Where to start with a partial grill block

[Kodak]

Upper or lower?

Lately, I'm having all of these modding ideas - none of which I have actually pursued yet - but with winter coming, a partial grill block seems practical.

I'm thinking of maybe starting low and creating a design that acts like a door, allowing a closed position in the winter, and opened in the summer.

Or am I off base, and the upper (larger) grill is a better starting point?

[capnbass91]

I think I read somewhere that it is better to start lower. That's what I did and I saw an improvement in MPG. But I think putting a block on the upper grill would be more beneficial, that way would let air go over the car easier... well at least in my mind it makes sense haha. And on my car blocking the upper grill opening would be easier.

[ChazInMT]

Upper for sure, putting the air over the roof is better than under the truck.

[JRMichler]

I blocked the upper grille, the slot between the upper grille and the bumper, and the two lower holes on my Canyon. I left open the hole under/behind the front license plate.

The engine temperature has been unchanged at 186 to 190 deg F at temperatures up to 90 deg F with the air conditioner running. The engine fan clutch has not engaged once.

I really have to make some plastic grille blocks (similar to the fog light covers) to replace that two year old temporary blue masking tape.