What symptom will occur if a vehicle's cooling system thermostat is stuck in the fully open position?

1. The engine will overheat within 5 minutes of starting.
2. The engine will take too long to reach operating temperature, and cabin-heater output may be weak, especially in cold weather.
3. Coolant will leak directly into the engine cylinders.
4. The engine's fuel efficiency will increase due to the cooler cylinder walls.