Why does my ford focus have an antifreeze leak and when the motor is off why does the engine hiss ?
An antifreeze leak happens when there is a hole in the system. The system will still try to do its job and ends up creating pressure that causes a hissing sound when the engine is turned off. I’m sure it is hissing when the engine is running, just difficult to hear over the engine itself. Topping off the coolant level may eliminate the issue temporarily until you have time to have the leak repaired.