New Legacy Owner has Questions about the Range Meter and MPG Accuracy

[MrChip]

Earlier today, I purchased my first Subaru - a 2024 Legacy Limited with 19,500 miles on it. I am thrilled to join the Subaru family. I absolutely love how the car drives, but I have a question about the accuracy of the MPG and range meter. When I purchased the car, the tank was full, and the display said it was averaging 18.7 mpg. I was a bit surprised by the low number, expecting something closer to 30. After driving it a little, I figured out how to reset the trip meter. After less than a minute, the mpg jumped to 27, and the range said 400. I then drove roughly 15 miles (mostly freeway). During this time, the MPG fluctuated between 27 and 31 while the range steadily decreased. Every couple of minutes, it dropped by 10 (390, then 380, then 370, then 360, then 350). After driving roughly 12 miles, my range dropped by 50 miles. The fuel gauge seemed to decrease a little bit from 3/4 to almost 5/8. I want to make sure there is nothing wrong with my car.

How accurate (or inaccurate) are the range meter and mpg? What variables/counters are affected when you reset the trip meter?

There are a few things of note that may be influencing my seemingly low fuel efficiency. First, the dealer I bought the car from replaced the battery a few weeks ago. The car had been driven less than 100 miles before I reset the trip meter. Is it possible that changing the battery made it lose all of its driving history, so it just needs me to drive it longer for the range meter to finish calibration and "stabilize"?

I was running the AC on maximum for my hour drive home from the dealer and the shorter 15-mile local drive. How much would this affect my mpg? Would it make a big difference if it were set to 68 degrees versus 60 degrees? I also had the start-stop system turned off.

Just for peace of mind, I am thinking about figuring out the mpg the old-fashioned way - top it off, drive for 200 miles, then see how much gas it needs to fill up. I would really appreciate any insight into this.

Thanks,
Chip

 

[bmart]

The onboard MPG meters are notoriously off by a lot and it varies by car. The only real calculation that will get you facts is to fill up at the same pump for a few tank fulls and do the math.

A/C on? A small difference driven more by driving habits, city/highway, elevation changes, and if you're a leadfoot or not.

 

[Alex_Rochester NY]

I wouldn't trust them very much, and I'd certainly stop watching that silly gauge and pay more attention to the road.

 

[Alex_Rochester NY]

The onboard MPG meters are notoriously off by a lot and it varies by car. The only real calculation that will get you facts is to fill up at the same pump for a few tank fulls and do the math.

A/C on? A small difference driven more by driving habits, city/highway, elevation changes, and if you're a leadfoot or not.

As a confirmed "lead-foot" myself, my Sport turbo get me about 17 mpg around town. Gets better on the highway, though....

 

[bmart]

Turbo: my average 21.5, track day 8.4 (~1.5 below readout in car)
N/A: my average 22.5, track day 12.25, towing 19

There are a lot of variables.

 

[SoobaRoobaDoo]

Nothing wrong with wanting a range display on occasion. I wouldn't watch the instantaneous MPG display since it changes continuously. The AVG MPG may be slightly more informative. Or may not.

Just for peace of mind, I am thinking about figuring out the mpg the old-fashioned way - top it off, drive for 200 miles, then see how much gas it needs to fill up. I would really appreciate any insight into this.

A single calculation relies on pumps shutting off at the same fill level. With just 200 miles, normal variation makes a big difference in MPG. A more accurate way is to calculate each fill for a while. Also divide the distance for 1 or 2 thousand miles by the gallons used. There will still be variation but you can see it.

We look at the AVG MPG display when we fill. It is reliably 1 to 1.5 MPG low. I can't tell you about the range display since this tank is so big that we just don't care.

 

[dentar99]

Not a legacy owner, but my forester consistently overrates fuel MPG by about 1.5 to 2. If it says 27, I'm really getting about 25, which is what I get when I track my fuel usage by hand.

Your best bet: Write down your odometer readings and the actual gallons purchased, and do the math like you live in the 1980s. It won't lie.

 

[MPK]

The onboard MPG meters are notoriously off by a lot and it varies by car. The only real calculation that will get you facts is to fill up at the same pump for a few tank fulls and do the math.

A/C on? A small difference driven more by driving habits, city/highway, elevation changes, and if you're a leadfoot or not.

The app Fuelio is a good app. It shows mpg after each fill-up.

 

[NEOHGuy]

Please don’t laugh too much at my response to the question. For years and for all my cars, I’ve kept a log of my car mileage, date of gas purchase, gallons, price per gallon, and total bill. Since I insist on topping it off every single time, I could manually calculate my mileage if I chose to do so. However, I don’t; I just record it. It’s just another reason why my wife calls me “Monk” (if you know why, you know).

By the way, the little journal book that you get from Subaru when you buy the car new facilitates that habit, as it fits nicely in the little pocket on the passenger side of a Legacy console. So every time I gas up, I grab the little book and away I go. For my 2020 Legacy at 15 miles new, I’ve got 80,000 miles on the clock today. Since I plan to sell the car this week, maybe I’ll have enough time to total up the numbers to see what kind of mileage I’ve gotten over the years.

Finally, I can’t really rely on the onboard mileage number as a few years ago the cumulative mileage readout crapped out and now says my total, overall average is 99.9. Nice but probably not accurate. Subaru said that as a telematic, they’d have to remove the screen. Don’t care that much to spend money on it.

 

[bmart]

like you live in the 1980s

In my head...I still do. Rock on, my brothers from other mothers.

 

[bmart]

For years and for all my cars, I’ve kept a log of my car mileage, date of gas purchase, gallons, price per gallon, and total bill.

Me too. You sound normal.

 

[chevy]

Not a legacy owner, but my forester consistently overrates fuel MPG by about 1.5 to 2. If it says 27, I'm really getting about 25, which is what I get when I track my fuel usage by hand.

Your best bet: Write down your odometer readings and the actual gallons purchased, and do the math like you live in the 1980s. It won't lie.

I have a '23 forester sport and found the mpg gauge to consistently read almost 2 mpg s high also..

 

[subbierf]

Legacy owner., 2023 formerly 2018 models. I can give some pretty decent stats on gas mileage. First of all ignore what they post on the car cuz it's complete BS even to this day. Pretty much Monday through Friday I drive pure City to work. It's about a 3 mi trip in the morning with not a lot of stops but on the way home lots of stop signs and red lights. Avery would top out at about 35 mph if that.Under these conditions I get 19 miles per gallon. Now add in some mixed driving after work around town with less stops and maybe moving 45 mph with maybe a bit of highway and shoot up the 22. If I take the car out purely on the highway for a trip maybe on a highway up to the mountains traveling at 65 to 75 no city at I have seen it as high as 29. I was hoping for a sweet spot where I could use it City during the week and take it out for some moderate trips on the weekend and end up with 25 mi to the gallon that seldom happens unless I've got one long trip where I'm cruising for maybe a half an hour each way at 50 mph or so. So pure City 19 mixed maybe 23 pure highway it does zoom up to about 28 to 30 depending on how fast you're going.