About 13 below zero at car starting time this morning and my old GMQ started right up with Mobil 1 High Mileage 5w30 in there, though there was a strange buzzing sound from the engine compartment for awhile. For some reason the engine fan kicked on and off for a bit too. I was wondering if the buzzing could have been coming from the bypass valve in the oil filter--it seemed to come from that vicinity, but hard to tell. In any case, all gauges read normal and everything worked fine, though it took quite a bit of time to get warmed up!