Real World MPG Numbers?

[hondoford]

I bought my 3.8 on Dec. 18th and have 5,000 miles on it already. I do about 80% highway and 20% city. On the last 3 tanks I have driven between 440 and 475 miles per tank and I'm averaging between 25.3 and 26.5 mpg. I'm very impressed with the mileage this thing is getting!

I traded in a '08 Subaru WRX STi and a '08 Sonata GLS for my Genesis sedan. The Sonata was a 4 cyl and driving the same route I was able to regularly get 29 mpg but it had no guts at all. The Subaru most of the time was in violation of the speed limit but the best mileage I was able to get was approx. 21 mpg.

 

[GripperDon]

City town driving only, Regular gas. Very consistant 18.2 to 18.5 2500 miles on car.

 

[dataguy]

Took my second road trip of any decent length (Los Angeles to Las Vegas), which for those who drive I-15 knows that it's characterized by high speeds, occasionally heavy traffic, gusty winds, temperature variations, and several up-and-down climbs from around 900 to 4800 feet.

LA to LV (about 265 miles): 27.2 MPG (vs. trip computer average of 27.5)
LV to LA: 29.0 MPG (vs. trip computer average of 28.5)

Calculation method was odometer mileage divided by gallons pumped. Air conditioning and audio ran non-stop. Speeds ranged from 5mph to 90mph, averaging around 65mph.

Interestingly, the return trip would have gotten even better mileage if it wasn't for the 35 miles of stop and go traffic (all of us Californians returning on Sunday) from Vegas to Primm. Must be the fuel formulation difference between California and Nevada...

 

[ASHDUMP]

I just did a 680mi round trip from MA to PA to visit a friend. On my way down I got about 26MPG and on my way home I got about 27.5MPG according to the Genesis. I actually got up to 28.1MPG for the first 200mi on the way home and the last 140 it dropped down. I'm still on the same tank and doing a lot of city driving so its now down to 25.4MPG. I predict it will get down to 24 or 23MPG the next time I fill her up. I'm SUPER impressed with the MPG I'm getting with the V8.

 

[mcginnpm]

I'm ranging from a low of 15.2 to a high of 26.0 with an average of 19.2 MPG. The attached PDF is a distribution of my MPG distributions after 10K miles and 30 fill-ups (all my fill-ups are "full tanks"...between 15.9 and 18 gal). The majority of my driving is "in-town" and "mid-range" trips. All my high MPG's were from interstate driving.

 

[Disaster]

About 650 miles on the odometer of our V6. First tank full measured 21.5mpg, in mostly highway driving (though short/15 mile trips.) The fuel mileage gauge read an optimistic 22.7mpg. This makes sense since the speedo reads a bit high. I was expecting a little better mileage.

Now at almost 3K on the odometer, and warmer weather, the mileage has improved a bit. My wife got 24.1mpg on the last tankful. This was measured. I can't recall what the computer guessed the mileage was.

 

[redswd]

I have about 2800 miles on mine. Brand new and in the winter it was 14-15 in town 23-24 highway. Now it's 16+ in town and on a trip back from Omaha, no hills to speak of mostly river grade, I held it at 70 and got 28.8 actual. The computer tends to be 1-2 tenths higher than my calculations and it read 29. A trip to Kansas City yesterday yielded 27 mpg computer with a scant amount of town driving on both ends and highway speed 75 and 2 on ramp blasts just for fun.

 

[nearwater]

I use an application through my iPhone where it calculates the MPG numbers and keep track of it including gas prices.
My first pump went 18.15MPG which was 99% city driving.
The second pump was 19.94MPG which was about 50/50 city/highway driving with 4 adults in the cabin all the time. And I wasn't easy on the gas.

Seems like it's getting better mileage than my old Corvette, which is lighter and has a LOT more torque, basically the engine idling when cruising down the highway.
My Vette did about 28MPG on the highway w/ 2 occupants, hatch full of luggage, and doing about 70~85 most of the time.
That was on Kentucky/Tennessee mountain area.

Dan

 

[Genny46PM]

I have about 1450 miles on it now.
With 90% surface street/10% freeway driving, she's averaging about 18.5 mpg. 90% freeway/10% surface street driving, she does about 22 mpg. But on the freeway, I do substantial amount of triple digit speed driving. I think she will yield 24-25 mpg if I can drive at steady 75-80 mph.

 

[JimInNashville]

I'm driving a base 3.8, largely in a suburban commute that is 65% HWY, 35% city.
After 1000 miles, I'm averaging slightly more than 23mpg. The past week, I left slightly earlier, encountered less traffic, and rang up 120 miles at 24.4mpg.

My preceding car was a Honda Accord 6, 240hp, which got about 22.5mpg under identical conditions. The Accord was a great car. (Kept me in one piece despite being totaled by a texting teenager.) However, the Accord felt positively tinny compared to the Genesis. And as nice a performer as the Accord was, it was not even in the same league as the Genesis.

The fact that the Genesis actually gets better mileage than my Accord literally amazes me. But, quite simply, it does, and there is no denying it.

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[JimInNashville]

Not knowing for sure, but I would guess that it has to do with how the G's computer rounds the actual figure (in other words, to how many digits after the decimal point), as compared to how we may actually enter the figures into a calculator. The discrepancy in the figures indicates to me that this is probably the reason. We would be more inclined to input maybe one or two digits (to the tenth or to the one-hundredths), and the computer may actually compute it out to 10, 20 or more digits--even though it doesn't show on the dash.

EPA estimates, and our own driving habits, number of passengers, terrain, use of air conditioning or open windows, whether in traffic or on the open road, etc....all of these things dramatically affect our gas mileage, small as the number difference may actually be....thus the 'wisdom' of a certain presidential candidate telling us to check our air pressure....when maybe it's "his" air pressure that should be checked....(and I'm not referring to his tires...).

I'm getting consistently 25-27 hwy., and approx. 20 combined. For a car of this size/power, etc., I'm very pleased. I got the same numbers from my slightly lesser-powered Azera (263 hp, 3.8V6 front-wheel drive), and also from a previous Mazda Millenia (2.5V6...170-ish hp, if memory serves)...which was considerably under-powered, IMO. I should note that, particularly in the warmer weather (about 9 mos/year in East Tennessee), I typically drive with the A/C on. With the compressor disengaged in cooler weather, I would expect the numbers to improve slightly.

Dan

As a statistician, let me remind y'all that, when you fill a gas tank, even if you are careful and try to be consistent, there are substantial variations in how full you actually get the tank. These minor discrepancies can, in practice, alter the estimated "gas used" by as much as half a gallon, even if you fill up in the same station and the same pump.

So, for example, if you drive 100 miles and estimate that you "use 4.5 gallons", you may have used 5 gallons or 4, or any amount in-between, depending on exactly how full you got the tank during the last two times you filled up. I've seen people go nuts over a "30mpg tank" that actually represented getting the tank really, reallly full the last time, then not topping it off this time.

Consequently, any time you compute "real mileage" by filling up your tank and doing a subtraction, you are incorporating an error of measurement. This error of measurement has a bigger impact on "estimatated mileage" when the number of miles driven is smaller.

As a consequence, it is not at all surprising that the trip computer will give a reading lower than the "real" mileage some of the time, and higher than the "real mileage" other times, and that the differences can be quite substantial on any single tank of gas.

On the other hand, if you keep careful records, after 5000 miles you'll have an excellent idea what your true mileage is. I can already definitively state that my base Genesis 3.8 sedan gets better mileage than my Honda Accord 6.

 

[ASHDUMP]

I'm a topper offer.... The people behind me get upset.... at least I'm paying with a gas card and not going to the booth to pay. That bugs me.

 

[mcginnpm]

As a statistician, let me remind y'all that, when you fill a gas tank, even if you are careful and try to be consistent, there are substantial variations in how full you actually get the tank.

Jim the stat-man in Nashville hits the nail on the head. Unless you've got a sight glass installed to where you can fill the tank up to exactly the the same level every time, doing the old "divide miles driven by gallons pumped" can inject some inaccuracies, upwards of about 5%.

The onboard computer number is probaby more accurate. The computer tells the fuel injectors when to open and when to close to get that magic fuel/air mixture that the O2 sensors are checking. It knows the fuel pressure. So it probaby knows how much fuel got squirted into each cylinder. Add all those squirts up, divide the miles driven by that total, and you've probably got the more accurate MPG for that tank specific tank of gas. Of course the computer can have errors too. How accurate is the fuel pressure? How clean are the fuel injectors?

 

[redswd]

I think that we would all agree MPG figures as computed by the average driver is not an exact science. Yet we probably would all agree it is desirable to go as many miles as possible without refilling the gas tank. What I'm experiencing and what I think I'm hearing from most of you is that you are confident your Genesis is, for a large luxury sedan, surprisingly economical. That coupled with the warranty, price point, build quality and reliability makes me very happy!

 

[Disaster]

As a statistician, let me remind y'all that, when you fill a gas tank, even if you are careful and try to be consistent, there are substantial variations in how full you actually get the tank. These minor discrepancies can, in practice, alter the estimated "gas used" by as much as half a gallon, even if you fill up in the same station and the same pump.

So, for example, if you drive 100 miles and estimate that you "use 4.5 gallons", you may have used 5 gallons or 4, or any amount in-between, depending on exactly how full you got the tank during the last two times you filled up. I've seen people go nuts over a "30mpg tank" that actually represented getting the tank really, reallly full the last time, then not topping it off this time.

Consequently, any time you compute "real mileage" by filling up your tank and doing a subtraction, you are incorporating an error of measurement. This error of measurement has a bigger impact on "estimatated mileage" when the number of miles driven is smaller.

As a consequence, it is not at all surprising that the trip computer will give a reading lower than the "real" mileage some of the time, and higher than the "real mileage" other times, and that the differences can be quite substantial on any single tank of gas.

On the other hand, if you keep careful records, after 5000 miles you'll have an excellent idea what your true mileage is. I can already definitively state that my base Genesis 3.8 sedan gets better mileage than my Honda Accord 6.

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.

 

[rdunegan]

2009 3.8L with 17460 miles.

Just returned from 3-week 5947 mile jaunt and averaged 26.88 mpg ... as advertised (27 highway). Travelled from NC to FL to Dallas to Tucson to Albuquerque to Los Alamos & Santa Fe to Amarillo etc Nashville to NC. Included some major headwinds and tailwinds.

Included mix of hundreds of Interstate miles at 80+ mph, about 50 miles unpaved Navajo roads, many two-lane paved roads up to 9000 feet elevation with snow. Tank fill mpg ranged from 24.1 to 29.5. GPS recorded max speed of 91 mph (only once!) on I-40. Used cruise control a lot.

Genesis did very well especially on mountain roads. Got really filthy and dripped dirty water into trunk when opened. Needs a power port that stays "hot" all the time for charging phones, etc, and a definite place to store sun glasses.

Did not see another Genesis the entire trip! Where ARE they hiding??

 

[bradyb]

I got terrible MPG because I kept ogling the tech package while in the garage

Seem to be getting around 18 mpg with city driving... 24 hwy.

@ simonwpb> I am so there! I cant keep my hands off the Tek and Lexi! after 2,800 miles im getting around 26-27 with my v8. thats combined town and fwy! I plan on some mods like cat back exhaust(borla) k and N filter, and synthetic oil. Im hoping for a 4-6 percentile increase!

 

[ASHDUMP]

My 4.6 is about average. I get killer highway MPG but when I hit the city it kills it. I'm not that hard on the engine either. I would say 26/27 MPG on the highway and 20 in the city...

Do you guys use any additives in the gas tank?

 

[Disaster]

My 4.6 is about average. I get killer highway MPG but when I hit the city it kills it. I'm not that hard on the engine either. I would say
26/27 MPG on the highway and 20 in the city...

20 is really good for a 375hp V8. Just got 22.13mpg on our last tank full with V6...mostly 17 minute drives to and from work...2 minutes to highway, 13 minutes on highway...then 1 minute back off highway. Got 22.5mpg on the previous tank. I suspect the first 2-3 minutes of driving is fuel wasting emissions warmup.

Do you guys use any additives in the gas tank?

Additives are not a good idea. They can be rough on the emissions systems. If you use decent gasoline it has all the additive, built in, you need.

 

[redswd]

What about those performance proms for your computer? Any validity to mpg/hp claims? Will they void your warranty?