How do transformer oil coolers improve heat dissipation?

Oil coolers increase the surface area and enhance convection or forced flow to move heat from the oil to ambient air or water. In ONAN designs, radiators allow natural circulation of warm oil upward and cooled oil downward. In forced systems such as ONAF, fans increase air flow across radiators, and in OFAF or OFWF designs, pumps force oil through coolers and fans or water heat exchangers remove heat efficiently. Effective cooling lowers winding hot spot temperature and extends insulation life.