Engine coolant is usually water-based, but may also be oil. The radiator transfers the heat from the fluid inside to the air outside, thereby indirect evaporative cooling pdf the fluid, which in turn cools the engine. Radiators are typically mounted in a position where they receive airflow from the forward movement of the vehicle, such as behind a front grill.
Where engines are mid- or rear-mounted, it is common to mount the radiator behind a front grill to achieve sufficient airflow, even though this requires long coolant pipes. Alternatively, the radiator may draw air from the flow over the top of the vehicle or from a side-mounted grill. For long vehicles, such as buses, side airflow is most common for engine and transmission cooling and top airflow most common for air conditioner cooling. Automobile radiators are constructed of a pair of header tanks, linked by a core with many narrow passageways, giving a high surface area relative to volume. This core is usually made of stacked layers of metal sheet, pressed to form channels and soldered or brazed together. For many years radiators were made from brass or copper cores soldered to brass headers.
Modern radiators have aluminum cores, and often save money and weight by using plastic headers. This construction is more prone to failure and less easily repaired than traditional materials. An earlier construction method was the honeycomb radiator. Round tubes were swaged into hexagons at their ends, then stacked together and soldered. As they only touched at their ends, this formed what became in effect a solid water tank with many air tubes through it. Some vintage cars use radiator cores made from coiled tube, a less efficient but simpler construction. A sectioned view of the cylinder block, radiator and connecting hoses.