99 Jetta: overheating

I have the newer version 1999 Jetta (so it looks like the 2000's).
It has a 2.0L gasoline engine, automatic trans. I have semi-recently replaced the plugs and wires but nothing else had been done too recently.

Lately, it started overheating. I do smell coolant and there is some visible sitting in a few places in the engine. I think it may be a hose but I cant ever see any fluid coming out. The weird thing is is that the reserve tank has plenty of fluid in it, and I've checked the hoses to the radiator and the top one gets hot when the car is running so I dont think the thermostat is stuck. Although I noticed that the bottom radiator hose is fairly cool when the car is running (but I assumed this was normal as thats what a radiator is supposed to do). When the car is running I can hear a hissing sound like air escaping from a hose or something, but its not spraying anything that I can see, and I cant find where the hissing is coming from.

Any ideas? Thanks.

The thermostat is near the water pump at the lower hose. The lower hose should get warm too (a little cooler than the upper hose). You might need to pressure test the system to find the leak, unfortunately not many people keep the adapter to fit that tank. The most common place for it to leak is at the plastic coolant pipe that mounts to the left side of the cylinder head just above the transmission. It's the one with the sensors plugged into it and the upper radiator hose & about another smaller hose. The plastic begins to break down under the heat. Your local dealer will keep these in stock if you need it.

Thanks! Thats exactly where I think it's coming from as the coolant appears to be sitting on the transmission. I appreciate your help.