Real World MPG Numbers?

[JimInNashville]

Very true, but obviously related to how much gas is in the tank when you fill it. We rarely fill the tank if it is more than a quarter full (unless we are planning on a trip.) More often, I fill the tank with less than 100 miles left on it...often with less than 40. We also always fill at the same station...though not necessarily the same pump, but common pump design does reduce variability.

The 3.8L has a 19.3 gallon tank. Our usual refill is 16-18 gallons. Worst case for us then would be .5 gallon error on 16 gallons, 3%. The difference we were consistently seeing between estimated and actual was about 4%...and that was pretty consistent and NEVER was the estimated mileage less than the actual.

Having said that, there are some other variables that make the mileage I'm getting not a great longer term estimator. The following are some of the variables I can think of, vehicle break-in...still have less than 3K on the clock, weather...as temps warm up, mileage will change, tires...going from winter to summer tires will effect mileage, getting accustomed to vehicle...driving will change after get used to vehicle.

Point well taken. I should add that, if you maintain records, none of this matters once the miles add up. Eventually, if you record every gallon you put in the tank, you'll have an accurate mileage estimate. On the other hand, for a single fillup, you'll obviously have less sampling error in the mileage estimate if you let the tank get more empty. (A potential side benefit -- on average you'll be moving less weight, since you'll be moving less gasoline in your tank. This may actually yield a slight increase in gas mileage.)


BTW, comparing real mileage with the trip computer: My experience concurs with yours. My trip computer overestimates the mileage, probably by about 1 mpg.

 

[Disaster]

...if you maintain records, none of this matters once the miles add up. Eventually, if you record every gallon you put in the tank, you'll have an accurate mileage estimate. On the other hand, for a single fillup, you'll obviously have less sampling error in the mileage estimate if you let the tank get more empty. (A potential side benefit -- on average you'll be moving less weight, since you'll be moving less gasoline in your tank. This may actually yield a slight increase in gas mileage.)

For an overall average lifetime measuring is by far the most accurate, but you still need to do tankfuls to tell how it does city vs. highway. Also, measuring the fuel mileage regularly can help you spot when something is amiss, like low tire pressure, or old spark plugs. This is probably less important in modern cars, with all their monitors.

BTW, comparing real mileage with the trip computer: My experience concurs with yours. My trip computer overestimates the mileage, probably by about 1 mpg.

Interestingly, the mileage estimate is getting closer to the actual mileage, as we put more miles on the car. I wonder if there is some type of learning algorithm involved?

 

[Disaster]

Got our highest mileage so far, 230 mile trip with mixed city and highway driving coupled with a couple trips back and forth to work, 26.7mpg. Interestingly, for the first time, the computer's estimate was low, at 25.4mpg. This might be because we had a couple days of city driving after the trip that drove it down.

 

[Jerome Leff]

We have 8600 miles on Genny and it amazes me the gas milage that we get on the open road. Our last trip to Wilmington, Delaware, Albany, NY, Occoquan,Virginia, and home to Charlotte, NC., we averaged over 28 miles per gallon. It was filled every time to the brim and the gallons against the millage calculated. My wife and I could hardly believe it. We checked and double checked our figures. In some areas we were cruising over 80 miles per hour and still got excellant millage. In NC we do not have any ethanol mixed in with our fuel so, on my first fill up I got 30.6 miles per gallon. After that in other states with 10 % ethanol mixed in I still got over 28 miles per gallon. Love our Genny. Genny loves the open road.

 

[JDC]

Well, finally got in a 170 highway only trip, avg 70 MPH on cruise all the time and MPG was 26.5 with the V8. I have 800 miles on the car, so I don't think the mileage will improve at this point.

 

[zimmy]

Does using regular vs premium gas make any difference in those mileage numbers on the V8?

 

[cschuler]

Been getting 20 to 26 (city to trips). Have done as high as 28 on a trip. Must have been a helpful tailwind. I drive (set the cruise) at posted speeds +. Slower highway speeds, obviously yield better mileage.

Interesting note: We put 100,000 miles on a 2002 Lincoln Town Car and now almost 10,000 miles on our V6 Genny and the LTC was not too shabby, by comparison. I mention this because some seem to think that eight years makes a big difference in improved efficiency but I just don't see it. The LTC is bigger and heavier (but compared to the Genny, seriously underpowered).

I am happy with the Genny's mileage, but not ecstatic.

 

[mcginnpm]

Does using regular vs premium gas make any difference in those mileage numbers on the V8?

Not really. Premium = extra power in an engine designed for premium gas. Premium gas has a higher octane and thus will not detonate (i.e., pre-ignite or "knock") as early as regular gas will, thus you can "romp" on it more heavily (which means you are probably burning up your gas big time, so mileage will suck anyways).

Premium gas is particularly important for turbo charged engines as a higher boost can be obtained with premium. Most turbos have a "knock sensor" that will retard the boost when "knocking" occurs.