why does grill blocking work? aero or heat?

[jwxr7]

Just my 2 cents

grill blocking looks like a good idea , and I want to eventually try it. My only concern is about allowing enough cooling air to still get thru to keep the electric fan from coming on more than usual. On my little car that fan really drags the engine down thru the alternator when it comes on. I could see a point where a grill block's aero gains could be canceled out by a larger electrical load. This would probably happen at lower speeds where the aero would have less effect anyways. If it is really warm out it could happen at higher speeds. Each type of car would be different, and in each type of climate. It would be interesting to test FE loss from the fan running vs gain from grill block aero. I like the idea of movable louvers for the grill block, like I saw in another thread here. Heck, my 55 allis chalmers could come with an optional movable louvered front grill for cold weather use (not too much for aero since it only goes 14mph ).