This looks like a small radiator used to cool off the engine oil or the automatic transmission fluid . As air passes through the cooler, the temperature of the oil in the cooler is reduced. Some units reduce the temperature of the manual gearbox and differential lubricants in racing cars.
OIL COOLER
Meaning of OIL COOLER in English
English dictionary of automotive terms. Английский словарь автомобильных терминов. 2012