I've gotten in the 60+ mpg range this way (~67 mpg IIRC), but the trip was only a portion of the tank. The rest was back to the short, hilly daily commute. I don't see that sort of mileage drop until about 70 mph. 60 mph is a relatively efficient zone. At 75 mph cruise control the average was 43-45 mpg in mild weather.
The car was already warmed up and 57% grill blocked...but earlier today I got 72 mpg on a six mile trip at 19 F. I hit the lights and traffic pretty well so I didn't waste much on the hilly commute. Speeds were in the 35-45 mph range mostly. I'm leaning toward blocking two more of the bottom slats for the winter. This would equate to ~86% grill block (6 of 7.) I would do just one more, but the insulation spans two slats perfectly.
Just to bring this thread back to life.. i'm running 40+ PSI in the tires, grill is blocked, right now it's -10 degree's Celcius here, (that's about 14F). Car is having a hell of a time keeping warm - even with the grill blocked, i'm hoping that I will get better in the spring. I got a SGII for x-mas this year, and it's installed, still trying to figure out how the SGII can help me, obviously the temp and IGN helps. I try to keep it below 17IGN when possible, try to keep below 2000RPM as much as possible. So far I think it's helping. What's the next step? I do alot of highway here, and in Canada our highways are limited at 62MPH. Most people drive 70-75 MPH. However I have come to realize that economy pretty much goes out the window as soon as you get anywhere over 65, and speed is clearly you enemy here. I find that cruise control on the highway tends to be the best option, unless in traffic. So far doing most of my testing - the #1 thing you can do to increase your fuel economy is slow down. I see many people here asking what they can do to get better mileage, all the little things we do probably help -- a bit -- but speed, acceleration is probably 80% of what you need to do... On the comment of Ethanol - our gas in Canada has it, no question, is there a place to get non-ethanol fuel? Any comments?
I usually take it easy on my first mile getting out of my neighborhood and then speed picks up to 40 mph. I've learned from this forum not to turn on the heater for the 1st 5 minutes, so I have been doing that lately. My mpg has dropped a little but not bad at all.