Slumping fuel economy

[smashweights]

Ove the last 6 months I've been noticing a consistent drop in MPG across the board. My commute around town used to be around 17mpg now I'm getting 15. My 800 mile road trips would average 22-23 mpg and the last two have been 19-20 mpg. What gives? Running the same 87 octane, seems to have started when I got my last oil change about 5k miles ago. Anything else this could be especially that's fixable?

 

[Scap]

Winter fuel could explain it if you weren't saying 6 months...

 

[MurphBigHorn]

Funny last two tanks. Same kinda driving. I have dropped 3mpg both tanks. It’s not a daily so doesn’t bother me. However. I need to add 5psi to each tire since the temps have dropped. And haven’t. I cracked it up to that.

 

[kapinallinen2]

Winter blend most likely.

 

[PM-Performance]

I have been swearing up and down since the great gas hikes of Covid, that we have been getting the “winter blend” all year long now and at a stupid jacked up price.
My truck has also lost a consistent 2mpg all else being the same over the last year or 2.
I just dumped ethanol free in it and guess what….. same issue. Pretty sure that is a scam too.

 

[smashweights]

Winter blend most likely.

Started 6 months ago, I was hoping it was a fluke

 

[Dewey]

I get my best mpg in the heat of the summer and steadily drops with the temps. Usually 3 mpg difference in the coldest period of winter. Nothing unusual and the same with every vehicle I ever owned.

 

[RamGuy32]

Double whammy...winter blends with lower BTU content, and colder air is much thicker requiring more energy to push these non-aerodynamic vehicles through it. Best mileage you'll ever get is sea level or lower through an Arizona desert in the summer.

 

[smashweights]

Again, this started in the summer and has remained consistent since then. The previous trips mpg were the same time of year. I live at 20 feet above sea level on the Gulf Coast.

 

[Scram1500]

Ove the last 6 months I've been noticing a consistent drop in MPG across the board. My commute around town used to be around 17mpg now I'm getting 15. My 800 mile road trips would average 22-23 mpg and the last two have been 19-20 mpg. What gives? Running the same 87 octane, seems to have started when I got my last oil change about 5k miles ago. Anything else this could be especially that's fixable?

What oil was used? Also take a look at the air filter and wear pattern on your tires. Alignment might be out

 

[2021EcoDiesel]

Alignment, tire pressure, brakes dragging, wheel bearing failing, differential oil breaking down, dirty air filter, dirty fuel injectors, blocked fuel filter. A whole lot of things could be causing it, and I don't want to insult anyone's intelligence. But, maybe put the truck on jackstands and make sure none of the wheels are dragging a little extra than normal.

If you're pretty sure it happened around your last oil change, I'd make sure it's not filled with a heavier weight oil, or overfilled with oil, that could possibly knock a mile or two off highway MPG. I'd imagine you might have a dirty fuel injector or something though. That seems more likely to me.

 

[6of36]

4 to 5 years old, you may need a tune up too, besides fuel and air filters, or a dirty set of injectors. Plus the winter blend of late. When I picked up my truck in September, the first tank I got 20.5 MPG. I just drove 400 highway miles last week and got less than 17. I was driving faster though.

 

[smashweights]

What oil was used? Also take a look at the air filter and wear pattern on your tires. Alignment might be out

Should have been 0w20 full synthetic, had alignment done at that change too.

Alignment, tire pressure, brakes dragging, wheel bearing failing, differential oil breaking down, dirty air filter, dirty fuel injectors, blocked fuel filter. A whole lot of things could be causing it, and I don't want to insult anyone's intelligence. But, maybe put the truck on jackstands and make sure none of the wheels are dragging a little extra than normal.

If you're pretty sure it happened around your last oil change, I'd make sure it's not filled with a heavier weight oil, or overfilled with oil, that could possibly knock a mile or two off highway MPG. I'd imagine you might have a dirty fuel injector or something though. That seems more likely to me.

Air filter was just changed a few months before this, alignment done around that time too, I'm neurotic about tire pressures and run 38 front 36 rear on stock size. How would one diagnose or treat dirty injectors, diff oil, fuel filter?

4 to 5 years old, you may need a tune up too, besides fuel and air filters, or a dirty set of injectors. Plus the winter blend of late. When I picked up my truck in September, the first tank I got 20.5 MPG. I just drove 400 highway miles last week and got less than 17. I was driving faster though.

Pardon my ignorance but what kind of tune up?

 

[Scram1500]

Should have been 0w20 full synthetic, had alignment done at that change too.

It's possible they gave you a thicker oil or bunged up the alignment, or both

 

[BowDown]

Winter blend fuel causing decreased MPG is a myth, winter blend only has butane added. The loss of mpg (and increase in performance) is due to cooler temps and the IAT/MAF/MAP adjusting the fuel tables due to the increased air the engine is ingesting. Colder temps = more dense air = more fuel added to the combustion process to maintain the desired A/F Ratio

The Difference Between Winter- and Summer-Blend Gas - AMSOIL Blog

Summer-blend gas provides about 1.7 percent increased energy content, meaning it offers a slight boost in fuel economy. Here's how else it's different.

blog.amsoil.com

How winter weather affects your fuel economy | Shell Australia

Here's how cold weather makes your car use more fuel – and what you can do to minimise the loss.

www.shell.com.au

How to Get the Best Gas Mileage in Winter - AMSOIL Blog

You've probably noticed gas mileage drops in winter. Here's what's going on and how you can get the best gas mileage in winter.

blog.amsoil.com

Ergo, your fuel mileage is dropping because the temps are dropping; I go from ~17.5 city down to ~16.5 when air temps are 60° or lower over a prolonged period.

 

[BowDown]

Should have been 0w20 full synthetic, had alignment done at that change too.


Air filter was just changed a few months before this, alignment done around that time too, I'm neurotic about tire pressures and run 38 front 36 rear on stock size. How would one diagnose or treat dirty injectors, diff oil, fuel filter?

Pardon my ignorance but what kind of tune up?

The kind where you pay out a crap load of money for them to change your plugs (for no reason), give you an overpriced air filter and a pat on the head as you leave. Modern engines rarely need a tune up beyond plugs ( only at >100,000 miles) and an air filter.

 

[yankeefan31569]

my fuel
mileage
went sour also around 70k 2019 CC BH NON E -HEMI - guy at Napa store
told me to replace the spark plugs.
maybe give that a shot my buddy said he will do it in my driveway for $100 see if that helps..

 

[BowDown]

my fuel
mileage
went sour also around 70k 2019 CC BH NON E -HEMI - guy at Napa store
told me to replace the spark plugs.
maybe give that a shot my buddy said he will do it in my driveway for $100 see if that helps..

Waste of money, your plugs are fine with just 70K on them. I'm at 67K miles

 

[PM-Performance]

my fuel
mileage
went sour also around 70k 2019 CC BH NON E -HEMI - guy at Napa store
told me to replace the spark plugs.
maybe give that a shot my buddy said he will do it in my driveway for $100 see if that helps..

****…. If the guy at the local Napa store said so, might as well do it lol

 

[smashweights]

Man, there has to be something with the fueling going on here. Highway economy has been steadily dropping for the last 1-2 years. Used to get 22, then 20, then 19 now this?? Daily driving economy had plopped from 16-17 down to 14-15 too. I drive like a grandpa and I notice the ECO light seems to come on less and the truck seems to downshift more on sight uphills. Can there be a dirty sensor? Something clogged? Something needs reset? Is this what happens as the ET battery ages? Just drove 12 hours round trip along the Gulf Coast, no traffic, 75 mph with adaptive cruise, same 87 Shell gas, just like every other drive I've had and the highway mpg just continues to trend down. Just turned 50k on the odometer. This is 100% highway miles and pretty representative of the entire 850 mile trip...