Losing gas really quickly?

fjrman

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Still don't know the definition of "current fuel economy".

It's not instantaneous so it must be an average over some period of time.

Honda's definition changed from 2016 to 2017.

From my 2016 Operator's Manual -- the distance(range) is estimated from the fuel economy of your previous trips.

From the 2017 Manual -- the distance is based on the vehicle's current fuel economy.
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frontlinegeek

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Still don't know the definition of "current fuel economy".
It is known and is the same in almost any car that has it. It is the actual live consumption based on the known quantities of fuel used when an injector fires. The only real variation will be from older worn out or gummed up injectors or if your fuel pump is not providing the right pressure.

It's not instantaneous so it must be an average over some period of time.
There is nothing to be gained from an instantaneous update on the average. The gauge that shows the live economy is the only thing that matters in the moment. The average shows if you are able to be consistent over time. The amount of memory and CPU time needed to calculate based on storing literally every single seconds worth of live data is large for a system that is engineered down to the least possible cost. It is exceedingly likely that it is using a 10s of seconds sample rate for the average calculation. For how we use these vehicles, it is MORE than accurate enough.

Honda's definition changed from 2016 to 2017.
Could easily be down to a mistake in either years manual. Regardless of the initial calculation, the rolling recalculation is done off the rolling average economy. This is why the estimated range will go down as you start to use it and initially, not at a rate that matches the trip counter.

I think at this point, I am approaching unhelpful levels of frustration with people that refuse to read both what is in the manual and what I have pointed out. To the OP and the other poster with what certainly could be issues, I hope you figure them out. I have to abandon this thread.

Honda Civic 10th gen Losing gas really quickly? Civic fuel range page
 

fiend busa

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The estimated range until empty is simply a math equation your car is constantly doing. The equation accounts for more variables than I'm showing here, but the basics of it is: Current fuel level * MPG = Miles until empty

If you fill up and get on the expressway for 10 miles, you'll have 40-50mpg. As soon as you get off and start city driving, that will plummet down very quickly. If you have a high average MPG, your miles until empty will be high also. I've also found that when you get the warning for low fuel, you have 2 gallons left in the tank.
Yeah can confirm

Usually I get a low fuel warning at 40km - after resetting the battery, I got it at 100km since my MPG was shit.
 

Gruber

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Still don't know the definition of "current fuel economy".

It's not instantaneous so it must be an average over some period of time.

Honda's definition changed from 2016 to 2017.

From my 2016 Operator's Manual -- the distance(range) is estimated from the fuel economy of your previous trips.

From the 2017 Manual -- the distance is based on the vehicle's current fuel economy.
My newer manual (2018 that came with the car and the revised next version after) still mentions previous trips for figuring the range, so I don't think it changed. The range after refueling can only be a prediction or a rough estimate no matter how it's calculated.

The gas mileage whether given by the car computer or measured for one tankful or less based on pump readings, can't possibly be more accurate than several percent. Several percent can easily be 1 mpg or more for each, so the error on the "measured" difference between the two can be huge. Like 100% or more.

The computed range is even less accurate because the amount of gas left in the tank is a separate measurement, which again is not more accurate than several percent at best. The temperature and density of the fuel may change significantly just after refueling.

The most accurate measurement would be based on pump readings, but over long mileage and many tanks. The longer the mileage the closer to actual gas consumption. My car shows me 30.6 mpg over more than 3500 miles. Only if I also had measured the pump mileage over this distance, could I figure the error of the computer that I could actually believe. But I hadn't.
 
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Gruber

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Just happens that my daughter recently drove a rental 2019 Chevy Malibu for several days less than a month ago. This was the top Premier trim with a 2.0T 250 hp engine and a lot of features. When I asked her how she liked that car, she said it's fine, but the fuel range behaves strangely and fluctuates up and down.

While theoretically the fuel gauge in a Chevy (or even Honda??? :fear:) can be broken or malfunction, I assumed she just was not familiar with the computed fuel range. Some cars might have more "conservative" algorithms that filter out "unexpected" results or average over longer periods.
 


Daniel644

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The engines are engineered and the fuel injection volumes are a known quantity. This is not voodoo as not knowing would mean not having the right fuel/air mixture and your car would run like crap. The computer is tracking every single fuel pulse that is injected and that, in lockstep with how far you have driven, will let it calculate your current fuel efficiency. The only guesswork is when trying to guess your current range remaining due to variations in the reading from the fuel level float in the tank. This is also why doing calcs yourself are unpredictable as even half a gallon/2 liters of incorrect measurement will cause as much as a 5% swing in what the car thought you had for range.

Also, our cars definitely do track everything that is injected. If you idle your car or use autostart, your economy ratings will look like garbage.
It can measure the length of the pulse of the injector being open then from that estimate the amount of fuel that should be flowing through the injector based on the stock fuel pressure the vehicle was designed to run at, it can't measure the actual flow of fuel through the injector. This is a common misconception, it then also measures via the O2 sensors the amount of unburned fuel that makes it to the exhaust, that measurement is what s used to lean or richen the fuel air mixture, not a measurement of the flow of fuel through the injector. all of these variables eventually get out of spec as crud builds up in the fuel system and injectors get clogged and that kind of stuff.

ultimately these fuel mileage systems are just a really really well educated guess of the fuel mileage based on known details of the system as a whole. And your MPG goes down when you idle because the engine IS burning fuel since it's running so it still has those injector pulsing being known. Their is no sensor on any car measuring the exact amount of fuel actually flowing through the injectors.

The most accurate measurement would be based on pump readings, but over long mileage and many tanks. The longer the mileage the closer to actual gas consumption. My car shows me 30.6 mpg over more than 3500 miles. Only if I also had measured the pump mileage over this distance, could I figure the error of the computer that I could actually believe. But I hadn't.
Ideally using the same pump each time at the same time of day in the same weather conditions due to the fact that different pumps have shutoff points and there is some level of density related to temperature. The ideal configuration is actually the way the Mythbusters did their MPG testing, where they weighed the exact amount of fuel they used over a set distance (like they did in the "Golf Ball Dimple Car" Episode).
 
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tacthecat

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Two points:
1) Own 2 Civics ('98 Ex - 170,000 miles & '12 Si - 90,000 miles) regularly run both to the Lo-Fuel light or alert turns on - never have had an issue with the fuel pump and have never heard of a 7th - 10th Civic having a fuel pump overheating issue related to low fuel level.
2) On our '12 Si the few times I've used the Range function it NEVER increases from the value displayed when the tank is filled - depending on the prior average mpg it might start at a lower value and hold that number for 50 miles or so before decreasing, or at a high number and decrease by 20 or 30 miles in the next 5 miles, depending on how you drive and traffic condition.

Best not to over-think this and just fill up when you want or when the low-fuel alert comes on.
If you're interested in real mpg numbers, the best way to get them is to consistently fill up at the same pump, using the same procedure each time, and divide miles driven by amount of gas added. (Our real mpg numbers for a full tank of gas vary from 27.4 mpg to 39.9 mpg depending on many variables - from temperature to terrain.)
 

Gruber

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Ideally using the same pump each time at the same time of day in the same weather conditions due to the fact that different pumps have shutoff points and there is some level of density related to temperature. The ideal configuration is actually the way the Mythbusters did their MPG testing, where they weighed the exact amount of fuel they used over a set distance (like they did in the "Golf Ball Dimple Car" Episode).
I've seen that episode and this is really the only way to be accurate to better than +- 1 mpg.
It's not only the repeatability of the pump shut off valve, which is far from perfect even with the same pump, but how do you refill always at the same weather conditions? :hmm:

The shutoff is based on small pressure differences and fluid flow, so it will depend on temperatures of both fuel and air. The shut off mechanism is built to be strong for heavy use. While pumping almost 0.2 gal per second it just can't be so sensitive and quick to be repeatable to a few fl. ounces, as the pump itself should be.

The fuel tank has a vapor space and the tank is filled with air+fuel vapor initially. As you pour colder fuel in a hot tank the air inside cools down and the final vapor space may be smaller or larger at shut-off, depending on the temperature difference between the tank in your car and the tank underground.

My estimate is that even when being very careful, you can't possibly be better than +- 1 mpg when measuring a single tank gas mileage, and double that is quite possible.

Which doesn't mean that car mpg calculations are not set by the manufacturer to be just a bit on the optimistic side.
 

ulieq

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I'm getting somewhere around 36mpg hwh on my 19 civic sport coupe which is as stated. Thats 65-70mph. Of course, if I got 55mph I can get 45mpg, but really who drives that slow?
 

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I've seen that episode and this is really the only way to be accurate to better than +- 1 mpg.
It's not only the repeatability of the pump shut off valve, which is far from perfect even with the same pump, but how do you refill always at the same weather conditions? :hmm:

The shutoff is based on small pressure differences and fluid flow, so it will depend on temperatures of both fuel and air. The shut off mechanism is built to be strong for heavy use. While pumping almost 0.2 gal per second it just can't be so sensitive and quick to be repeatable to a few fl. ounces, as the pump itself should be.

The fuel tank has a vapor space and the tank is filled with air+fuel vapor initially. As you pour colder fuel in a hot tank the air inside cools down and the final vapor space may be smaller or larger at shut-off, depending on the temperature difference between the tank in your car and the tank underground.

My estimate is that even when being very careful, you can't possibly be better than +- 1 mpg when measuring a single tank gas mileage, and double that is quite possible.

Which doesn't mean that car mpg calculations are not set by the manufacturer to be just a bit on the optimistic side.
I drive the same route, fill up after dark Typically around the same time every time after driving for the same amount of time each time and in my Trailblazer I can see down to the same 0.1 MPG tank to tank accuracy (on a vehicle that gets about 14 MPG), the only time I saw a variation in that MPG beyond that number was if I used the pump nozzle on the other side of that unit (pump #1 instead of pump #2). If a gas station was constructed properly the tanks are below the frost line and as such maintain a constant temperature all day around. the weather has much less of an effect on refueling then those internet posts telling you to fill up when it's cold at night making the fuel "denser" would lead you to believe. The Trailblazer sees a 0.5 MPG drop the week they shift to the winter mix then continues at the crappy MPG all winter until they switch back then I get that 0.5 MPG back. My weekly routine is the poster child for doing these tests.

Yes we can't get as accurate as the Myth Busters did but we can get measurably repeatable consistent results if we control everything we can control, i've been using this method for the better part of 2 decades and with the rare special occasion my weekly routine has been the same for the better part of the last 12 years across 4 different cars (not counting the new civic), once I get "calibrated" (ignoring the first refuel average of a new car since the previous fill up wasn't done on my pump of choice) I get repeatable results with multiple different cars so when I say I know this method is more reliable then the onboard computers numbers, i'm not basing this on nothing, i'm basing it on the last like 15-16 years (at least) of driving as I have calculated my MPG for EVERY TANK of fuel I have ever filled up in every car i've owned that had a working odometer. The only exception to these numbers was the time in my 94 Accord where the pump didn't shut off at all and spilled fuel all over the place and the 4 times where the pump was screwed up and kept shutting off way to early (like it wasn't even putting in 2-3 gallons before clicking on a tank I knew needed at least 10 gallons to refuel.
 


Gruber

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I drive the same route, fill up after dark Typically around the same time every time after driving for the same amount of time each time and in my Trailblazer I can see down to the same 0.1 MPG tank to tank accuracy (on a vehicle that gets about 14 MPG), the only time I saw a variation in that MPG beyond that number was if I used the pump nozzle on the other side of that unit (pump #1 instead of pump #2). If a gas station was constructed properly the tanks are below the frost line and as such maintain a constant temperature all day around. the weather has much less of an effect on refueling then those internet posts telling you to fill up when it's cold at night making the fuel "denser" would lead you to believe. The Trailblazer sees a 0.5 MPG drop the week they shift to the winter mix then continues at the crappy MPG all winter until they switch back then I get that 0.5 MPG back. My weekly routine is the poster child for doing these tests.

Yes we can't get as accurate as the Myth Busters did but we can get measurably repeatable consistent results if we control everything we can control, i've been using this method for the better part of 2 decades and with the rare special occasion my weekly routine has been the same for the better part of the last 12 years across 4 different cars (not counting the new civic), once I get "calibrated" (ignoring the first refuel average of a new car since the previous fill up wasn't done on my pump of choice) I get repeatable results with multiple different cars so when I say I know this method is more reliable then the onboard computers numbers, i'm not basing this on nothing, i'm basing it on the last like 15-16 years (at least) of driving as I have calculated my MPG for EVERY TANK of fuel I have ever filled up in every car i've owned that had a working odometer. The only exception to these numbers was the time in my 94 Accord where the pump didn't shut off at all and spilled fuel all over the place and the 4 times where the pump was screwed up and kept shutting off way to early (like it wasn't even putting in 2-3 gallons before clicking on a tank I knew needed at least 10 gallons to refuel.
Your routine is quite amazing, I must admit. :thumbsup: I don't have a routine and my tank to tank readings from same dispenser (when I made them, usually with a new car) varied quite a bit more . Since I don't have a routine, I can't tell whether the differences are due to my driving or any other cause. So my experience is different from yours.

Maybe your truck just uses the same volume of fuel no matter what you do and what fuel you use? You would need to try and get out of your routine to verify this.

I was talking about the difference between gasoline and air temperatures, which is always there and will vary with weather. It may affect the amount of fuel in a full tank much more than just the density of the fuel. But even the temperature of gas itself can't possibly be constant, because the tanks need to be refilled, and quite often. I takes a long time to equilibrate the fresh fuel with the tank temperature. Does your routine involve monitoring the refilling schedule of the gas station? Over two decades even the gasoline composition has been changed by the refineries, so getting exactly the same gas mileage is rather unlikely. Over decades a gas station is also unlikely to be getting its fuel from the same source. Also, the ethanol content (in the same season) is not constant and in fact can vary significantly.
 

fjrman

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The Civic's fuel tank fill hose doesn't connect to the highest elevation on the tank. If you have the car tilted to the right past level the tank will hold more fuel (the air space above the fuel will be smaller). So the side-to-side tilt of the car when filling the tank will affect the max fuel you can transfer.

Maybe on some vehicle tanks the fill hose connects to the top of the tank.

I'd recommend that you check the indicated range just after each fuel fill-up. See if it varies much or is relatively constant.
 

Daniel644

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Your routine is quite amazing, I must admit. :thumbsup: I don't have a routine and my tank to tank readings from same dispenser (when I made them, usually with a new car) varied quite a bit more . Since I don't have a routine, I can't tell whether the differences are due to my driving or any other cause. So my experience is different from yours.

Maybe your truck just uses the same volume of fuel no matter what you do and what fuel you use? You would need to try and get out of your routine to verify this.

I was talking about the difference between gasoline and air temperatures, which is always there and will vary with weather. It may affect the amount of fuel in a full tank much more than just the density of the fuel. But even the temperature of gas itself can't possibly be constant, because the tanks need to be refilled, and quite often. I takes a long time to equilibrate the fresh fuel with the tank temperature. Does your routine involve monitoring the refilling schedule of the gas station? Over two decades even the gasoline composition has been changed by the refineries, so getting exactly the same gas mileage is rather unlikely. Over decades a gas station is also unlikely to be getting its fuel from the same source. Also, the ethanol content (in the same season) is not constant and in fact can vary significantly.
When I do the rare highway trip I do see an increase in mileage on that tank of fuel then it returns to normal and now that my Trailblazer has been reduced to weekend driving duties only I have seen a decline in the MPG on the Trailblazer now that it's trips are shorter and it's more stop and go relative to constantly moving.

also I think we had a little communication breakdown, that wasn't meant to be the same car at the same pump for 20 years, just the same pump with the same car over the 3-7 years I owned said car, like the Trailblazer I got almost 4 years ago now and I've tried my best to always use the same pump but when forced to use the neighboring pump I averaged those 2 tanks once I refilled on my "primary pump", I have changed gas stations over the years but I establish my numbers for the new pump at the new station the one time I switched stations. The important points where the consistency of my daily routine of driving the same routes every day at the same time of day over the course of several years (once adjusted for changing stations or other variables), just like any experiment you have to say the numbers from tanks where you didn't do your routine are invalid data, like if I go out of town and have to fill up at another random station I have HIGHWAY MPG invalidating that tank and the refilling at another station invalidating the following tank, essentially if it's outside of my routine it's invalid numbers for the purposes of comparing week to week MPG averages, I do still see those numbers to average my Highway MPG over the 2 tanks because I KNOW I can based on the ability to see the same MPG's from week to week in my normal driving. The Trailblazer also rarely ever saw the A/C be used since thats another variable (it would maybe only see a few days a year of use at most during summer), I don't have this level of control on the Civic yet as I've changed something with basically every tank, the first 2 tanks I was forced to refill on the other side of the pump (where I know from previous data there is a difference in the shutoff point) and the tank after that I changed the dirty ass Air Filter and this current tank i'm driving the car with the Econ Mode turned on, I've also used the A/C as needed over these last almost 2 months now so thats another variable screwing with my mileage numbers with this car, ultimately I need to get to a point where I don't use the A/C, given I go 2 weeks between fillups it's much more time intensive to get an established baseline for this car to compare tank to tank but given another month or 2 (provided I don't swap tires and have to start over) I will be getting more exact reliable numbers eventually.
 

Daniel644

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The Civic's fuel tank fill hose doesn't connect to the highest elevation on the tank. If you have the car tilted to the right past level the tank will hold more fuel (the air space above the fuel will be smaller). So the side-to-side tilt of the car when filling the tank will affect the max fuel you can transfer.

Maybe on some vehicle tanks the fill hose connects to the top of the tank.

I'd recommend that you check the indicated range just after each fuel fill-up. See if it varies much or is relatively constant.
I saw the estimated range vary by 33 miles from 1 fill up to the next at the same pump.
 


 


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