[AaronM]

Well, the owners manual says 20W50 is good down to about 15 degrees Fahrenheit, so I'm going to say that you're just fine without worrying about covering the oil cooler at any temp above 15 degrees Fahrenheit.

The main concern in cold temps isn't that the oil won't get up to temperature (as long as the coolant is getting to temp, the oil will too), but rather the ability to flow during the first few seconds of a cold start. Covering or uncovering the oil cooler isn't going to do a damn thing about flow on cold start. The only thing that's going to help you there is a block heater.

If you're really, truly paranoid, move to 10W40 for the winter. The manual says that's good down to about -5 Fahrenheit, so you'll be covered for any weather you'll realistically see in PA.