[Christ]

Blow smoke into a bottle, then blow over the top of the bottle, from about 8 inches away... blow smoothly, not quickly. You can watch the smoke swirl in the bottle, and some will leave.

Kinda the same concept under a car in motion.

But wasn't the original cause for this action to keep it warmer while sitting, engine off?

I believe that was the reason for asking about the hood blanket and such, to insulate the bay a little more from the thermal losses WHILE SITTING, and without idling the engine to make it stay warmer, right?

For that purpose, there still may be some hope... but I'm pretty sure we'll find that the engine won't heat up anymore because you've further sealed the hood... Unless you have a full grille block, a mostly sealed belly pan, and a sealed hood.. then you may run into airflow issues, and the engine just might overheat with no place for the heat to go.

Fact is, no matter how much the average person blocks stuff off, there are still airgaps somewhere that are allowing airflow, and thus heat loss, somewhere on the car.