The calculation is based on the EPA ratings of 40/38 and the percentages that you set in your profile. You have 25/75 set so 40x.25 + 38x.75 = 38.5. So once your overall total average based on all the tanks you have entered is at or above 38.5 and you have more than 3000 miles of mileage data entered you will get your star. If you enter tank data that brings your total tank average below 38.5 your star will go away. Your signature shows that you are at exactly 38.5 that is why you have a star not that you have entered 3000 miles of data of above 39.1 (though that is what helped get you to your current total of 38.5)

If I wanted to get my star back right now I could change my profile percentage to 10/90 city/hwy which would mean that 38.2 mpg would get a star. Even if I did that though with the 36 mpg tanks that it looks like I'll be getting through most of the winter that will keep pulling my total tank average down. Once your average is below 38 even setting your profile to 100 percent hwy you won't have a star.

What I'll need to get my star back is to have a number of tanks that will bring my overall average above 38.5 mpg. I don't see this happening until warmer weather comes back to northern Illinois. Based on the temperatures you've entered with your tank data you should not have any problems keeping your star.