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Old 08-20-2019, 07:16 PM
RPsX5d RPsX5d is offline
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Fuel Mileage - puzzling discrepancy . . . indicated vs. actual/manual

This is more a curiosity question . . .

Back in 2012 (~25,000 miles) when the vehicle was relatively new I compared the indicated mpg on the dash versus the old fashioned method of fill-up to fill-up distance traveled calculations . . . I was very impressed to see the two figures within a tenth of an mpg of each other . . . yes, it was repeatable . . . never saw a difference greater than 0.5 mpg.

The mpg in 2012 was around 23 mpg and it held steady for nearly 100,000 miles.

Then around the summer of 2017 (~110,000 miles), I noticed the indicated mpg had dropped to 19 mpg . . . reset the mpg meter several times and every single time to this day (~151,000 miles) it is pretty much 19 mpg. I can't remember if I did a manual mpg calculation . . .

Now, for a different reason, I started to record the gallons consumed and odometer at fillup . . . a few more keystrokes on the phone and I can get the mpg . . .

Guess what . . . mpg is now back up to ~23 mpg . . . and this has been consistent for the past five or six fill-ups . . .

My guess now is - the actual/real mpg never dropped and it was just the incorrect indicated mpg.

I don't know how the system is measuring the fuel consumed and converting it into mpg . . . there is the mpg "needle" that is very sensitive to how hard you push on the accelerator . . . and then there is the digital display . . . which also is somewhat sensitive . . . you can clearly see it getting updated after a reset . . .

Not sure how the system keeps track of say the fuel consumed for the past 500 miles (approx. matches the manual mpg calculation).

Even less clear what may have changed that causes this longer window mpg error . . . doubt there is a physical problem with one or more sensors as there are zero fault codes of any sort other than the advisory 0452A. Also, the manual mpg calculation is still showing the mpg the car had when it was new . . . so logic says this has to be a computing error . . . not sure how that is possible.

Sure would be nice to know how this discrepancy can be explained . . . anyone?
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Old 08-20-2019, 07:39 PM
Autoputzer Autoputzer is online now
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Driving conditions and behavior can significantly affect fuel economy. Were you buying some kind of bio-diesel fuel when getting low MPG?

The computer controls the pulse duration of each... squirt. It makes an assumption of how much fuel is squirted each time, and assumes that each injector is doing what it was told to do. It counts the squirts and their durations, and estimates the fuel used. It then takes data from the odometer/speedometer to make "since OBC reset" and instantaneous MPG calculations.

If one or more injectors ae squirting more or less fuel than the assumption, that will affect the MPG display. Three of the four of our BMW's have had the displayed MPG steadily increase compared to actual MPG. I suspect the injectors' behavior (fuel per squirt) slightly decreases over time. These changes, if the same across all the injectors, don't affect performance, emissions, or fuel economy because the O2 sensors provide feedback and adjust the fuel mixture to where it's supposed to be.

I never saw a trend with our remaining BMW because it was involved in an unfortunate mishap and I only had it 59 days and 913 miles. I only put gas in it twice.
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Old 08-20-2019, 07:39 PM
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Did your driving habits change? 23 mpg would indicate a lot of highway miles. 19 would have a few more city miles.


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Old 08-20-2019, 09:48 PM
robnitro robnitro is offline
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You need to directly compare, a week of bad traffic etc can change your mpg a lot.

I'm always within 0.5 mpg. Reset trip counter on idrive and I use that to compare at fill up every fill, because a fuel leak or injector issue would skew the calculated mpg so it's a good piece of diagnostic data to watch.
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Old 08-21-2019, 05:47 AM
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The only mileage measure to rely upon is hand calculated, miles driven since last fill-up divided by gallons filled. Carefully recorded with a running analysis of the variation of variations and standard deviation. BMW piezoelectric diesel injection is right at the limits of technology precision.
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Old 08-21-2019, 06:27 AM
icesailor icesailor is offline
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With my 2014 X-1 280 X drive, m MPG goes down as I drive in city traffic, no matter how I drive. I wonder how the drivers who race the Red Light Drag Strip tree. I can beat most any car to the next light. But those spinning Turbo's sure like gas. If you want good consistent gas mileage, drive like your grandfather.

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Old 08-21-2019, 06:56 AM
TroubledGnome TroubledGnome is online now
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Quote:
Originally Posted by Autoputzer View Post
The computer controls the pulse duration of each... squirt. It makes an assumption of how much fuel is squirted each time, and assumes that each injector is doing what it was told to do. It counts the squirts and their durations, and estimates the fuel used. It then takes data from the odometer/speedometer to make "since OBC reset" and instantaneous MPG calculations.
I've heard/read/assumed similar info.

Although my OBC is consistently about 1 mpg lower than my manual calculation.
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Old 08-21-2019, 07:07 AM
icesailor icesailor is offline
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I've always wondered how the onboard computer puts together all of the erroneous information and not fall into Chaos. The only thing I really trust is how many gallons I put in the tank, and what the Odometer says when I re-fill it. Before this latest BMW, I was scrupulous about checking gas mileage. For example, I discovered that you get better overall MPG when you keep the tank full. You have no idea how much fuel vapor is sucked into the engine by the evaporative control system.

Think about it. The less fuel (and more air) inn the tank, the more gas vapors in the tank. The less space for air means less evaporation. Or so my records showed over 75,000+ miles. What was it they said about Computers years ago? GIGO, Garbage In, Garbage Out. Nothing has changed.
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Old 08-21-2019, 07:19 AM
Autoputzer Autoputzer is online now
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I've tracked actual and OBC (on-board computer) MPG's for four cars: three BMW's and a Chevy Cobalt. The correction factor is defined by:

Actual MPG = OBC MPG x (1 + K)

Here are the correction factors since new:

BMW E46 M3: -5.0%
BMW F10 535i: +1.8%
BMW G01 X3 30i: -3.6%
Chevy Cobalt: +0.3%

The K for the M3 was pretty constant. The F10's and the G01's K both drift in the positive direction. The Cobalt's K is drifting in the negative direction, but slowly. It was around +2% when it was new, 123k miles and twelve years ago.

You can't just average the K's for each tank of fuel to get the exact since-new correction factor (Ksn). You have to sum up all the actual fuel used since new, and then calculate the "OBC fuel used" for each tank of fuel (miles / OBC MPG) and sum that up to get "OBC total fuel used." Then, the K since new (Ksn) is:

Ksn = [(OBC total fuel used)/(actual total fuel used)] -1

I'm not sure why you'd need to know the variation of variations, or standard deviation of the K's for each tank of fuel, since the tank K's are weighted differently in compiling the Ksn.

Yes, piezoelectric injectors are extremely accurate. But, an injector is only as accurate as the regulated fuel pressure upstream of the injector. In the case of diesel fuel, the viscosity of the fuel changes more with temperature and that can also affect the flow rates. Injector deposits will change the fuel flow rates, too. Gas pumps are fairly accurate (unless they've been tampered with to cheat you), but there is variation. Also, the gas pump nozzle shut-off point can vary pump-to-pump, and vary with how fast the fuel is being delivered.

With known K's and resetting the OBC MPG and trip odometer at fill-up, I can accurately estimate how much fuel I've burned since the last fill-up. I use this to safely run my tanks to to almost empty without risking running the tank dry. Several times, this has allowed me to get where I'm going on a road trip without having to stop for fuel after dark. This is only a good idea on flat ground, though. We're moving to the mountains eventually, and I'll refill my tanks at probably at ~1/4th of a tank instead of ~1/16th of a tank.

My record mileage for a tank in my 535i was 520 miles, with an actual MPG of 30.2 and an OBC MPG of 29.9. The last 100 miles were through the wilderness, after midnight, and with the outside temperature around +20F... not good conditions for running out of gas. I'd do a fuel burn calculation every time I stopped for food or a piss. The numbers looked good, so I kept on going without getting fuel. I filled up the next morning: 17.2 gallons in a 18.5 gallon tank. My OBC estimated fuel was 17.4 gallons. My K for that tank was +1.14%. My Ksn at the time was +1.17%.

I've suggested to BMW that they put "Fuel Burned Since Reset" as one of the displayed values on the iDrive OBC and Trip Computer screens. They took my (and others') suggestion to replace the bar chart of MPG vs. time with MPG vs. miles.

Last edited by Autoputzer; 08-21-2019 at 01:40 PM.
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Old 08-21-2019, 07:25 AM
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Originally Posted by robnitro View Post
You need to directly compare, a week of bad traffic etc can change your mpg a lot.

I'm always within 0.5 mpg. Reset trip counter on idrive and I use that to compare at fill up every fill, because a fuel leak or injector issue would skew the calculated mpg so it's a good piece of diagnostic data to watch.
Back in the early 1990's, before BMW invented iDrive and even before Microsoft Excel, I caught a problem with a Ford's throttle-body fuel injection, because my MPG dropped about 20%. The cold-start valve, that dumped extra fuel into the intake manifold, was stuck open or partially open.

I had a little black book in the glove box that I'd manually write all the fuel numbers in, along with a cheap pocket calculator. Times were rough back then. You young whippersnappers don't know how easy you have it.

Last edited by Autoputzer; 08-21-2019 at 08:44 AM.
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Old 08-21-2019, 07:32 AM
Autoputzer Autoputzer is online now
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I've always wondered how the onboard computer puts together all of the erroneous information and not fall into Chaos. The only thing I really trust is how many gallons I put in the tank, and what the Odometer says when I re-fill it. Before this latest BMW, I was scrupulous about checking gas mileage. For example, I discovered that you get better overall MPG when you keep the tank full. You have no idea how much fuel vapor is sucked into the engine by the evaporative control system.

Think about it. The less fuel (and more air) inn the tank, the more gas vapors in the tank. The less space for air means less evaporation. Or so my records showed over 75,000+ miles. What was it they said about Computers years ago? GIGO, Garbage In, Garbage Out. Nothing has changed.

The evaporation rate varies with the surface area of the top of the gasoline, not gasoline volume, and that's fairly constant with the fuel level. Temperature and pressure are other factors.

The vapors get burned by the engine. The vapors will richen the fuel mixture. But, that will be adjusted by the O2 sensors. You're also carrying around extra weight, six pounds per gallon of gasoline.

"Garbage In, Garbage Out" was the motto of my high school.
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Old 08-21-2019, 11:16 AM
icesailor icesailor is offline
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Your complicated K-Factors are making my head hurt. Keep it simple but don't be stupid.

In my long years of tracking gas mileage, the only factor I really cared about was what went on the credit card. So you have to measure it over the longest distance you can. I found after a while that I got better gas mileage when I filled the tank at 1/2 full or higher, When I used to run it down to fumes, the MPG dropped noticeably. I had to keep long and careful records though. The only factor that mattered was that there was far less air in the fuel tank. I also noticed that when the tank was empty and maximum air was in the tank, overnight when the air pressure went down overnight and the fuel system had to recharge the tank with more pressure for the evaporative fuel emissions devices, the fuel economy went down. My conclusion was that I wouldn't let the tank get below 1/2. I discovered this over maybe 15 or 20 years with my Ford work vans that I used in my business, BMW emissions systems work the same way. For what it is all worth.

It all has to do with the internal tank pressure. Higher pressures in the tank cause less evaporation of the product. A vacuum will create more evaporation. That's why it is a very bad thing to run a modern car without the pressure cap on the gas tank. Same applies with the cooling system. Its like a steam boiler pulling the condensed water back to the boiler after once being a steam vapor.
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Old 08-21-2019, 12:32 PM
Autoputzer Autoputzer is online now
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Originally Posted by icesailor View Post
Your complicated K-Factors are making my head hurt. Keep it simple but don't be stupid.

In my long years of tracking gas mileage, the only factor I really cared about was what went on the credit card. So you have to measure it over the longest distance you can. I found after a while that I got better gas mileage when I filled the tank at 1/2 full or higher, When I used to run it down to fumes, the MPG dropped noticeably. I had to keep long and careful records though. The only factor that mattered was that there was far less air in the fuel tank. I also noticed that when the tank was empty and maximum air was in the tank, overnight when the air pressure went down overnight and the fuel system had to recharge the tank with more pressure for the evaporative fuel emissions devices, the fuel economy went down. My conclusion was that I wouldn't let the tank get below 1/2. I discovered this over maybe 15 or 20 years with my Ford work vans that I used in my business, BMW emissions systems work the same way. For what it is all worth.

It all has to do with the internal tank pressure. Higher pressures in the tank cause less evaporation of the product. A vacuum will create more evaporation. That's why it is a very bad thing to run a modern car without the pressure cap on the gas tank. Same applies with the cooling system. Its like a steam boiler pulling the condensed water back to the boiler after once being a steam vapor.
So, what's the number? the improvement in fuel economy (%) by filling up at a half-tank instead of at a 1/8th or a 1/16th tank?

Surfing the Interwebs, it looks like gasoline vapor is about four times as dense as air. At STP (standard temperature and pressure) (see level, 15C) the density of air is about 1.225 kg/m3. So, a gallon of gasoline vapor at STP would weigh about 0.04 pounds, where a gallon of liquid gasoline weighs about six pounds. In other words, liquid gasoline is about 150 times as dense as gasoline vapor.

Almost all that gasoline vapor eventually gets burned, burned very efficiently because it's a vapor, and the fuel-to-air ratio of the fuel injection is corrected downward to accommodate the gasoline vapor being burned (by the O2 sensors). So, all the gas you put in your tank gets burned by the engine to make useful power.

If you're filling a 20 gallon tank at half full, your average fuel level is 15 gallons. If you're filling a 20 gallon tank at 1/8th full, your average fuel level is 11.25 gallons. So, if you refill that 20 gallon tank at half full, on average you're carrying around an extra 22.5 pounds of fuel. That will have a small affect on fuel economy, and tire wear, and brake wear...

If you assume fuel use is proportional to the vehicle's weight, lugging that extra 22.5 pounds of gasoline around all the time in your 5000 pound van would reduce fuel economy by about 0.5%.
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Old 08-21-2019, 01:56 PM
robnitro robnitro is offline
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It depends on the vehicle. Some systems aren't so precise with af ratios, so the vapor wouldn't reduce injected fuel.
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Old 08-21-2019, 03:57 PM
Autoputzer Autoputzer is online now
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Originally Posted by robnitro View Post
It depends on the vehicle. Some systems aren't so precise with af ratios, so the vapor wouldn't reduce injected fuel.
O.k., I'll buy that for "some" cars. I bet a BMW's fuel control is precise to a gnat's butt, though.
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Old 08-21-2019, 05:08 PM
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Doug Huffman Doug Huffman is offline
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Fuel economy efficiency is only accomplished with precise control of fuel. Only gassers have to worry about fuel/air ratios.

Diesel piezoelectric injectors make up to seven precise fuel injections per compression stroke.

So, let's see; 1000 RPM is 1 millisecond per revolution. One cylinder makes an exhaust stroke in a millisecond, a power stroke in a millisecond, a compression stroke in a millisecond and an intake stroke in a millisecond. In the millisecond of the compression stroke, at the end of it, are up to seven injections. Divide the stroke in half, into beginning and ending, because I don't know the precise timing of the injections, so seven injections per 500 microseconds. That's about 150 microseconds injection periodicity, or 6.66 KHz PWM at about 200 VAC. I believe that about one thousandth of a liter is injected per stroke, or 7 x 10^-7 liters.

Diesel is 2 C12H26 or 2(144 + 26) = 240 grams per mole - nawp I've had too much wine. A mole is 6.023 x 10^23 molecules here...
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Old 08-21-2019, 06:10 PM
RPsX5d RPsX5d is offline
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Thanks a LOT to everyone for explaining/clarifying many of the questions I had . . . sure appreciate it!

The system, based on the load/demand, etc will pulse diesel in . . . and the system controls the number of pulses, duration of the pulse, rail pressure, etc etc . . . in short, the system knows how much fuel was let in for a certain odometer interval.

Here's where I lose you folks . . .
  • when the car was new, and for the next 100,000 miles or so, the mpg remained at ~23 mpg
  • the mpg continues to remain the same today (~23 mpg) when calculated using the MANUAL method (odometer delta divided by tankful to tankful fuel consumption).
  • To me, the above fact means - nothing has changed physically/mechanically. Any fuel adjustment via the O2 sensor feedback, or any injector leaks, etc should impact BOTH the manual and indicated mpg.
  • Around 110,000 miles, the INDICATED mpg dropped to about 18.5 mpg (later improved to 19.1 mpg) for no apparent reason. To the best I can tell, this happened over a two month period (summer of 2017).
So here's my dilemma . . . reasons like soot buildup around injector nozzle, injectors leaking, etc would/should impact BOTH the manual mpg as well as the indicated mpg - not just the indicated mpg - correct?

Second, unclear to me how the fuel used is the same (based on manual mpg calculation) . . . but the computed mpg changes all of a sudden after nearly seven years and 110,000 miles. i.e. this is basic arithematic . . . feed the same odometer delta and fuel consumed figures, the system should spit out the same indicated mpg - correct?

A few additional clarifications . . .
  • Yes, I should reset the mpg meter each time I fill up, didn't think of doing that . . . started to do it, will report back after two or three fill-ups
  • Never used biofuel on this car . . . and pretty much bought fuel from the same Shell station nearly all (99%) of the time.
  • My driving pattern is very very predictable - typically a 60/40 (city/hwy), pretty much on the same roads, at the same time of the day (run into very little traffic) . . . I do make many trips to the airport and that flips the city/hwy . . . 60 hwy, 40 city, again not much traffic. What I have noticed over the years . . . mpg does not change much, max about 1 mpg.
  • Several folks claim 26+ mpg . . . I have the staggered configuration (Option 214) and the 3rd row . . . the best mpg I ever got was 26+ when driving down I-5, close to Bakersfield (flat), no wind, and setting the cruise at 65 mpg . . .
  • Autoputzer - my "k value" is 0.178, or 17.8% . . . and it has been remarkably stable over the past year or so . . . the worst it ever got was 24.8% . . . a negative "k value" could indicate a leaky injector, etc . . . i.e. fuel is getting lost somewhere.
  • I don't see much mpg difference between summer/winter diesel . . . could be in the Bay Area there isn't much difference.
  • As mentioned previously, I fuel up at the same Shell station and most of the time, at the same pump.
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Old 08-22-2019, 03:40 AM
icesailor icesailor is offline
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I have no great big signatures on my ID. Just my ID. As far as the question I put out,, its just my experience and what I noted over time about the fuel economy in my Ford Econoline E 159 work vans. The only thing that explained the difference was that instead of driving until the fumes were all that was left, I started driving until it was 1/2 full or empty. Liquids do unusual things in pressure or vacuum environments. There must be a reason that if I forget to put the gas cap back on when refueling (I don't forget) all kinds of alarms, bells and whistles go off to remind me to put it back. Like if I forget to close the trunk properly. We're talking over a 10 + year period. If you have an explanation for this, spit it out. All of the vapors go through the engine. The greater the surface area, the greater the evaporation. The tank is either under pressure or a vacuum. I don't know which. Nor do I really care. It is just how the physics of it all work.

In Massachusetts, all gas stations have vapor recovery systems installed at refueling stations. For a reason. In Florida, they don't. For a reason. They are CHEAP and do not give a red donkey's @$$ about pollution.
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Old 08-22-2019, 03:40 AM
icesailor icesailor is offline
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I have no great big signatures on my ID. Just my ID. As far as the question I put out,, its just my experience and what I noted over time about the fuel economy in my Ford Econoline E 159 work vans. The only thing that explained the difference was that instead of driving until the fumes were all that was left, I started driving until it was 1/2 full or empty. Liquids do unusual things in pressure or vacuum environments. There must be a reason that if I forget to put the gas cap back on when refueling (I don't forget) all kinds of alarms, bells and whistles go off to remind me to put it back. Like if I forget to close the trunk properly. We're talking over a 10 + year period. If you have an explanation for this, spit it out. All of the vapors go through the engine. The greater the surface area, the greater the evaporation. The tank is either under pressure or a vacuum. I don't know which. Nor do I really care. It is just how the physics of it all work.

In Massachusetts, all gas stations have vapor recovery systems installed at refueling stations. For a reason. In Florida, they don't. For a reason. They are CHEAP and do not give a red donkey's @$$ about pollution.
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Old 08-22-2019, 07:47 AM
Autoputzer Autoputzer is online now
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Originally Posted by icesailor View Post
I have no great big signatures on my ID. Just my ID. As far as the question I put out,, its just my experience and what I noted over time about the fuel economy in my Ford Econoline E 159 work vans. The only thing that explained the difference was that instead of driving until the fumes were all that was left, I started driving until it was 1/2 full or empty. Liquids do unusual things in pressure or vacuum environments. There must be a reason that if I forget to put the gas cap back on when refueling (I don't forget) all kinds of alarms, bells and whistles go off to remind me to put it back. Like if I forget to close the trunk properly. We're talking over a 10 + year period. If you have an explanation for this, spit it out. All of the vapors go through the engine. The greater the surface area, the greater the evaporation. The tank is either under pressure or a vacuum. I don't know which. Nor do I really care. It is just how the physics of it all work.

In Massachusetts, all gas stations have vapor recovery systems installed at refueling stations. For a reason. In Florida, they don't. For a reason. They are CHEAP and do not give a red donkey's @$$ about pollution.
When you told me to "Keep it simple but don't be stupid," I was pretty sure I wasn't going to get a real answer (a %) when I asked what your fuel economy improvement was by refilling your tank when it was still half full. "K= (A/B) -1" is not overly complicated. There were eight other equations to get to that one.

You don't have any data (i.e. numbers) to back up your assertion, and yet you want everybody on the Interwebs to do what you tell them to do and spend twice as much time hanging around in gas stations... because you said so.

I did a Google search and couldn't find anything credible saying that re-filling a tank when it gets down to half full improves fuel economy. I found a lot websites saying that because of the extra fuel you're carrying around the vehicle's weight goes up, and therefore fuel economy goes down. If you assume a 20 gallon tank, a 5000 pound vehicle weight, and that fuel economy is proportional to vehicle weight (with everything else being the same), then that would work out to a fuel economy reduction of about 0.5%.

I found one link that claimed what you do. But, the author also made the erroneous assumption that the evaporated fuel in the tank escapes into the atmosphere. It doesn't, at lease not on a car made in the last 40 or 50 years.

Last edited by Autoputzer; 08-22-2019 at 07:56 AM.
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  #21  
Old 08-22-2019, 09:11 AM
Autoputzer Autoputzer is online now
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Location: NW Floriduh
 
Join Date: Mar 2014
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Mein Auto: 2014 535i + 2018 X3 30i
O.k., here's something weird.

Post #7 has my since-new OBC MPG errors as percentages. My 535i's actual MPG has been 1.8% better than the OBC says it is. Although, lately it's been on the order of 2.5% better than the OBC says it is. Frau Putzer's X3's MPG is about 3.6% less than the OBC says it is.

The X3 was in for some warranty work, and I asked them to adjust the K factor to 970 from the default of 1000. This should reduce the OBC MPG by 3%. Because of the OBC MPG error is drifting toward 0%, I didn't want to completely correct it by reducing the K factor to 964.

The X3's adjustment was done at 13185 miles, when the tank was about half full. The OBC MPG error at the next fill-up was -1.98%, as I'd expect since the K was only corrected for a half tank of fuel. The next tank of fuel had a correction factor of -0.28%, almost exactly as would be expected. The most recent tank had a correction factor of -1.5%. I'm now tracking the correction factor since 13332 miles, the first fill-up after correcting the K factor, and my OBC MPG error since then is -0.87% (actual MPG 0.87% less than the OBC MPG).

I decided to wrestle with fixing the OBC MPG error on my 2014 535i. Here's a BF thread on how to do it.

https://www.bimmerfest.com/forums/sh...d.php?t=708806

The BF thread has a link to a YouTube video, and the video states that the K factor should be adjusted to:

K = (Actual MPG) / (Displayed MPG) x 1000



My actual MPG has recently been 2.5% higher than my displayed MPG, or my (Actual MPG) / (Displayed MPG) is 1.025. So, I adjusted my K factor from the default 1000 to 1025. I adjusted my K factor at 59314 miles, eight miles after filling the tank.

Here's the weird part. For the two tanks of gas in my 535i since adjusting the K factor, my OBC MPG error has doubled, from around 2.5% to consistent 4.9% to 5.0% (my actual MPG is 4.9% higher than my OBC MPG).

WTF?

The author of Post #14 in BF thread linked above said that his OBC MPG was 6% higher than his actual MPG, and he fixed this by adjusting the K factor from 1000 to 1060. This is exactly the opposite of what the YouTube video said to do. Double WTF? I initially thought the BF-er in Post #14 was wrong. But, it looks like he was right.

It looks like somewhere between building my 2014 535i and building Frau Putzer's 2018 X3 xDrive 30i, BMW's changed the definition of the K factor, to being the reciprocal of what it used to be.

So, I'm gong to change my 2014 535i's K factor again, from 1025 to 975 for the next tank of fuel.

All of the fill-ups since adjusting the K factors on both the X3 and the 535i have been at the same gas pump. So, that's a variability that has been eliminated.

Stay tuned for the results in a couple of weeks. It takes me that long to burn up a tank of gas.
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Last edited by Autoputzer; 08-22-2019 at 01:32 PM.
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  #22  
Old 08-22-2019, 12:40 PM
icesailor icesailor is offline
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Location: Royal Palm Beach, FL
 
Join Date: Jun 2013
Posts: 108
Mein Auto: 2001 325 XI Wagon
You think I care? I've been retired since June of 2013. I did all of this from 1976 to 2000. You see those gasoline tank farms with the tanks full of gasoline product? They all have rubber roofs in them so the gasoline doesn't evaporate from the top. The evaporative control and recovery system puts the tank under a small amount of pressure. You probably consider the cost of gasoline as a necessary evil. Then use the stop lights like a Drag Strip "Tree" Race the other guy to the next red light. I used to live on a place where regular gas was $4.50 gallon and Diesel was well over $5.00 per gallon. Try leaving your B-mmer out in front of the coffee shop running for 10 minutes while you go get a cup of coffee and a muffin. Do that for five days a week. Keep track of your mileage. Then come tell me that you aren't shocked at how much fuel cost you just wasted. That's why Green States like Massachusetts set time limits on leaving your car unattended with the motor running.

I could really care less. It worked for me. I really don't care about you. Because you're smart. And I'm not.
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  #23  
Old 08-22-2019, 01:23 PM
Autoputzer Autoputzer is online now
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Location: NW Floriduh
 
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Posts: 8,828
Mein Auto: 2014 535i + 2018 X3 30i
Actually, using math, the on-board computer, the trip odometer, and a stopwatch, you can precisely determine how much gas your car burns when idling. Guess what, I have a spreadsheet for that too! Somebody on BF asked the question how much gas their BMW burned when idling, and I love a math puzzle.

For the calculation to work, you have to reset the OBC MPG and the trip odometer at the same time. You use the stop watch too measure from the starting OBC MPG decrement (e.g. when the OBC MPG goes from 25.4 to 25.3) and the ending OBC MPG decrement (e.g. when the OBC MPG goes from 24.7 to 24.6).

My 535i uses about 0.4 gallons/hour when idling with the AC on, and about 0.25 gallons/hour with the AC off.

I paid $2.94/gallon for ~91 AKI this morning. So, letting my 535i idle for ten minutes a day, Monday through Friday, with the AC on, would cost me... wait for it...

(50 minutes) x (1 hour/60 minutes) x (0.4 gallons / hour) x ($2.94/gallon)

....... wait for it some more... a whopping $0.98, or one third of a gallon of gasoline per week.

Actually, Frau Putzer goes into Starbucks and gets our stuff, and I wait in my cool and comfy BMW. I'm not a big muffin fan. I really like Starbucks' breakfast sammiches, though. Mmmmm, tasty!

Taxxachusetts also used to have a law that any time the state, a city, county, or town fills a pothole they also have to pay a cop to stand around and watch it being done... and he was usually on overtime.

There's a popular bumper sticker down there: "We don't care how you did it up north."
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Last edited by Autoputzer; 08-22-2019 at 07:09 PM.
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  #24  
Old 08-23-2019, 05:16 AM
icesailor icesailor is offline
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Mein Auto: 2001 325 XI Wagon
That's $50.00 per year. If you saw a $20.00 bill on the sidewalk, would you walk on by or pick it up. When you keep track pf things and not just do it in an arbitrary and capricious manner, you can discover all kinds of interesting things. Like I drove one of my Ford work vans over 100.000 miles. Then I traded it in on another one, That's when I discovered that I had hundreds of pounds of tools in the truck that I might need occasionally that just went on a 100,000 mile ride. Because it was easier to leave them in the truck rather than take them out and put them in the shop. I noticed an immediate improvement in performance. That included gas mileage.

BMW went to RTF's. They are not going back. They like the weight savings. Something that may be hard to figure out with your New Math. I use the old "Retard Math". How many miles did I travel and how many gallons did I use in doing it. I have that Eco-Boost feature. I used it for a while. One time, it said that I went an extra 15 miles because of it. It sure didn't show up in my use/mileage calculations. When I go for a ride, I reset the odometer. Between 70 MPH and under 80 MPH, the trip Odometer says I get over 33 MPG. But the calculations show slightly less. Less if I left the Econo-Boost on. Even less if I drive over 80 MPH,

Back to basics.
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  #25  
Old 08-23-2019, 06:27 AM
Falkon Falkon is offline
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Location: Sugar Land, TX
 
Join Date: Dec 2014
Posts: 250
Mein Auto: 2008 BMW X5 3.0si
I'm curios to know what sort of gas mileages (MPG) people with 2008 3.0si get.

Mine seem to be averaging on the lower tens (11 - 12)MPG City / (14 - 15)MPG Highway
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