A transmission fluid cooler for cooling the automatic transmission fluid of a motor vehicle equipped with an automatic transmission, and associated method. The transmission fluid cooler can include a fluid inlet tank, a fluid outlet tank, and a plurality of extruded aluminum heat transfer tubes connecting the inlet tank to the outlet tank. Each tube can include first and second substantially flat sidewalls, a plurality of internal webs extending between the first and second sidewalls, and a plurality of dimples and convolutions to cause turbulation and stirring of the transmission fluid in order to increase heat transfer.