On aircraft powered by horizontally opposed engines, the winterization kit consists of two slotted sheet metal plates that are screwed to the front of the cowling, on either side of the prop spinner. The plates have slots cut in them, that restrict the amount of airflow over the cylinder head baffles and through the oil cooler. There should be something in the maintenance manual about this, as well as the OAT limits, but I seem to recall we never used them unless the OAT's got down below zero Fahrenheit. In cold weather (-30 -40) it may be necessary to close off the oil cooler completely. We used to use a piece of half-inch thick felt placed directly over the oil cooler.