Why are carmakers blocking the lower grille, not the top? (OEM active grille blocks)

[99LeCouch]

They want the coolant returning to the engine to be hotter for better FE. The radiators I've seen have the coolant return at the bottom (there are exceptions, but I can't think of any). Blocking the lower part will keep air from cooling the coolant more than it already cooled up top, so the engine computer can inject less fuel while keeping engine temperatures up.

That sounds logical and sensical to me. Takers?

[Thymeclock]

On my '09 Aveo I have permanently blocked the lower grille with no adverse effect. For the upper grille I made a removable grille block that I use only in winter. I also have permanently installed a under belly pan. When I bought the car as new there was nothing at all there - everything in front and underneath was one big, wide open area: no aerodynamic benefit, no heat retention.

Remember, when you are stuck in traffic your car isn't moving, but it IS producing heat. Heat rises, and something needs to be left open for adequate ventilation in warm weather, so it's better to keep open the upper grille. If everything is blocked, you will tend to run too hot in summer. If the frontal area is just one big, wide open space you will wait a long time in winter for the car to reach operating temperature and your FE will suffer. It's a balance, or a trade off.

[euromodder]

Originally Posted by Daox

The Focus grill is almost entirely blocked on the top. The only real opening is the bottom

From what I'm seeing on this side of the Atlantic, it's usually the upper grille or upper portion of the grille that gets blocked.


Grille size has indeed become excessive - but huge parts of those massive grilles are actually blocked off.
So it's purely a (very debatable) style thing.
Personally, I think it's but ugly.

[DonR]

I suppose if the upper grille is mostly blocked any way, it makes sense. I never looked at any of the models with the active grille blocks in person.