That's true, but oil enters as oil and exits as oil.
Transmission oil coolers, either the plate style or a quality tube and fin style, have the ability to tumble the oil as it passes through the cooler to give the oil maximum exposure to the cooling surfaces of the cooler. It's called the "skin effect". Quality tube and fin coolers like those from Hayden have an insert in each of the tubes the oil passes through and the design of the plate cooler is such that the insert to tumble the oil is not required. Cheap transmission coolers do not have these inserts inside the tube or if they do the insert is only in the intake/outlet of the cooler(a marketing ploy??). I know this because I've cut various cheap coolers apart in the past. I don't know if ac coolers have these inserts in them or not, as I've never cut one in half. Again, JMHO and a lot of years in the transmission parts supply industry.
