3.8l Poor Gas Mileage

Boostpyro

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Hello all, new member and Genesis owner here as of a months ago. Quick Background: Im a long time Honda enthusiast and autocrosser. Been through many modified Integras but prior to recently getting married I traded in my AP2 S2000 for a more practical, yet fun, Genesis. Initially I wanted a BH V8/RSpec but they are rare down here. I found what I felt was a good deal locally, and more importantly gave me a great trade in value on my S2000 (over private party) and I got my 2015 3.8 Empire State Genesis w/74k miles for $19.5k. It was in such great condition I thought it was worth saving a few thousand vs getting a lower mileage version. They also just did an oil change, brake fluid, air filter, front brakes/rotors and brand new tires.

After driving for awhile, I love the car. No problems at all and everything works great. With that said, I'm saddened by the V8-like mileage. My first couple weeks I was averaging 22MPG each tank around town/city with little hwy driving. Not too bad I thought considering its rated at 18city. 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...

Also, ive noticed after a fill up, the range says 480 miles for the tank...last time I filled up I only made it 376 miles with a light foot with mixed driving. And Ive noticed that the average MPG estimated by the car is about 1mpg lower than actual based on calculating the tripometer miles vs how many gallons filled up math. So annoying!

Any ideas or similar problems?
 

BenGenesis

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

Boostpyro

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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.
 

JT@rvsusa

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Hi guys, also new here. I'm not a vendor yet and don't know if we'll do it in the future but figured I'd share since we have a 2015 Genesis 5.0 and mpg came up. We've been testing our RVS Technology product in my father's car and now I have some data post treatments. I drive the car about once a week from West Palm Beach to Miami, about 65 miles each way. Traffic is pretty varied, from 80mph to stop and go. Before treatments I got best avg mpg of 24.8-25.5. This past tuesday took another trip and to my amazement got 30.3 mpg. I pretty much set the active cruise to 75 mph and let the car do it's thing. A V8 with 420hp and 30 mpg, not bad!

Boostpyro, have you done any fuel injection treatment? Checked plugs? With 75k miles it could already have some pollution and wear.18907
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Boostpyro

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Hey JT. I haven't don't any fuel injector cleaning or changed the spark plugs. Doesnt seem like theres to much out there on the spark plug replacement for the except on the BH 3.8l's but I guess they should be about the same as my DH. Apparently you have to take off the intake plenum to get access to the spark plugs but I havent looked into it enough. Im also not sure fuel injector cleaner is recommended on the Genesis.

Regarding you mileage, that's some really good numbers for the V8.... better than my V6. One thing I noticed is the range shows you still have 377 miles left, so Id be interested to see what you ended the tank with as its always easy to get some crazy high numbers early into a tank depending on hills, drafting, coasting.
 

TurtleBoy

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JT@rvsusa

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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.
Exactly, way too high. Usually the recommended pressure plus 2-3 psi is the best for wear and economy. For example Costco now fills +4 psi at their tire centers if the tires are non oe equipped and used.
 

Boostpyro

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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.
It is a max, but while trying to maximize as much fuel mileage as possible, I wanted to take tire pressure out of the equation. To me I feel the tires specific rating is most important as the base, not the cars recommendation which is based generally on OE tires (which were recalled lol) BUT in the end, having it at the max would only help the mileage, which is my point in the thread. I’m not keeping it at that pressure, just trying to get a “best case scenario” mileage, which was still bad.
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TurtleBoy

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Boostpyro

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Your previous post made it sound like that was what you were running at all of the time which would not be a good thing.
I guess it did sound like that :unsure: In my first post I was talking about my drive home from Florida (which was just a week ago). Before I left I moved the pressures up to that point to see if that had any affect on it since it would be 95% HWY on the way home. In the end it didn't seem to have any at all.

Guess I should look into spark plugs maybe since its getting up there in mileage. It appears the driver side plugs are the real hassle :confused:
 

TurtleBoy

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Boostpyro

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I think you are trying to achieve something that may not be possible. Many factors go into the difference between EPA mileage and actual mileage. Just enjoy the car and not worry about trying to get to a standard that is meaningless in the real world. :cheers:
That’s perfect advice. It may not be achievable, I’m just wanting to make sure things are square and safe before I start having fun :sneaky:

With that said, how do I do a V8 swap? Lol jk. I actually like the V6 a lot. Just wish there was more readily available room for improvement.
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EdP

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That’s perfect advice. It may not be achievable, I’m just wanting to make sure things are square and safe before I start having fun :sneaky:

With that said, how do I do a V8 swap? Lol jk. I actually like the V6 a lot. Just wish there was more readily available room for improvement.
Your mileage is about the same I've gotten on two different 3.8 Genesis. It is a much heavier car that you previous ones and it takes more energy to get it up to speed. As for ECO mode, it helps around town but does nothing on the highway. If you are cruising at highway speed and are in top gear, that is as good as it gets. What it does do, at lower speeds it lowers the shift points and softens the pedal so you cannot accelerate too fast. \

Doubt that changing plugs will make much difference, they should last another 25k miles or so.
Also, 50 psi is too high. 38 to 40 is good.

I've never seen a car get near the EPA rating so I was not disappointed at all.

Oh, you mentioned leaving Florida. If you spend time in a cold climate, short trips is a killer for fuel economy. A 2 mile trip to the store in freezing weather may get you 12 mpg.
 

Kon

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Is your car AWD? Mine is AWD and I get roughly the same MPG, which I agree is pretty terrible.

Also, 50 PSI is crazy... I'm surprised you didn't have a blowout at that pressure. I thought mine was high at 38!
 

Boostpyro

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Is your car AWD? Mine is AWD and I get roughly the same MPG, which I agree is pretty terrible.

Also, 50 PSI is crazy... I'm surprised you didn't have a blowout at that pressure. I thought mine was high at 38!
Mine is RWD, otherwise I wouldn't be complaining. Also the PSI doesn't worry me for testing. The max rating is simply a max that is safe to drive. I understand its not the best compromise of comfort/performance but it doesn't hurt for testing.
Your mileage is about the same I've gotten on two different 3.8 Genesis. It is a much heavier car that you previous ones and it takes more energy to get it up to speed. As for ECO mode, it helps around town but does nothing on the highway. If you are cruising at highway speed and are in top gear, that is as good as it gets. What it does do, at lower speeds it lowers the shift points and softens the pedal so you cannot accelerate too fast. \

Doubt that changing plugs will make much difference, they should last another 25k miles or so.
Also, 50 psi is too high. 38 to 40 is good.

I've never seen a car get near the EPA rating so I was not disappointed at all.

Oh, you mentioned leaving Florida. If you spend time in a cold climate, short trips is a killer for fuel economy. A 2 mile trip to the store in freezing weather may get you 12 mpg.
I figured ECO was pretty useless, but wasn't sure. I definitely can't justify even more sluggish acceleration for slightly less fuel consumption though. ....that Sprint Booster is really calling my name. Its been really hard to get use to DBW throttle.
 

Boostpyro

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wonder how many people actually do this out there
I'm definitely the only one. They actually put the max load rating on tires specifically for me alone. Nothing more dangerous than testing fuel mileage within the tire's spec!
 
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Kon

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I'm definitely the only one. They actually put the max load rating tires specifically for me alone. Nothing more dangerous than testing fuel mileage within the tire's spec!
The miniscule gain in MPG (if there's any gain at all) will be far outweighed by the increased wear on your tires, not to mention the terrible ride quality.
 

Boostpyro

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The miniscule gain in MPG (if there's any gain at all) will be far outweighed by the increased wear on your tires, not to mention the terrible ride quality.
As mentioned before I simply wanted to take it out of the equation. This isn't a normal practice, cripes.

Also, its worth mentioning, that rating is based on cold pressures. The max a tire is designed to handle safely. I under filled to be sure the heated pressure wasn't above the max cold pressure. Therefore, no harm, no foul.

Appreciate your help with my questions though!
 
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