A few days ago, we emerged from a polar vortex that drifted south - a textbook example of what those things do from time to time. The associated cold managed to get the media into full cry and revived all of the how cold is it? jokes. Judging from Internet aviation forums, it also got a lot of pilots concerned about starting their airplanes and raised the pertinent seasonal question as to what is cold for a piston engine. At what temperature are you risking damage to your engine if you start it without some sort of preheating?
This is a companion discussion topic for the original entry at https://www.avweb.com/ownership/whats-cold-for-a-piston-aircraft-engine