2007 Ford Fusion 2.3L I4.  115,000mi.

Pour some black pepper in your radiator. I swear it works better than Stops Leak.

Pressure test cooling system

Turn your vent to recirculation not outside air and see if you can still detect it. You may be smelling the reservoir vapor. through the vent.

Just because your heater works, doesn't mean you don't have a heater core leak.  Pressure test the coolant system.

This.  

Ive also had minor leaks under hood produce a coolant smell.   Just fixed a Mercedes for a family friend that had a coolant smell.   Dealership diagnosed as a faulty heater core.   3k to fix.   Turns out it was just the water pump seeping onto the belt,  slinging coolant everywhere.

Exactly. Check your heater inlet/outlet hoses. They tend to develop tears/cracks at the ends past the retaining clip.

Look at the ac drain . A lot of times a heater core will drip out of the ac drain and not into the floor

Please stop giving advice.

If you want to create a bigger issue, put shit in your radiator. Barsleak or what ever else will work, MAYBE, but I grantee it will give you bigger issues down the road. The only time I would EVER use "mechanic in a bottle" is if you are just trying to limp a car along untill you can buy a new one in a few months.
If the coolant smell is coming through the air vents I would say it could be a heater core/ connection at heater core issue. Pressure test the system and leave pressure on it for a while, it really doenst take much of a leak for someone whos paying attention to smell it. Also you may not get coolant on the floor boards, most modern cars have a heater box drain to the outside, if you see any coolant residue on that drain, youll find more in the box. However I will say pay attention to ALL coolant lines and even the radiator for leaks. I have seen trucks at work with coolant leaks on radiator hoses and drivers tell me its a heater core, also I know for a fact that my personal pickup has a coolant leak at the radiator fill neck, and I smell coolant in the cab quite often.

It's funny though, we (another pilot and I) had to do that one night to our old, beat-up Company station wagon.  It was our regular nightly mode of transportation from the airport to our apartment and back.  It had a radiator leak one night and, of course, no place was open.  In a pinch, the other guy, who owned/built race cars, put some pepper in to get us through until morning.  It held for at least a year, and probably longer after I left the company.  



 

GM added stop leak from the factory to its V-8 Northstar engine to prevent seepage through porous engine blocks.   It was crushed  ginger root pellets.   FYI...   Bars Leak sells a very similar product that works really well for minor leaks,  without clogging up heater cores.