South Carolina has very mild winters but it still gets colds. That cold air will affect your MPG so when I saw my mileage drop by a good 8 MPG on cold mornings I decided to try to block some of the cold air from getting into the intake. I took this opportunity to also start some aerodynamic changes to the car.

Here's what the factory cold air intake system looks like (the front pipe extends to the pax fender and gets its cool air from the front of the car):

Here the mid pipe has been removed and the front pipe has a towel stuffed in it:

The grill before modification. Even though is may be hard to see in the pictures, note that the front bumper has been Bondo'd all to hell and resprayed by the previous owner. There is overspray on the turn signals and chunks of Bondo breaking off. I was definitely not worried about messing up this bumper:

For the test run I completely blocked off the front grill with some heavy plastic (like a thick plastic bag) and painters tape. Before you ask, I believe the modification would still be fine in a hot Charleston summer unless you were sitting around at idle at stoplights for long periods of time. I'm quite sure I will be modifying this page and my front grill block when the outside temps heat up though:

In the "been there, done that" department I had also tried this modification on my Mazda Miata. I had removed the supercharger a few months before blocking the grill so this was "kind of" a stock Miata at that point. With the grill blocked with the exception of a 6" hole in the middle I was able to control my engine temps (water temp) just fine. I could make the water temp start rising if I drove the car in 3rd gear @ 5,000 RPM for a mile or so but dropping back to 5th gear would immedately bring the temps back down. This testing was done in the hot August temps of Charleston. The difference between the engine load on my Miata gunning it @ 5,000 RPM and the 2,000 RPM 45 MPH cruising I do in the Metro is night and day.

After blocking off the front grill I saw my MPGs return to normal (or near normal) so I knew I was on the right path. I removed the plastic from the grill and threw it away. Two weeks later (I was a little lazy on this project) when it was time to make the "permanent" grill block I realized how stupid it was to have thrown away my template and had to make another one. I used some more plastic and a marker and drew a rough pattern to use for my metal grill block:

The metal I used was some old scrap that I had laying around for years. It measures 0.028" thick (21 gauge for aluminum). I wrote the 34" x 10 3/8" on it before I took the picture in case anyone needed that info. The brown stuff is a paper backing that is on the aluminum:

I attached it with sheet metal screws (drilled holes in the sheet metal first and then held it up to the bumper to drill through that):

You can see that it doesn't bend very nicely due to the bumper being such a strange shape. There is a gap at the bottom on both sides but I don't think that will hurt anything:

So, how is it working. Well, before the weather turned cold I was getting 58-64 MPG instantaneous on the flat cruising sections on my trip to work. When the weather turned cold I would see my first few minutes of driving dip down around the 35 MPG area and a few minutes later (when the car warmed up) I would see around 52 MPG. After fitting the front grill block I am back up to around 56-58 MPG. The cold weather is still hurting me but not as much as it would if I didn't have the grill block. The two weeks where there was no grill block on the car (in between the plastic and metal projects) my mileage dropped so I definitely did some A-B-A-B testing on the project. It works...

Oh, one more note. Charleston has strange weather and we will get a 40 degree day followed by a 75 degree day in the winter. I can see that there is still a difference in my MPG depending on the outside temperature. Further modifications are needed to combat this fluctuation in temps. I'll update the page as those modifications are completed.

Some ideas:
engine pan
warm air induction (getting warmth from the exhaust manifold)
electronic modification (resistor trick)