A radiator is simply a heat exchanger- - - -energy released by burning fuel goes three directions, through the transmission and drivetrain to move the vehicle, out the exhaust, and dissipated by the cooling system. Ideally, if we could capture and use all the thermal energy burning the fuel releases, we could get three times the gas mileage. The problem is, the energy is released much faster than it can be trapped and applied to the powertrain. That's one reason turbocharged vehicles make lots of power with tiny engines- - - -at least some of the thermal energy that would normally get wasted out the tailpipe gets recycled back into the engine in the form of higher manifold pressure created by the spinning turbine- - - -driven by exhaust energy.
The cooling system is tasked with getting rid of enough energy to prevent the engine from overheating and destroying itself. This can be done directly by making the cylinder walls thin, adding fins, and blowing lots of air over them, or indirectly by absorbing the heat with a liquid, piping it to a heat exchanger (AKA "radiator") and blowing air over the radiator. It doesn't matter if the coolant flows up, down, sideways, or backwards as long as there's enough area for the liquid/air heat transfer to happen. Cross flow radiators are more a function of the body style the engine is installed in, rather than the direction the coolant flows. Long, low vehicles with wedge-shaped hoods can use a wide, angled cross flow radiator to good advantage while something tall and big like a Peterbilt tractor will have a fairly narrow downflow cooling system. Bottom line- - - -it's more about the volume of coolant, how fast it flows through the heat exchanger, and how many square inches of area there is for the air to contact. Blowing lots of high speed air over a relatively small radiator might keep a big, powerful engine cool, but in general, bigger is better where radiators are concerned, no matter what direction the coolant flows.
Jerry
