Big S - I don't know how you use your 911 but if it is used often in the winter you should at least run 10W40 if not something lower. The reason I say this is that the weather could take a turn for the worst while your car is out. This logic also applies if you don't have a heated garage. Right now it is between 10 and 25F here in the midwest. It takes my car a good half hour to warm up to thermostat-opening temps. I run 10W40 all year round. The lighter oil will also make life easier on your starter and battery in the winter. Every little bit helps. My daily ride (V8 S10) gets a 5W30 change every thanksgiving. I notice the change in morning start-up immediately. I don't like that it takes so long for the P-car to warm up in the winter, but unless I water cool it this won't change.
