Hotter than a three dollar pistol.
Extremely hot to the point of physical displeasure or burning. Derived from 19th century American slang referring to a cheap pistol assembled from mismatching parts with improper tolerances, which when fired became very hot due to poor ignition and burning of the powder charge, and projectile friction from a misaligned chamber and barrel.
My car had been sitting in the sun with the windows up, and when I got inside the steering wheel was hotter than a three dollar pistol.