Oh, so I should be safe! The temperature when I left was 32 degrees. It is now almost 60. I would've been a little annoyed if I had to remove it within one day. Thanks again! 52.5 mpg in 32 degree weather with just the top grills blocked is a little absurd. I'm very happy with these results.
Yes, that is absurd, but you just keep on it! I've been maintaining 45 with the grill blocked. Although my last tank was an absolutely dismal 37. I don't what happened there... It's hard to maintain MPG with multiple drivers, and my better half has a lead foot. She has told me however, that even she notices a difference with the grill block.
Here's the MFD in the afternoon after my commute (30-some miles round trip). ***An EBH would probably put that over 60, I'd think . . .