LV,
First check the ducting to the oil cooler. If you hover over freshly cut grass, I have found that they tend to collect a bit of it. As for the aux oil cooler, as far as i am concerned, it should be a mandatory item for the turboed models as the oil temps will run higher in the turbocharged engines. for those who also operate in areas where temperatures can be on the cool side during the winter, you can put a small damper over a small portion of the oil cooler to help warm up the oil.