Will an upper grille block do squat?
 

Here is my situation, it's very cold out right now but it might get above freezing soon so I can do a little work on my pickup truck (Chevy S10).

My 4WD went out (push button selector not engaging system), I currently suspect the vacuum assisted components GM thoughtfully placed under the battery tray (which can leak battery acid down there) but chasing that possible leak down can be complex I'm told.

Therefore as a temporary measure I added four more 70 lb bags of tube sand to the two I already had in the truck bed - that's nearly 500 lbs of sand plus the weight of fuel. I'm not going to get stuck easily.

As you can imagine "the get up an go - went up and left" my truck, and I suspect the gas mileage is soon to follow.

I don't drive a lot but I can try to up my gas mileage with a partial grille bock.

Here is the truck.
http://i184.photobucket.com/albums/x...psx85zvetc.jpg
http://i184.photobucket.com/albums/x...p/IMGP0363.jpg
http://i184.photobucket.com/albums/x...psdd244397.jpg

As you can see the tow hook locations are sealed, and the radiator can get no air from underneath.

Question is, will an upper only grille block do squat?

I would be leaving the lower slit open.

Yes I have an electric fan installed, would not even consider this if it still had the old mechanical fan clutch.

I would do a grille block. In winter it's fine. Watch your temps. Use synthetics for engine oil and transmission since those keep temps down. Using some good quality extra heavy duty coolant will help in that department too.
Cold Front Grille Insert 1998 to 2003 Chevy S10 Pickup or Chevy Blazer#88475 | eBay

If you wanna do more on aero, do a coroplast belly pan from old election sign if you have friends in politics. Then get some smaller mirrors.
For 94-01 S10 F1 Manual Adjustable Chrome Finish Side View Mirror | eBay

Get a wiper cowl too...
Lund 25505 Polycarbonate Smoke Shadow Wiper Cowl for Sonoma/Jimmy/Bravada/S10 | eBay

Then you can get into friction modifiers for the engine, differential, wheel bearings using NMF and/or tungsten disulfide from lowerfriction.com

Have fun.

and get a tonneau if you don't have...
Extang 2560: Black Max Tonneau Cover S10/S15 1994-2003, 6" short bed Isuzu Hombre | JEGS

and an extruded tailgate lip will help a bit too
Chevy S10 1994-2003 Wingswest Urethane 3 pc rear tailgate spoiler No light | eBay

...except that one's too big but you get the idea. You wanna trip the air to slow it down before separation.

You will know when you drive in the rain/snow and you notice how much wake is behind you. You'll be slicing through the air.

sorry and do an antenna relocate too since that doesn't need to be flapping out there...
GOLF CART HIDDEN STYLE AM FM AMPLIFYED ANTENNA,.. BRAND NEW + How Too Install | eBay

...and for your original traction problem, you might want some real tires for colder weather. Nokian WRG3 or Hakkapeliitta for winter.

Cheap insurance

That's quite the list there spdfrk, very thoughtful of you.

Of that list I've either already done it, or I am too frugal with my time and money to do it.

The upper grille block is quick and easy, I can do that next day above freezing.

I need tires, saving up for some Cooper Discoverer STT Pro's, better rated in snow than BF Goodrich and Goodyear AT's, plus designed and made in USA.

Today and tomorrow it supposed to get up to 36-37 degrees F...................spend the time, or a waste of time?

It's going to take me longer to dig my coroplast (black color) out of storage than to do the block it's self.

Maybe this is a two day project, dig out the supplies today, do the work tomorrow.

I have a lot of other things to do, but quick little projects like this seem to charge me up.

I say do it. Seeing the radiator setup, instead of doing just an upper grill block, I would block the center and right (vehicle right, picture left) sections on both the top and bottom. That leaves you the (vehicle) left side open for cooling and what I assume is a transmission cooling line to get air and cooling as well. At your wintertime temps, that will be more than enough to cool the engine down when it finally gets up to thermostat temp.

I'd do it.

upper block
 

When GM is serious about drag reduction they go with the upper block
http://i1271.photobucket.com/albums/...itled-14_2.jpg
So does Ford
http://i1271.photobucket.com/albums/...itled-13_3.jpg
http://i1271.photobucket.com/albums/...titled-9_2.jpg
http://i1271.photobucket.com/albums/...titled1_44.jpg

http://i1271.photobucket.com/albums/...titled2_41.jpg
NASCAR
http://i1271.photobucket.com/albums/...itled24_10.jpg
This GM LSR pickup has a 100% block
http://i1271.photobucket.com/albums/...titled28_6.jpg
You don't have any internal ductwork,and the distance between the heat exchanger and grille isn't large,so be careful.