Anyone know what that hose is/does? It has a small sucking/hissing sound when it starts to stall and die. Thanks.

 

Return heater hose

 

That hose would give you a coolant leak. If you are having a sucking sound, check for a vacuum leak. Manifold or brake booster.

 

Thanks guys. I had a coolant leak inside the manifold 6 months ago. My weep valve was clogged and the coolant leaked into the manifold and caused some damage. Mechanic fixed it up for me $800 but haven't had the leak anymore. New hose and other new things. Guess I will check it out. Thanks.