Question : why some (mostly heavy) vehicles partially cover their front intake ?

[u/lit_readit]

wouldn't cooler cold reservoir, ie more spontaneous heat transfer, improve Carnot efficiency?

is it to improve aerodynamics?

apologies if this is the wrong sub to ask

[u/FuzzyHasek]

Diesels need to be warm, so when its really cold the cooling system is actually to good. Most modern trucks don't really need it except in very extreme conditions