Oil coolers become necessary if you consistantly run
oil temps over 250 degrees F or 120 degrees C. There are 2 basic types,
oil to air and oil to water heat exchanger.
If you have a cooler and run temps under 180 degrees or about 80C you need to block off the cooler. Having to low a temp will destroy your engine faster than to high a temp. This is because the oil is working within it's operating temp for proper lubrication.
This is the advantage of oil to water heat exchangers. The coolent will heat the oil up but keeps it at a consistant temp when hammering on the car.