3.8l Poor Gas Mileage

[AUGrad]

Well I feel like a total idiot now. My cruise back from Florida was definitely probably averaging 80 mph among those long stretches. That was probably why it was so low Guess I didn’t expect a few MPH to effect the MPG that much. Not my brightest moment I guess

No need to call yourself names. Speed isn't the only factor, but wind resistance increase isn't linear. This morning was probably ideal circumstances for me too - cool air temperature, light traffic, etc.

 

[sidewinder1]

Well I feel like a total idiot now. My cruise back from Florida was definitely probably averaging 80 mph among those long stretches. That was probably why it was so low Guess I didn’t expect a few MPH to effect the MPG that much. Not my brightest moment I guess

fyi...epa testing never exceed 60

Mpg For Speed - Fuel Efficiency Vs. Speed

How much?
According to studies backed by the department of energy, the average car will be at its advertised MPG at 55 mph. But as the speed increases:

- 3% less efficient at 60 mph
- 8% less efficient at 65 mph
- 17% less efficient at 70 mph
- 23% less efficient at 75 mph
- 28% less efficient at 80 mph

 

[EdP]

fyi...epa testing never exceed 60



Mpg For Speed - Fuel Efficiency Vs. Speed

How much?
According to studies backed by the department of energy, the average car will be at its advertised MPG at 55 mph. But as the speed increases:

- 3% less efficient at 60 mph
- 8% less efficient at 65 mph
- 17% less efficient at 70 mph
- 23% less efficient at 75 mph
- 28% less efficient at 80 mph

Those numbers sound about right from a crude test that I did a few years back. I had the "Instant MPG" on a LeSabre so I checked it on the same stretch of road on the way to work in the morning. Speed really killed the economy. I tried for 55 mph but even with barely any traffic it made me a menace on the highway at that slow of a speed.

 

[STL_Genesis]

That’s good but your range still shows over 300 miles still... you can’t really get a good average that early in a tank. I’d be interested to know what it says when you get down around 150/100 though!

Yeah... Peoria is only 190 miles away. I used cruise and was only about 7 over the limit, so pretty gentle. I might trek out to Colorado this summer. That would be a good test.

 

[EdP]

Yeah... Peoria is only 190 miles away. I used cruise and was only about 7 over the limit, so pretty gentle. I might trek out to Colorado this summer. That would be a good test.

Check both ways. Colorado is uphill.

 

[zape]

fyi...epa testing never exceed 60

Mpg For Speed - Fuel Efficiency Vs. Speed

How much?
According to studies backed by the department of energy, the average car will be at its advertised MPG at 55 mph. But as the speed increases:

- 3% less efficient at 60 mph
- 8% less efficient at 65 mph
- 17% less efficient at 70 mph
- 23% less efficient at 75 mph
- 28% less efficient at 80 mph

Saved time is also money. Need a better formula with pay/h and gas price as input parameters

 

[pmckechnie]

I got a question for someone smarter than I. (Oh, thats everyone).
If MPG drops as speed go up, how do the MBs,BMWs,etc get from one exit on the autobahn in Germany to the next when driving 150 to 180 mph or more. I know that my 1984 500SEL has a recommended 155 mph max for an extended time. That is not the max speed. I have been on the autobahn before but not in my MB but I believe 150 mph would be very easy for it.

 

[TurtleBoy]

^ It drops but doesn't go to zero. The M5 has a 20 gallon tank and rated for 21mpg highway. Let's say driving at autobahn the mpg drops by 75% (that is just a guess), you still would be able to drive around 100 miles. They have a lot of service areas on it so filling up isn't a problem.

 

[EdP]

I got a question for someone smarter than I. (Oh, thats everyone).
If MPG drops as speed go up, how do the MBs,BMWs,etc get from one exit on the autobahn in Germany to the next when driving 150 to 180 mph or more. I know that my 1984 500SEL has a recommended 155 mph max for an extended time. That is not the max speed. I have been on the autobahn before but not in my MB but I believe 150 mph would be very easy for it.

I could not make up my mide, should I buy a G80 or Bugatti Veyron. I ended up with the G80 only because it get better fuel mileage.
I found this:
Run the 1,000 hp Bugatti Veyron Grand Sport at top speed and it will empty its 26.4-gallon fuel tank in 12 minutes. The Vitesse, with its extra 200 hp, will do it in 10.3, which is lucky actually because Michelin won't guarantee the tires to run above 250 mph for more than 15 minutes.”

 

[J Dixon]

Well I feel like a total idiot now. My cruise back from Florida was definitely probably averaging 80 mph among those long stretches. That was probably why it was so low Guess I didn’t expect a few MPH to effect the MPG that much. Not my brightest moment I guess

Don't feel bad. Every car has its sweet spot for MPG. I find my 2015 5.0 does best at highway speeds of 70-75 mph AND also at 45-ish mph IF the pace can be maintained and not stop-n-go. Heck, here in NC, I would take the same route to the beach and get slightly better mileage heading east (down in elevation) than returning west (up to about 1000ft above sea level). It's always in the details, ya know?

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[FlySwatter]

I could not make up my mide, should I buy a G80 or Bugatti Veyron. I ended up with the G80 only because it get better fuel mileage.
I found this:
Run the 1,000 hp Bugatti Veyron Grand Sport at top speed and it will empty its 26.4-gallon fuel tank in 12 minutes. The Vitesse, with its extra 200 hp, will do it in 10.3, which is lucky actually because Michelin won't guarantee the tires to run above 250 mph for more than 15 minutes.”

I think we've all had to make the hard decision like this ... Fortunately for me, I have Forza Horizon to fill in the gaps

 

[Andyj]

I bet one lap in the Bugatti costs more than the whole G80, so mileage? Meh. Great post.

 

[Xul0279]

Amusing thread. The last thing I bought my Genesis for is great gas mileage. My 3.8L AWD can eke out 24 mpg blasting down the highway at 80 on long trips with the cruise control on. Around town I’m in the mid-to-upper teens, but on the decidedly lower end of that scale when I keep my foot in her a bit more than usual.

None of that matters in the least when I back Two Ton Tessie out of my garage. All that really matter is the smiles-per-gallon I record as I revel in the pleasures of my amazingly serene and decidedly understated beauty, as I slink down the road in my supremely comfortable and sneaky powerful rolling cone of silence.

Lost in the sonic joy of that marvelous Lexicon sound machine, soothed by a blessedly quite backdrop and bathing in the glorious sunlight of my panoramic splendor, I can’t imagine driving anything else. That’s my Gennie and I don’t give a damn if she’s a thirsty girl - she’s a keeper!

I just slow clapped in my living room. I need a tissue.

 

[need4spd]

Yeah speed really does effect MPG, just back from a 5 hour trip each way and averaged around 29mpg each way with an average speed of 72mph.

PS at 65mph (55 zone) and flat ground I was getting 31mpg for about 50 miles, I was shocked. 34psi cold, Michelin PS AS3+ so a more sticky tire than OEM (=more rolling resistance/reduction in mpg)

 

[Xul0279]

I average 22 MPG in town using ECO mode.
I'm not in a hurry to get anywhere.

 

[Starflyer]

I've never gotten more than 25 mpg on the highway, ECO or not. Also, check the door jam on that tire pressure.

The only way to tell accurate gas mileage is the old fashion way, segment miles divided by gallons add (assuming a full tank to start). Over several cars, I've found them to be in error up to at least 3 MPG (reading high). I've had about 6 highway runs of over 100 miles and normally my onboard computer says I'm getting 26-30 MPG, but I haven't checked the old fashion way and assume my reports are on the high side.

 

[FlySwatter]

The only way to tell accurate gas mileage is the old fashion way, segment miles divided by gallons add (assuming a full tank to start). Over several cars, I've found them to be in error up to at least 3 MPG (reading high). I've had about 6 highway runs of over 100 miles and normally my onboard computer says I'm getting 26-30 MPG, but I haven't checked the old fashion way and assume my reports are on the high side.

Yep, I pay little attention to the computer estimate other than the "live" value which I can use to self regulate my own eco driving if I feel like doing so. The computer estimate has a very large asterisk attached; to the tune of 2 to 3 mph over actual in my experience. I use fuelly.com to track my mileage; not becuase I can't figure it myself, but because it's a convenient place to save my history.

 

[jimmy buoy]

As a comparison, I just drove my AWD 5.0 from Florida to Ontario Canada and averaged 22mpg for the total trip. That trip included three separate hour long traffic jams on major interstates, through mountains in Virginia and West Virginia, and even a couple of hours in hilly backroads with 10MPH turns and hills that you can't see over until you crest the tops - a thrill... but not the best for max fuel economy. Total of 1370 miles took 62 gal (filled up the car before starting the trip, during, and filled it at the end of the trip. Simple math - no computers to mess up. The car's trunk was fully loaded so the two of us were running rather heavy and speeds averaged from 55MPH to 80MPH+.

Given the comfort and ease of driving with the various options like smart cruise and lane keeping assistance, I'm rather pleased with the performance. The worst fuel usage comes with cold weather and short trips in town, but that's no big surprise either for this heavy, effortlessly powerful vehicle.

 

[Hawaii 5ooohhhh]

.. Fortunately for me, I have Forza Horizon to fill in the gaps

Thx...PS4 folks are sad now

 

[Skeezix]

Very glad I found this thread. I just got a job transfer from Houston to Minneapolis and will have to get an AWD car. I'll be driving 30K-40K miles a year, and get mileage reimbursement. Consequently, I have been intently researching the G80 in AWD/3.8 configuration. I was hoping to achieve 25-27 mpg on the highway at 65-70mph with a 3.8 with HTRAC and 87 octane fuel. (I will be forced to drive like a grandma, as my driving is monitored).