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At exactly 1/2 tank i can put 9 gallons of fuel in the car. I found that odd since we dont have 18 gallon tanks
4 bars isn't half a tank. It's 56% used which equates to about 15.7 total gallons which is the reported Max by forum members despite 15.3 in the manual
 

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Discussion Starter · #43 ·
It is possible that the 2020’s have this issue “improved”.
 

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It is possible that the 2020’s have this issue “improved”.
Hahah AlfaCrisis I can assure you it's got exactly the same issue.

After some fairly diligent experimentation I have some interesting findings. There are many data points here but I think there are a few crucial factors at play. We can all agree that the stated capacity of the fuel tank is larger than FCA officially states. The main reason I assert this is because the range does indeed fluctuate in correlation with my average fuel economy displayed in the driving data. I just filled up tonight, I was averaging 24.4 mpg at fill up and I got 392 miles of range displayed. If you divide that estimated range at full whether its in the 380s or 390s by 15.3, the mpg I would need to get that range is higher than what's on the computer by a few percent.

I think the tank capacity that the computer uses to calculate estimated range at full is around 16 gallons. 24.4mpg x 16 gallons = 390.4 miles. I will monitor this at every fill up and check the multiplier each time.

Second thing that threw me off recently was when I filled up two days ago only 3.57 gallons I went from one red bar and 16 miles of range up to 207 miles of range and 4 bars, after adding 3.5 GALLONS!! I was averaging 24.7 miles at the time of that small fill, and I had 283 miles racked up on that tank. 287 mi / 24.7 mpg = 11.62 gal.
If we assume 16 gallons to be the full tank, then I had 4.38 gallons remaining but the computer thinks I only had (16/24.7) 0.65 gallons remaining.

When I added 3.57 gallons to my estimated 4.38 gallons remaining then I would have had an estimated total of 7.95 gallons. This sounds about right as at that point the computer thought I had 8.38 gallons of fuel (207mi/24.7mpg). I continued to drive it and the range dropped exactly as expected as if I had about 8 gallons at that fill up.

I did not reset the trip computer at that point and racked up another 56 miles bringing my total to 343 miles when I filled up tonight. I was only able to put in exactly 10.3 gallons exactly. If we, again, assume that the tank is 16 gallons then I had 5.7 gallons at the time of fill-up. Assuming about 8 gallons at the last partial fill up, it is entirely possible to believe that I drove 56 miles using 2.35 gallons, which would come out to 23.8mpg, which is almost perfect because my average dropped from 24.7 to 24.4 over those 56 miles.

The data and subsequent calculations reveal a pretty good case for a 16 gallon tank, now it would be a matter of taking very precise notes and running experiments like this over and over again.

One thing is extremely clear however and that is the precipitous drop in range that the computer shows towards the end of the tank when in reality the estimated range at full seems to me to be very largely accurate. Why Alfa Romeo insisted on programming it this way is infuriating. What good is it for range to be accurate at the beginning of the tank and to be utterly useless at the end of the tank?!?
 

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Discussion Starter · #45 ·
Hahah AlfaCrisis I can assure you it's got exactly the same issue.

After some fairly diligent experimentation I have some interesting findings. There are many data points here but I think there are a few crucial factors at play. We can all agree that the stated capacity of the fuel tank is larger than FCA officially states. The main reason I assert this is because the range does indeed fluctuate in correlation with my average fuel economy displayed in the driving data. I just filled up tonight, I was averaging 24.4 mpg at fill up and I got 392 miles of range displayed. If you divide that estimated range at full whether its in the 380s or 390s by 15.3, the mpg I would need to get that range is higher than what's on the computer by a few percent.

I think the tank capacity that the computer uses to calculate estimated range at full is around 16 gallons. 24.4mpg x 16 gallons = 390.4 miles. I will monitor this at every fill up and check the multiplier each time.

Second thing that threw me off recently was when I filled up two days ago only 3.57 gallons I went from one red bar and 16 miles of range up to 207 miles of range and 4 bars, after adding 3.5 GALLONS!! I was averaging 24.7 miles at the time of that small fill, and I had 283 miles racked up on that tank. 287 mi / 24.7 mpg = 11.62 gal.
If we assume 16 gallons to be the full tank, then I had 4.38 gallons remaining but the computer thinks I only had (16/24.7) 0.65 gallons remaining.

When I added 3.57 gallons to my estimated 4.38 gallons remaining then I would have had an estimated total of 7.95 gallons. This sounds about right as at that point the computer thought I had 8.38 gallons of fuel (207mi/24.7mpg). I continued to drive it and the range dropped exactly as expected as if I had about 8 gallons at that fill up.

I did not reset the trip computer at that point and racked up another 56 miles bringing my total to 343 miles when I filled up tonight. I was only able to put in exactly 10.3 gallons exactly. If we, again, assume that the tank is 16 gallons then I had 5.7 gallons at the time of fill-up. Assuming about 8 gallons at the last partial fill up, it is entirely possible to believe that I drove 56 miles using 2.35 gallons, which would come out to 23.8mpg, which is almost perfect because my average dropped from 24.7 to 24.4 over those 56 miles.

The data and subsequent calculations reveal a pretty good case for a 16 gallon tank, now it would be a matter of taking very precise notes and running experiments like this over and over again.

One thing is extremely clear however and that is the precipitous drop in range that the computer shows towards the end of the tank when in reality the estimated range at full seems to me to be very largely accurate. Why Alfa Romeo insisted on programming it this way is infuriating. What good is it for range to be accurate at the beginning of the tank and to be utterly useless at the end of the tank?!?
Interesting theory, but perhaps blown out of the water by a couple of early owners who ran dry and reported 15.3 gallons to then fill up.
 

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I conclude after reading this thread that the gauge is an indication of level, and that the tank is not uniform in shape, thus the gauge is a poor indicator of the volume of gas left in the tank
 

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Discussion Starter · #49 ·
I have a Ti (14.5 gallons) plus the filler pipe do QV's have larger tanks
All Giulia’s have the same tank...at least 17-19...never heard if the 20+ tank size changed.
 
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I conclude after reading this thread that the gauge is an indication of level, and that the tank is not uniform in shape, thus the gauge is a poor indicator of the volume of gas left in the tank
Agreed. But how do you explain a car screaming at me to pull over and get gas when I really had almost 4.5 gallons left in the tank? That seems like an overly dramatic temper tantrum in typical Italian fashion.
 

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Agreed. But how do you explain a car screaming at me to pull over and get gas when I really had almost 4.5 gallons left in the tank? That seems like an overly dramatic temper tantrum in typical Italian fashion.
Maybe Italian engineers saw the map of the US and imagined that our gas stations are a long way apart ;)
 

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The main reason I assert this is because the range does indeed fluctuate in correlation with my average fuel economy displayed in the driving data.
...
What good is it for range to be accurate at the beginning of the tank and to be utterly useless at the end of the tank?!?
In my experience, the estimated range has no direct correlation with the indicated average fuel economy since last reset. It is more directly related to the "fuel efficiency in the last 20 minutes" as shown on the gauge cluster when you're in Normal mode. I say this because I can fill up with or without resetting the average fuel economy and get a range estimate (let's say it's 380 miles). If I put the car into RACE mode and drive a few miles, the range will come down significantly (let's say 300 miles). Then, if I go back to Normal, it'll slowly climb back up until it gets to (or even exceeds) 380 miles, depending on how the new "20-minute average" compares. In that time, since the sample size on mileage is small if I haven't re-set the computer, the indicated average doesn't change at all.

Therefore, I don't agree with the "the range is accurate at the beginning and utterly useless at the end." I have found that it's a bit conservative in Normal mode, pretty accurate in Dynamic unless you're on surface streets driving spiritedly, and downright optimistic in RACE mode. I just drive until I get the warning light and then assume I've got about 2 gallons (25 miles in D or RACE, 50 miles in A or N).
 

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In my experience, the estimated range has no direct correlation with the indicated average fuel economy since last reset. It is more directly related to the "fuel efficiency in the last 20 minutes" as shown on the gauge cluster when you're in Normal mode. I say this because I can fill up with or without resetting the average fuel economy and get a range estimate (let's say it's 380 miles). If I put the car into RACE mode and drive a few miles, the range will come down significantly (let's say 300 miles). Then, if I go back to Normal, it'll slowly climb back up until it gets to (or even exceeds) 380 miles, depending on how the new "20-minute average" compares. In that time, since the sample size on mileage is small if I haven't re-set the computer, the indicated average doesn't change at all.

Therefore, I don't agree with the "the range is accurate at the beginning and utterly useless at the end." I have found that it's a bit conservative in Normal mode, pretty accurate in Dynamic unless you're on surface streets driving spiritedly, and downright optimistic in RACE mode. I just drive until I get the warning light and then assume I've got about 2 gallons (25 miles in D or RACE, 50 miles in A or N).
Hmm that's interesting... I would say in my experience with my driving cycles I am very regularly getting between 23.5-24.5 mpg and it really doesn't change except by a few tenths of a mpg over the entire life of the tank (unless I go for a Sunday romp). It would be very easy for me to confound the "20 minute" mpg with the mpg displayed in the trip computer at any point filling up. In the scenario I described earlier I feel very confident saying that when it showed 16 miles of range and one angry red bar I still had well over 4 gallons still in the tank. As for the rest, I guess it's hard to say. Seems like everyone has equally as confounding experiences and that makes me question the efficacy of the programming for all information regarding fuel consumption/remaining fuel level. I guess we've all been prudent enough not to get caught with our pants down or our tanks empty yet;)
 

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I have done a different experiment: run the fuel down low, then add a small amount of fuel, read the gauge, add another small amount of fuel, read the gauge etc. I have done this from various fuel level starting points. My conclusion: the gauge has about 2 gallons of hysteresis, probably to avoid the reading from changing under acceleration. It may be more complex than simply hysteresis. However, I believe this clearly explains the "small fill" issue described above.

Also, I suspect that "full" as defined by the EPA is 15.3 gallons, but that more fuel can be forced in at the risk of damaging the evaporative emission control system.

I am not 100% certain, but if the reserve is assumed to be above the F mark, each mark is assumed to mean less than the corresponding fraction (7 bars means between 3/4 and 7/8 tank-reserve) and one is careful to avoid situations where the hysteresis causes non-sense readings (i.e. adding a couple of gallons) the gauge is pretty linear.
 

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Hmm that's interesting... I would say in my experience with my driving cycles I am very regularly getting between 23.5-24.5 mpg and it really doesn't change except by a few tenths of a mpg over the entire life of the tank (unless I go for a Sunday romp). It would be very easy for me to confound the "20 minute" mpg with the mpg displayed in the trip computer at any point filling up. In the scenario I described earlier I feel very confident saying that when it showed 16 miles of range and one angry red bar I still had well over 4 gallons still in the tank. As for the rest, I guess it's hard to say. Seems like everyone has equally as confounding experiences and that makes me question the efficacy of the programming for all information regarding fuel consumption/remaining fuel level. I guess we've all been prudent enough not to get caught with our pants down or our tanks empty yet;)
I would say the vast majority of my tanks are around 20 or 21 MPG (calculated at the tank, not indicated) because I use a lot of surface streets and live in a traffic-heavy metro area. However, if I'm on a road trip and drive an entire tank on the highway, I've seen as high as 28MPG (on the flip side, I've seen as low as 15MPG on a fun Sunday drive).

It's certainly plausible that there's 4 gallons left when the range reads '---' but the most infuriating thing to me is the inconsistency. I've had range go to '---' with more than a quarter tank shown a few times but I've also seen it show an estimate range until the gauge turns red and then showing '---' at least once. It really does seem related to the driving mode an the recent economy.
 

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I believe that the same person engineered the fuel level system, the oil level system (2.0's) and the TPMS. They are all very poorly done in comparison to other cars. But that's the Yin and Yang of life with an Alfa. Always was, is, and may well be, in the future.
 

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Guys, has anyone from you got similar issue to mine? Yesterday when I had 1 fuel bar I checked in 'CarScanner'app and it shows 5.22l (1.37gallons), when I refilled my tank it added maximum 47l (12.41 gallons). There was some gap around 5-6l (1.32 - 1.58 gallons).
 

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Why can't I half ass anything :rolleyes: I already keep a spreadsheet to keep track of my fill ups, but I've now added more data points to try and track how accurate all of the programming/metering is. I'm not concerned about fuel bars at all since they're fairly meaningless.

The "potential range" at any point is the trip odometer since last fill up added to the estimated remaining range. I was pleasantly surprised that upon filling that tank and resetting the trip odometer that it estimated 318 miles of range compared to my calculated potential range of 320.6 miles at my current indicated MPG of 19.5. My actual calculated MPG 139.6mi/7.303 gallons of fuel revealed that the computers 19.5 MPG estimate was off, and it was right around 19.1 MPG.

The calculated tank size is just a function of MPG displayed at time of fill up and estimated range after the car was filled up to the first click (yes, on the same pump almost every single time). The experiment here is to see if that calculated tank size fluctuates, by how much, and in correlation to what.

Let me fill up the car at least four more times at different points in the life of the tank and I'll report back the results. Nothing like some good hard data!
 

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A few days ago I filled up at 2.7% fuel level (OBD readout) and the pump stopped at 55.9 liters (14.7 gal).

At this point there were no bars showing on the fuel level meter.
At ? 5% ? there was one red bar showing.
 

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A few days ago I filled up at 2.7% fuel level (OBD readout) and the pump stopped at 55.9 liters (14.7 gal).

At this point there were no bars showing on the fuel level meter.
At ? 5% ? there was one red bar showing.
Wow it was quite accurate for you only 0.5l difference. Which app are you using, torque or something else? I have MES and I remember that fuel level readings captured from OBD have been different than on torque/car scanner app. Recently I have been using Car scanner which is more interesting than Torque and more convenient than MES itself.
I'm still wondering why obd shows 5.22l which corresponds to 2 bars according first post evaluation and I refilled with 47l of fuel so gas pump has clicked that it was full. According obd it should add -- 52l - 53l...
 
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