Several years ago I did a very UN-scientific comparison of several hydraulic fluids at -25F. I was surprised at how viscous even ATF was.

I suspect that this demo was at least -20F

Still, cold is such a subjective term. I remember leaving South Dakota at -13F and arriving at San Francisco at +65F and as we were taking our coats off we watched airport workers wearing heavier parkas than we had and thinking they were going to freeze to death! But then again I get uncomfortable at anything over +105F!