[geodosch]

Bob, I did some grill blocking a couple of weeks ago. After several 20ºF mornings, I saw my trip mileage drop from almost 60 to where I was struggling to hit 50 on the drive to work (~35 miles, mostly Interstate).

I used the same method I'd used on my 2007, which was to use gray foam pipe insulation tucked into the fins on the lower intake. On my '07 I blocked the top intake for all but the hottest weather, though from what I've read I don't plan to block that at all on my 2010. I used 1 piece, which blocks about 75%. After blocking my mileage was back in the mid-high 50's on very cold days, and 60+ when it got a bit milder (low 40's).

IMHO, grill blocking is most important for the initial warm-up phase, when MPG suffers the most. Unfortunately for my commute in the morning, I have moderate speeds with some, or a lot (depending upon traffic) of stop and go at the start of my trip, which means my ICE is always running to warm itself up, so the sooner I can get it warmed-up, the better. By the time I'm on the freeway it's already warmed-up. The blocking is also very helpful for continued stop&go driving, since it prevents the ICE from cooling down quickly. However and constant highway speeds, keeping the cooling system warm isn't as much of a problem, and there's also little if any opportunity for the ICE to shutdown anyway.