So done some investigating, tracing the route of the airflow after it goes through the radiator on my car. I've long suspected the exit route is out the front wheel wells; the front underfloor of the Dart is very well sealed and the swirling wheel is an enticing source of low pressure relative to the slow moving radiator exit air bumping around in the engine bay.
So the air exits the radiator (image bottom), plows into the turbo and transverse block (image center), and then out and into the low pressure area of the very inviting front wheel well (not pictured):
So you understand where we're looking, into the wheel well of the RH wheel, the leading side of the wheel well, inboard:
Amongst all this rabble is an outlet. It's not particularly well defined, but the opening (where the half shaft pokes out) is much larger than would needs be if it wasn't doing double duty. And there is further evidence that my hunch is correct (see image below):
There is a gurney on the trailing edge of the leading wheel well exit. This works to enhance the low pressure draw.
I've flirted with increasing the height of that gurney, the idea being that it draws even more air through the radiator, lowering temps, and causing the active grill shutters to be closed more often. But I suspect the gurney is already sized to achieve close to that, so I'm on the fence.
Anyhow, thought this might be enlightening to some, the airflow path of the cooling system. The cooling system produces roughly 1/3 of a car's total drag (the other being the underfloor, 1/3, and the exterior shape, also 1/3), so it's important to look at all aspects. Surprisingly the Dart's inlet side is actually pretty good, I've sealed up a few inlet-to-radiator gaps (very small gaps), but that's about all that can be done there. The let down is the exit, but there is precious little that can be done given the architecture and confined space.