Been thinking about this for a while, the counter current aka counter flow radiator is the most efficient heat exchanger layout.
The cooling flow enters where the cooled flow exits and the cooling flow exits where the cooled flow enters, this allows for maximum transfer of heat and a much smaller radiator can be used.
Cars have a crossflow radiator, the two flows are perpendicular, the air passing through the top of radiator works well and removes lots of heat, but the air passing through the bottom is mostly wasted because temperature gradient is very low.
With airflow already restricted with a grill block, I wonder if it would be more effective to actually block off the bottom half of the radiator and force twice as much air through the top half which has a much higher temp gradient.
The paper below talks about a number of aspects of radiator design and also has some discussion on thermal managment in motor vehicles in it's introduction.
http://www.energy.lth.se/fileadmin/e...Lin_110928.pdf