3.8l Poor Gas Mileage

[sidewinder1]

Now, I recently made a 10 hour drive to Florida and on the way back barely averaged under 25mpg with 95% hwy driving. I drove intentionally with a very light foot to try to boost this with it on ECO mode. Air pressure was 50psi all the way around (per tire's rating). With the HWY rating supposedly at 29 MPG I wanted to see if this is normal for anyone else??

Some anomalies I'm questioning. The car was about 60% into its oil change, with 3k miles on the air filter, so shouldnt have any effect. One thing I noticed was the big lower plastic tray protecting the engine is missing.... could the aero have an impact like this? And of course the "higher" mileage at 75k miles...

epa testing is done in a lab and is a general guide. real world will not always line up with lab results. speed, wind direction/speed, # of passengers, tire pressure, temperature, etc....etc will all be variables. as others have said, your mileage sounds about right . and don't forget to drop that air pressure

 

[jimbrown618]

I sympathize with your unhappiness for the gas mileage you are getting....but as others have said it is a heavy car; I have just acquired a 2015 AWD 5.0 for the past three weeks and yes it likes gasoline but seeing that it weighs 5710 lbs (yours is only 310 +/- lbs lighter...) there is no way I will ever say to my friends "Gee.....this Genesis gets really great gas mileage..."

 

[TurtleBoy]

I have just acquired a 2015 AWD 5.0 for the past three weeks and yes it likes gasoline but seeing that it weighs 5710 lbs (yours is only 310 +/- lbs lighter...) there is no way I will ever say to my friends "Gee.....this Genesis gets really great gas mileage..."

Isn't it "only" about 4,588 lbs?

 

[jimbrown618]

This what is in my manual.....maybe weight varies a bit depending on other factors but online sources are usually close to this... (sorry for the bad formatting...)

GROSS VEHICLE WEIGHT - KG (LBS)
Lambda 3.8 Tau 5.0
2WD AWD 2WD AWD
2,440 (5,379) 2,500 (5,511) 2,520 (5,556) 2,590 (5,710

GVW includes weight of fuel, passengers so other sources may list lower numbers that don't include these...

 

[Hueydriver]

That is way too high. That is a max pressure not a suggestion for what you should set the pressure at. The pressure listed on the door will in theory give you the best ride although some folks add a few pounds.

On my 3.8 the pressure calls for 33psi. I run them at 36 since day one.

 

[TurtleBoy]

This what is in my manual.....maybe weight varies a bit depending on other factors but online sources are usually close to this... (sorry for the bad formatting...)

GROSS VEHICLE WEIGHT - KG (LBS)
Lambda 3.8 Tau 5.0
2WD AWD 2WD AWD
2,440 (5,379) 2,500 (5,511) 2,520 (5,556) 2,590 (5,710

That is the gross vehicle weight, not the curb weight of the vehicle. The GVW would be the maximum amount of weight a vehicle can handle.

The curb weight of the 2015 V8 is listed at 4,588 on MT.

 

[jimbrown618]

That is the gross vehicle weight, not the curb weight of the vehicle. The GVW would be the maximum amount of weight a vehicle can handle.

The curb weight of the 2015 V8 is listed at 4,588 on MT.

Ok....

 

[Mr. Incredible]

So much for the 29MPG HWY rating. As for the tire pressure, I go off of what the tire suggests. Its rated at a max of 50psi so I set it at about 46/47 and the heat from driving brings it up to 50ish.

MAX PSI IS NOT RECOMMENDED PSI.


your recommended PSI is on the sticker on the inside of the drivers door jam I believe it is 35 psi for the 3.8L

MAX is only used if you are loading up the car, like towing or fully loaded passengers and trunk to the max cargo weight, you air up the tires to offset the excessive weight.

over inflating the tires to 50PSI will kill your tire wear..

 

[Boostpyro]

epa testing is done in a lab and is a general guide. real world will not always line up with lab results. speed, wind direction/speed, # of passengers, tire pressure, temperature, etc....etc will all be variables. as others have said, your mileage sounds about right . and don't forget to drop that air pressure

Yeah, of course it’s situational. I didn’t even expect to get what was recommended... I just thought it was odd I could barely get 5mpg under the recomended driving so carefully. But if that’s the general consensus I’ll just enjoy it for what it is. I love the car, it’s been really great so far.

I really wish there were more aftermarket support so I could tinker with it more

 

[Mr. Incredible]

Yeah, of course it’s situational. I didn’t even expect to get what was recommended... I just thought it was odd I could barely get 5mpg under the recomended driving so carefully. But if that’s the general consensus I’ll just enjoy it for what it is. I love the car, it’s been really great so far.

I really wish there were more aftermarket support so I could tinker with it more

something to consider:

disconnect the battery for a period of time 20-30 minutes, and reset the computers.

the computer in the car that estimates MPG is not perfect, in fact when I first got my G80 Sport I was complaining about how incredibly inaccurate it was when compared to a manual calculation (miles/gallons) In my Sport I get on average 360 miles to a tank, when I fill the tank takes approx. 17 gallons every time (between 17.2 and 17.7) as I typically fill within a few miles of the low fuel light coming on.

Manual calculation shows 360/17 = 21.17 mpg however the computer in the car for accumulated shows 18.5 - 18.7. it also estimated 490 miles to the tank when I refilled, but I never get above 360, and at 360 and 17 gallons there is approx. 2.5 - 3.0 gallons left in the tank if we are to believe the specs that the tank has 20 gallon tank adding 21.17 mpg to the 3 gallons gives me another 63.5 miles, for a total of roughly 425 miles NOT 490 miles.

So fast forward several months, I am rear ended and the car is at the body shop for 5 weeks, since the accident damaged the spare tire well where the battery sits, the battery had to be removed to weld in the new well.

When I got the car back, the computers were completely reset, and I mean completely, the DIS and GPS were in Korean, luckily I have extended family that speak/read Korean and they were able to get the systems back in English, the dealer couldn't. But since that time, since the reset, the DIS calculation has been almost spot on. it is registering 19.9 mpg average, and 390 miles to a tank at fill.

When I bought my car the dealer did a dealer trade with another dealer 200 miles away, they drove the car from that dealer to mine, I believe that long trip elevated the overall calculations and the battery reset force the computer to relearn based on my driving commute/style.

it is entirely possible the previous owner had a heavy foot and the computer is still calculating based of their driving style, and while driving conservatively with help adjust the averages, they won't be reporting true (for you) because of the long history of a different driving style.

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[Gebop]

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!

 

[Scokeing]

OP, i echo @Gebop comments above.
I too can validate you MPG values, my 2015 3.8 RWD 30k 33psi, mostly highway 70mph driving. Dash data recorder says 26+ MPG & 55 mph between fills, actual calculated is 24.5 MPG so I think it’s typical this this vehicle, as stated previously, it’s a very heavy car, providing a very smooth and quiet ride. I have very few issues wth this sedan and enjoy the ride.

 

[J Dixon]

Lots of discussion about tire pressure, but I never noticed WHAT tires you are running. Don't despair, the rolling resistance of certain tires does indeed have an effect on MPG, as well as new versus older tires. It is possible that you could see an increase in MPG with your next set of tires (or a decrease). I have personally witnessed a change of up to about 2 MPG with a tire swap on other cars I've owned.
I'd also say that using quality gas and fuel treatments (I like Chevron), has always given me peace of mind that the intake side of the engine is working efficiently. With 75K, it might be a consideration to have the intake/injectors cared for. I would recommend having it done professionally though. With all the computer wizardry in these cars, the days of shade tree mechanic work is a gamble.

My 5.0 averages about 21 MPG in mixed driving and I have touched 28.4 MPG on a flat highway run where I averaged around 75 MPH. That tells me there is probably some room to improve your mileage. Just keep hunting!

Good luck.

 

[need4spd]

I have AWD and on longer all highway trips - greater than 2 hours I get 27-29MPG, also I reset it once I get up to highway speed, and this is with some hills. This is at 60-65mph. If at 65-75 it drops to 24 or 25mpg.

I run 34-35PSI all around, 1-2 higher than recomended (3.8l AWD)

What speed were you driving?

Around town I don't break 19mpg

I believe the AWD is rated 25 and RWD is 26 or 27MPG, not 29MPG like you were saying.

 

[STL_Genesis]

Took a trip from St. Louis, MO up to Peoria, IL over the weekend. Almost managed a car reported 29mpg. I assume the car reports an accurate reading. Getting close to 29 MPG is pretty decent for a 4,300 lbs. 3.8 AWD in my book.

 

[Nikhil Malhotra]

Took a trip from St. Louis, MO up to Peoria, IL over the weekend. Almost managed a car reported 29mpg. I assume the car reports an accurate reading. Getting close to 29 MPG is pretty decent for a 4,300 lbs. 3.8 AWD in my book.

Cool . I've never seen north of 24mpg on my 3.8 .
I'm ok with 22-23 mpg average mileage in city / highway mixed driving - afterall California voted Yes for Prop 6 .

 

[rickkapur]

Hi

Cool . I've never seen north of 24mpg on my 3.8 .
I'm ok with 22-23 mpg average mileage in city / highway mixed driving - afterall California voted Yes for Prop 6 .

Hi Nikhil, are you in the Bay area by any chance? I am in San Jose; and would be good to get a Genesis group locally here to swap learning's and maybe hold a rally or something someday

 

[AUGrad]

No mention of speed? That has a significant impact on MPG. I regularly drive my 2015 3.8 RWD about 100 miles nonstop interstate, typically setting the cruise at 77mph, and get 26.0 MPG. This morning, I set the cruise on 74, and got 29.1 MPG.

 

[Boostpyro]

Took a trip from St. Louis, MO up to Peoria, IL over the weekend. Almost managed a car reported 29mpg. I assume the car reports an accurate reading. Getting close to 29 MPG is pretty decent for a 4,300 lbs. 3.8 AWD in my book.

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!

 

[Boostpyro]

No mention of speed? That has a significant impact on MPG. I regularly drive my 2015 3.8 RWD about 100 miles nonstop interstate, typically setting the cruise at 77mph, and get 26.0 MPG. This morning, I set the cruise on 74, and got 29.1 MPG.

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