Are you by chance running an electric cooling fan in front of the radiator? Rip that sucker out or put it behind. When you have a fan in front of the core, the airflow, both running and freewheeling, will concentrate at the blade tips and you’ll only use a small percentage of the core area . The air will also get “turbulated”. The flow through the air side of the radiator is inversely proportional to the pressure drop across the core. Turbulent air has a pressure drop that goes as the square of the airflow, whereas laminar flow is linear. Turbulent air flow very much has its place in atomizing fuel or in transferring heat across certain surfaces, etc., but you want it laminar across the fins.
As far as cross-flow VS. down-flow, that’s a bit of a misnomer, but we’ll ignore that. All things being equal (core size, and available airflow), there is no difference. The core design with multiple passes and good coolant distribution is the key here.
Why does every modern car use a side entry radiator now if it’s just a matter of core design? The reason a lot of manufacturers went to
horizontal was initially because of the reduction in vehicle frontal height in modern cars, which require lower profile radiators. Also, if the manufacturer wants to increase the size of the core, a horizontal flow HX allows for the same headers and collectors, the only difference being longer tubes (or plates). In a down-flow radiator, it is unlikely that the height could be increased, so more columns of tubes would be required, increasing manufacturing cost. In the auto industry, they start to worry if cost goes up for something by more than a few cents. Hope that lends some guidance.
Here at the Classic Car Clinic, we have access to some extremely good modern high efficiency radiator cores which we have built into your existing radiator tanks and brackets, the result is a far superior cooling system yet retaining the original look of your radiator.
We also advocate the use of Evans Waterless Coolant in your cooling system.
Taken from the words of Lynette Soave, Roscoe, Illonois, USA. (Facebook).