Parking in the sun on a hot summer day
 

Does the trunk stay cooler than the cabin?

If you are directly in the sun, then yes. The trunk is dark and shaded where as the cabin will heat up extremely hot if you dont have a sun shade on the front windshield.

Iirc (which is not a solid assumption to be making) the cabin will heat up and cool down more rapidly than the trunk. I mean there's probably factors like fuel mass and hot exhausts etc, but we'll ignore them.



The cabin basically has shitty insulation and very little thermal mass

The trunk is doing better because of no windows

The engine bay would be the slowest to heat up and cool down because of the giant thermal mass (iron engine) and no glass. Although it isn't sealed so air currents can pass through.



short answer: it depends