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2019 forester base
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Discussion Starter #1
LOW FUEL LIGHT.
I had one bar showing on the fuel gauge, with the computer saying there were 50 miles left in the tank. MPG showed I was getting 32mpg. The manual says low fuel light says it is supposed to come on when 2.5 gallons are left in the tank. Do the math...it does not make sense!
How many bars do you guys see on the fuel gauge when your low fuel light is coming on? Taking it to the dealership Monday.
 

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2019 Forester Touring CVT
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Low Fuel Light

LOW FUEL LIGHT.
I had one bar showing on the fuel gauge, with the computer saying there were 50 miles left in the tank. MPG showed I was getting 32mpg. The manual says low fuel light says it is supposed to come on when 2.5 gallons are left in the tank. Do the math...it does not make sense!
How many bars do you guys see on the fuel gauge when your low fuel light is coming on? Taking it to the dealership Monday.
I haven't had a chance to check mine yet but here's how I plan to do it.
When the 'Low Fuel' light comes on reset one of the trip computers to track how many miles are driven before you fill up.
Stated fuel tank capacity is 16.6 Gallons, note the gallons requited to fill the tank (this could vary with different stations and pumps based on their settings). Assuming you refueled at the moment the "Low Fuel" light came on, and assuming the On Board Computer was absolutely accurate in stating your MPG, then the gallons required to refill the tank should be 14.1.

The actual amount to refill the tank and miles remaining will vary for several reasons:
The On Board Computer is NOT absolutely accurate! (my On Board Computer appears to indicate nearly 2 MPG over actual MPG.
The Low Fuel Light may be calculated to illuminate based on current MPG, i.e. now driving in the city as opposed to highway.
Consider the miles driven since the Low Fuel Light illuminated, the gallons to fill the tank will be greater than 14.1 depending on how many miles were driven and at what MPG.

It's likely the engineers have looked at the worst case scenario and designed the system to display the warning earlier as opposed to later. It's a good idea to know how many more miles you can really travel after the Low Fuel Light illuminates.

I'll report back once I've had a chance to refuel after the Low Fuel warning illuminates.
 

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LOW FUEL LIGHT.
I had one bar showing on the fuel gauge, with the computer saying there were 50 miles left in the tank. MPG showed I was getting 32mpg. The manual says low fuel light says it is supposed to come on when 2.5 gallons are left in the tank. Do the math...it does not make sense!
How many bars do you guys see on the fuel gauge when your low fuel light is coming on? Taking it to the dealership Monday.
Twice now when my low fuel light came on I immediately filled the tank. Both times it took 14.1 Gallons. The low fuel light is deadly accurate no matter how far the computer thinks you can drive. Don't waste your dealers time.
 

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2019 Forester Sport
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Totally agree with @PearlWhite...I have the same experience so don't waste your time because the DTE says one thing and the FUEL LIGHT came on. When the light comes on, just get gas at the next opportunity you have or within 25 miles and you will be just fine. Nothing the dealer can do for you here.
 

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2019 ForesterTouring 2.5
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Just had the 100th refueling on the 2017 Touring and the average error between the Subaru calculated mpg and my hand calculation is +1.8 mpg optimistic i.e., the instrument panel is an average 1.8 mpg higher than actual. Hence the instrument panel range calculation is similarly optimistic, but since it rounds off to the nearest 10 miles, it pays to act conservatively and not push it.
 

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2020 Forester Touring CVT7
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LOW FUEL LIGHT.
I had one bar showing on the fuel gauge, with the computer saying there were 50 miles left in the tank. MPG showed I was getting 32mpg. The manual says low fuel light says it is supposed to come on when 2.5 gallons are left in the tank. Do the math...it does not make sense!
How many bars do you guys see on the fuel gauge when your low fuel light is coming on? Taking it to the dealership Monday.
for "miles left" its not using your total average , but the average in last ~1-5 miles(don't know exact number for forester) and it round down by 10 59.9mi will show as 50

59.9/2.5= ~23.96mpg in last 1-5mi

its only problem if it was other way and you end-up in the middle of the road with no gas...
 

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Discussion Starter #7
Totally agree with @PearlWhite...I have the same experience so don't waste your time because the DTE says one thing and the FUEL LIGHT came on. When the light comes on, just get gas at the next opportunity you have or within 25 miles and you will be just fine. Nothing the dealer can do for you here.
Did you get that I was down to 1/12 of a bar, and the low fuel light never came on?
Do the math, im sure 2.5 miles (triggers the low fuel light) x12 is far beyond the 16.5 gallons the forester is reported to hold. The light had not even come on yet, but I was too nervous to dive with only 1/12th the bar left.
 

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This may not be a popular response, but I totally disregard the low-fuel light.

I refuel when my fuel gauge hit 1/4 tank.

I guess that behavior comes from 50+ years of motorcycle riding...
 

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Today I drove till all of the bars disappeared. The low fuel light had been on since I hit apx. 40 miles to empty, My computer said I had about 20 miles to empty. I was able to stop withing a few miles and put in 15.2 gal. I guess this means that I still had about 1 1/2 gallons in the tank, but no way to know how much is usable unless I run it dry. That fill up, with all town driving got me 27.36 MPG. With almost 3,000 miles on the car, I'm very pleased.

I'm used to filling up at about 1/2 tank on my motorcycle and do the same with the car. No reason to think that the light and or computer are super accurate and I don't want to walk. No need for me to drive to an empty tank.
 

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Discussion Starter #10
Today I drove till all of the bars disappeared. The low fuel light had been on since I hit apx. 40 miles to empty, My computer said I had about 20 miles to empty. I was able to stop withing a few miles and put in 15.2 gal. I guess this means that I still had about 1 1/2 gallons in the tank, but no way to know how much is usable unless I run it dry. That fill up, with all town driving got me 27.36 MPG. With almost 3,000 miles on the car, I'm very pleased.

I'm used to filling up at about 1/2 tank on my motorcycle and do the same with the car. No reason to think that the light and or computer are super accurate and I don't want to walk. No need for me to drive to an empty tank.
Thanks for the post, Danornan. I am also at the same mileage you are. I am taking my car to the dealer tomorrow for a few other issues. I will ask if its normal for all bars to be gone until the light goes on. I had 1 bar left, computer showed 60 miles left, and NO fuel light. In fact, I have NEVER seen the fuel light since I got the car 3 months ago.
 

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Discussion Starter #11
Can someone with the 2019 let us know how many bars are showing on their digital fuel gauge when the low fuel light comes on? In my 2019 base, the light will not even come on with 1/12 bar left, which does not make much sense when considering the manual (and dealership) states that the low fuel light comes on when 2.5 gallons are remaining. Does the digital fuel gauge have to go to 0 bars before the light comes on?
Thanks for your help
 

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2019 Forester Sport CVT
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Can someone with the 2019 let us know how many bars are showing on their digital fuel gauge when the low fuel light comes on? In my 2019 base, the light will not even come on with 1/12 bar left, which does not make much sense when considering the manual (and dealership) states that the low fuel light comes on when 2.5 gallons are remaining. Does the digital fuel gauge have to go to 0 bars before the light comes on?
Thanks for your help
I’ve noticed mine, Sport model, come on with one bar remaining; 50 miles DTE on screen. (DTE does not include reserve fuel)
 

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What is reserve fuel? Are all the bars supposed to go away before the low fuel light comes on at which time you have 2.5 more gallons? I filled up with only one bar showing, with 60 miles showing remaining, and it only filled up with 12.6 gallons!
Im trying to see what other members in here have noticed when their low fuel light comes on.
 

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2019 Forester CVT w/paddle shifters
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Just had the 100th refueling on the 2017 Touring and the average error between the Subaru calculated mpg and my hand calculation is +1.8 mpg optimistic i.e., the instrument panel is an average 1.8 mpg higher than actual. Hence the instrument panel range calculation is similarly optimistic, but since it rounds off to the nearest 10 miles, it pays to act conservatively and not push it.
I've seen the same thing. Over the last 7 tankfuls my '19 Touring's real mpg is about 95% of the reported figure on the dash readout. It's a pretty consistent error each tank. My low fuel light comes on when the tank has around 2.5 gallons left and is usually showing one bar. One time I drove about 20 miles after the light came on and only took 14.6 gallons.

It's not cool that Subaru lies to its owners about mileage. They could program the display to accurately show your mpg. Do they show an optimistic number on purpose just so we'll fell better about our cars? Or did Subaru think that no one would check this?
 

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They know how many miles traveled and they know how much fuel is delivered to each injector. They can more accurately calculate millage. Mine always optimistically shows + 1 MPG. Explain why every vehicle errors on the optimistic side? It's rigged...
 

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I would love to know how any manufacturer can accurately display mileage. Please enlighten us. Details though, not wide assumptions on how easy it would be.
They know how many miles traveled and they know how much fuel is delivered to each injector. They can more accurately calculate millage. Mine always optimistically shows + 1 MPG. Explain why every vehicle errors on the optimistic side? It's rigged...
I reiterate.
 

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Discussion Starter #18
Today I was down to 1 bar, and the low fuel light came on after aprox 15 more miles driven. When I filled the tank, it took 13.5 gallons. So looks like the digital gauge has to be on 1 bar, then after the light you STILL have 2.5 gallons until empty. Do others in here have the same experience when your low fuel light comes on?
 

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Today I again drove until the low fuel light came on. For the record the low fuel light didn't come on until driving 5 additional miles after the fuel guage dropped to one bar. Vehicle said I had 50 more miles of range once the low fuel light came on. Stopped within 1 mile after light coming on and filled vehicle with 14.2 gallons. 2.4 gal left at a real by hand milage calculation of 25.1 and not the vehicle displayed milage of 27.4. Picture attached.

So at 25.1 MPG since last tank refill that would give a total tank range of 16.6 gal x 25.1 mpg = 416.66... Then divide 416 by 12 total bars gives about 35 miles per bar.

So hear I sit 5 miles into last bar with 2.4 Gallons left in the tank. Should have only 35 miles left at last bar but here I have 50 on display plus the 5 already driven for a total of 55 instead of the 35 per bar calculated above.

Close enough for me. I'm very pleased with both the fuel guage accuracy and the low warning. indicator. One bar left quickly followed by a low warning it's time to find gas IMO. No issues here.
 

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ScanGuage did it

I would love to know how any manufacturer can accurately display mileage. Please enlighten us. Details though, not wide assumptions on how easy it would be.
The simple answer is computers. The details? For modern engines to run at the needed stoichiometric ratio the engine computer needs to know precisely how much fuel and air is consumed. Gone are the days where fuel is metered through little holes in brass plugs! The precision required to properly meter the fuel is more than enough to accurately calculate your efficiency. The other needed measuring device, the odometer, is far less precise than the fuel metering system but even with a 2% error there it doesn't explain the 5-6% error people are seeing from their trip computers.

I installed a device called a Scangauge in my 2003 WRX. Once I got it calibrated for that particular car it was deadly accurate. When I got gas from the same pump at the same time of the day, it would always be within 0.1 gallon of what the Scanguage said. .1 gal. out of 14 ( my typical fill-up) is about a 0.7% error. And I'd bet most of that was due to the variation in the pump's auto shut off point. The thing was sensitive enough that I could tell when they switched over to winter gas from summer gas.

The accuracy of the pumps at gas stations are a far bigger source of error than the fuel metering system in our cars, but that wouldn't affect the car's real time mpg calculations. When refueling on road trips, almost all stations were within 2 or 3% of what the scangauge would report. Every once in awhile I'd get gas somewhere that was ripping people off, sometimes up to 10% overcharging. Funny, I never pumped less than the what scangauge reported.

If the company that makes the Scanguage, that works in any modern car, can do it then it should be no problem for a manufacturer to do it for each of their vehicles. It's only a matter of measuring two parameters and a little division.
 
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