I agree with using synthetic. It will be just fine sitting idle (no degradation). Running is better than sitting idle. The condensation (water) in the oil is a problem. Short, cold (engine temp) drives murder an engine. I worked at Amoco Research labs the year they did the 10W-40 in Buick odd fire V-6 trials (late 70's). They called it the 'old lady test'. They drove a dozen or so Buicks (Regals, I think) for very short trips (a mile or two) then parked the cars for a a few hours, rinse & repeat. They ran them for about a year, drained the oil, tore down the engines & inspected same. Then the worst bits were put on display. The remaining engines were re-assembled, installed in the cars, and the cars were auctioned off. The oil was a lumpy, runny, tar like sludge. The badly worn bits included cams, mains, piston skirts, and wrist pins. One or two oil pumps seized on the sludge. This was with dino oil, 10W-40 (SD I think). Same oil used in Chevy 305's in taxi's (multi-year 10W-40 oil test fleet in suburban Chicago area cabs) went the distance (100K) without destroying the engines.