Clearances in the engine are all skewed. 10w-40 is more along the lines of peanut butter. Only the strongest antifreeze mixtures stay liquid. Brake fluid gets thick. Often cylinder head valves fail to seal because of contraction.
Tires can crack if impacted hard.
Door handles, seats and stuff are just waiting to snap. Fuel pump diaphragms may split when asked to flex. CV boots shatter commonly. In that kinda of cold you leave the rig running before the temps drop that far, and don't shut it off. In the more reasonable 20-30 below range that we're seeing here where I'm at, most of this isn't a problem.