No, 50wt is not a bad vicousity. There are plenty of racers who run the stuff. I didn't know you only drive the car in the summer. Still, if it were me, I'd consider installing an oil heater for use on chilly days. But I'm anal-retentive. I knew a guy in high school (very long time ago) who spun a bearing on a chilly day (probably about 40-50 degrees) by not allowing the engine to warm up before he punched the throttle. He was using straight 50wt non-synthetic.