-35 F in west central Indiana in the late '70s. And this temperature was recorded on an alcohol thermometer inside my garage. Had a 300 watt light bulb by the side of the engine all night and a blanket over the hood. The battery was inside over a heat vent and it still was hard to start. BTW, it was a Ford 2.3 4-cylinder with 10W-30 oil.
The morning this happened, Cincinnati, OH was -49 F, colder than the north slope of Alaska.