It certainly be interesting to monitor variation in air temperature all over the engine compartment. I know certain units have their own cooling fans but I am not sure where they draw their air from?? I assume most heat transfer would be be by localised air convection currents and direct radiation in particular from the exhaust manifold. Don't know the answers
just asking questions
I know there was a problem with the cooling capacity of the big engined V8 W126's in hotter climates which was rumoured to to associated with a lack of airflow "post radiator" Jim Forgione has details of cooling mods to the viscous fan to increase forced ventilation on his site.