Engine oil provides 60% of an engines cooling efficency ( antifreeze coolant, the remaining 40% ) , so a cooler oil would seem better, but really only efficent if the oil temp exceeds the optimum tempurture of the oil and gets too thin when hot, which is listed on the oil container, the colder oil becomes thicker, therefor you get more oil preassure, without the oil cooler, the oil would be thinner and have less preassure. It is not nessary, but won't hurt anything.