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About a third of fuel energy leaves through the coolant. Flow follows from Q = m cp deltaT with a 50/50 glycol mix at about 3.6 kJ/kg·K, and the airflow needed depends on the temperature difference between coolant and ambient — which is why cooling is marginal on hot days.
Cooling load
heat = power x rejection fraction; flow = heat / (cp x deltaT); airflow = heat / (rho cp deltaT_air)
Airflow through the core depends on road speed or the fan. Stationary, only the fan provides it, and at high ambient the temperature difference is small.
Only if airflow is available. Core thickness beyond about 40 mm gives diminishing returns because the air heats up passing through the first rows.