Yeah, those cold starts in Miami really get tough on engines with the oil too thick... sometimes you'll have to take the oil out and replace it with clear H20 just to get it thin enough to allow the engine to turn over in those frigid Miami midwinters. Some Miamians have seen the necessity of connecting in a second battery (not in series, just parallel) to double their cold cranking amps rating, just to have enough energy to run the glowplugs for a minute and a half and then let the starter fight the engine over and over and over, before it FINALLY starts, just when things are starting to look pretty grim.... the pengins are starting to prowl around the car, looking for their next meal when you finally freeze because the diesel had gelled...
OH, please.
Rotella dino 15w40 or synthetic if you prefer... 15w40 is a good weight for you, it'll keep some of the leaks down and not get too thin in the hot weather. Run it year-round.