Sorry for a dumb question about my 2013 RDX: what is this hose under rear left fender liner splash shield for? Is it kind of a spout for water?

 

A/C drain

 

It's in the rear left fender, so is it more likely an A/C drain or a sunroof drain?

IDK RDXs or if they have sunroofs.


Either way, the hoses should be kept open.

 

Yep. Hose from the evaporator inside the car to drain condensed water that gathers when the AC is functioning. Back in the day, some cars simply had a container of some sort under the evaporator that the water would fall into and eventually evaporate. If you left the AC on too long, it would overflow and you'd get water on the floor.

To confirm, run your AC for a while, then park. You'll see a little puddle under the passenger side after a few minutes. Some people freak out that they're leaking something but it's simply the water draining - often from melted ice - that comes from the AC evaporator after you shut off the car.

 

I was gonna say fuel tank vent. My 2014 dribbles water from the AC up front not from the rear fender well.

 

No fuel tank vent.Closed system in the US.

 

Ah yes, of course..

 

Maybe the drain at the fuel filler. There is a small hole just under the filler pipe at the fuel cap.