[C5Shark]

That 42mpg tank was with the car in completely stock trim with the exception of over-inflated tires.

I actually blocked the upper grill and left the lower untouched. The car has a digital readout in the scrollable driver information center which displays engine coolant temp, instant/average mpg, etc., etc.

After doing some hot weather driving it looks like I'll need to better control the airflow coming in through the lower opening as the cruising ECT has increased by 2-4 degrees. (Stock unblocked cruising ECT is 217F!!!). There is very little (more like nothing) in terms of baffling around the sides of the radiator to prevent air from going around it completely, so I will be looking to add something here to better direct airflow through the radiator instead of around it.

My trips are mostly highway. I drive about 30 miles round trip to work daily and I'd say about 18-20 miles of that are highway. I try to stay around 55-60 mph (despite getting blown away by traffic). I try to a little engine off coasting when I can but my route doesn't really allow for much of that. I feel that downshifting to keep the engine in DFCO while slowing is more effective for my route than actual EOC.