[Autoputzer]

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/showthread.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

https://www.youtube.com/watch?v=n4e_kaY4E0I&feature=player_embedded

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.

 

[icesailor]

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.

 

[Autoputzer]

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)

***8230;...... 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."

 

[icesailor]

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.

 

[Falkon]

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

 

[Autoputzer]

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.

You're right. What you're describing is what engineers are indoctrinated in, called Lean Six Sigma. "L6S" can be summed up as "large improvements can be gained trough the sum of many small improvements."

American Airlines went on an L6S kick years ago. They saved millions of gallons of jet fuel by not painting most of the outside surfaces of their planes, threw away most of the magazines in the cabin, just carrying enough beverages to get them to the next stop, only carrying enough fuel to get to the next stop with a reasonable margin of safety, etc., etc.

I actually shut the car down and roll the windows down when I'm waiting for Frau Putzer to bring me my hot chocolate and tasty breakfast sammich. Frau Putzer, on the other hand, has no problem sitting in a car with the engine and AC running. I haven't done an idle-fuel-consumption measurement on her X3, but since it's a two-liter (compared to my three-liter), it probably burns about 0.25 gallons/hour with the AC running. We met for lunch Tuesday, and she got there a few minutes before I did. There she was sitting in her car/truck with the motor and AC running.

Our BMW's need 91 AKI gas, but they don't sell it here. So, I make my own by blending 1/3 87 AKI and 2/3's 93 AKI. That saves $3 to $4 per tank, and about $800 over the 100k miles we keep our cars. It takes me an extra minute to do that, but that works out to $120 to $160/hour for my time.

I don't use the recommended tire pressures on the door jamb decals. Instead, I measure the tread depths (each circumferential channel on each tire) when I rotate the tires and adjust the tire pressures for even wear. That almost always means higher pressure than what the decal said. My tires last longer (because they wear evenly), and I get better MPG. I give up some ride quality, though. My top five mileages for a set of tires are: 79k, 74k, 70k, 70k, and 68k miles. The 74k mile tires were on a 1/2 pick-up truck. I'll get ~55k miles out of the OE non-run-flats on Frau Putzer's X3. That means I'll only have to buy one set of tires to get to 100k miles.

If I see a line of cars ahead stopped at a red light, I throw my manual transmissions in neutral and start coasting up to them. Later BMW's (starting in 2014) actually build this logic into EcoPro Mode in cars with automatic transmissions. Planning my stops and using engine braking when possible and necessary, my first BMW still had about 1/3 of the front brake pad material left at 115k miles when I sold it.

Actually, BMW's brought back both spare tires and non-RFT's. You can get a spare tire on every platform BMW makes, except for the F2X 2 Series, F3X 4 Series, and the Z4. The F2X and F3X platforms are old and are nearing the end of their production cycle. Their replacement platforms will likely offer spare tires.

BMW's' spare tire rims are now aluminum to save weight. In addition to improving MPG, they're a lot easier to hump in and out of the trunk, and on and off the car when you have a flat tire. At $150, the optional spare tire is the biggest bargain on a BMW option list. On some models, the spare is free if you spec' the optional non-run-flat tires.

Run-flat tires are about four pounds heavier than a comparable non-run-flat. They also have higher rolling resistance, which reduces MPG by about 1%.

Years ago, I had a rental F-150 with a V8. On a 40 mile road trip I achieved 24 MPG. But, on the same road trip in Frau Putzer's 2018 X3 in EcoPro, I can hit 38 MPG if the traffic lights and wind are in my favor.

One thing that really cuts into MPG is sitting at stoplights with the engine running. But, I always disable the Auto Start/Stop (ASS). Yeah, ASS saves gas. But it also puts extra wear on the engine, starter, and turbocharger. Since we keep our cars 100k miles, I don't want to risk having to replace those components.

Frau Putzer once found a $100 bill on the ground. She damn well sure did pick it up. But, then she said "Look ever' body, I found $100!" I told her to STFU, in case the person who lost it was still around.

A friend if mine found a bail of marijuana floating in the water when he was surfing. He lugged it back to the frat' house and dried it out. Him and his frat' buddies smoked half of it and sold the other half.

 

[RPsX5d]

. . . 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 . . .

Thanks a lot for bringing this up, I had totally forgotten about this one . . . initially (2012-ish), when I did the pump mpg (calculated) vs OBD mpg (indicated), I remember reading about this correction factor . . . when the discrepancy appeared in 2017 I had completely forgotten about the k-factor . . . and not sure why I didn't do the obvious - recheck the pump mpg vs. OBD mpg readings . . . instead, I assumed something had fundamentally changed in the system, most likely a sensor was feeding the system incorrect information . . . and tried to reason out logically what may have happened . . . back then and as it is now, there were no fault codes . . . so after a while, I simply gave up and decided to wait for a fault code to show up, none so far.

That's the best part of this forum . . . post an issue, initial post may not be perfect, but once the more experienced folks start to chime in, more often than not, it gets you an answer or at least point you in the right direction . . . I have been on this forum since 2010, and that has been my experience most of the time.

THANKS to everyone who contributed in a productive manner . . . for now, I will check pump vs OBD mpg for a few more fill-ups . . . I always saw a significant drop in mpg as a sign of something is giving out . . . and if pump mpg is about the same as it was when the vehicle was new, I will call it a day . . . may mess with the K-factor for the fun of it . . .

PS: I found BF a few months after I bought this X5 . . . if I had known about this before my purchase, I would have definitely asked about the adaptive drive, and most likely would have got it . . . was fed some REALLY bad info by three separate sales guys, made me wonder . . . and finally did not get it . . . SORELY regret it!

 

[Autoputzer]

The new definition of K used on Frau Putzer's 2018 X3 makes more sense: Lower the K to lower the displayed MPG, increase the K to increase the displayed MPG.

But, most of the world doesn't think about fuel economy (i.e. distance/volume of fuel, e.g. MPG). The rest of the world thinks about fuel consumption ( i. e. volume of fuel/distance traveled, e.g. liters/100km), and that's what's displayed on the OBC and Trip Computer. For cars that display fuel consumption, the old definition of K used on my 2014 535i makes more sense.

This whole fuel economy vs. fuel consumption is why our analog MPG displays go to infinity when we come to a stop, even though MPG when stopped is zero. The internal logic of the computer is really computing fuel consumption, and then takes the reciprocal of that value to display as fuel economy. At idle, fuel consumption (fuel volume/distance) is infinity, where fuel economy (distance/fuel economy) is zero. But, computers don't like it when you divide any number by zero. So, the needle or analog display of MPG sort of "runs home to Mama" as ST2 Jones said on the USS DALLAS in "The Hunt For Red October."

 

[icesailor]

In MY experience, that "City Mileage" and "Highway Mileage" is a different animal. Regardless of what the phake ad says on the window at the dealer's lot, my experience with my 2001 325XI wagon throughout its life time was that it got as low as 16 MGH (or lower in city stop ang go traffic, and 28 MPG on an Interstate as long as I kept the speed around 75 MPG. If you want to get worse gas mileage, drive faster. Maybe yo can afford to piss your money away for the Oil Baron Crime Syndicates.

My 2014 X-1 280 X Drive gets 18.0 in the same city stop and go driving but gets 32+ MPG when driving on limited access Interstates when I keep it between 74 MPH and 78 MPG. When you pot your big hoof into that thing on the floor to the right, and those twin turbo's start spooling up and the BOOST goes up, you can almost watch the Computer drop the MPG's. Cruise Control can help. But you still need to give it a little speed when you come to a hill. Like towing heavy horse trailers with almost well enough horse trailers.

 

[Autoputzer]

Here are my results of adjusting the OBC MPG.

I had the dealer do our 2018 (G01) X3, since it's under warranty. Before adjustment, the error was -3.6% (actual MPG was 3.6% less than the OBC MPG). I had the dealer adjust the K Factor from 1000 to 970. After adjustment and three tanks of gas at the same pump, the error now is -0.2%.

My 2014 (F10) 535i took two tries. I found out that the definition of the "K Factor" is the reciprocal of what it is for the 2018 (G01) X3. Before my first adjustment, the recent error was about +2.5% (actual MPG was ~2.5% more than the OBC MPG). I adjusted the K Factor from 1000 to 1025. But, that caused the error to increase (actual MPG being ~5% more than the OBC MPG). So, for the third tank of fuel, I adjusted the K Factor from 1025 to 975. I filled up the car this morning, and the MPG error was -0.23%. Actually, part of that error was round-off of the odometer mileage. The actual trip odometer mileage was 432.6 miles, but 432 is used by the spreadsheet to calculate MPG. Using 432.6 miles, the OBC MPG error would only be -0.1%. Also, my favorite pump was shut down and I had to use another one.

The gas station I use is about six miles from my house, near Hardee's. Gas there is about $0.15/gallon cheaper than near my house. I combine a Top Tier Gas run with a top tier biscuit run to the nearby Hardee's. I leave the house about 6 a.m., so there's no traffic. I take the coastal road which has fewer traffic lights and a 35 MPH speed limit. On the X3, from the house to the gas station, I get about 36 MPG with the AC on. Today, in the 535i, the house to gas station run got me 30.4 MPG.

I blend my gas to get 91 AKI. This morning my actual fuel purchased was only 0.02 gallons off of my prediction (from the OBC MPG and the trip odometer).

 

[RPsX5d]

I wonder what (if anything) would cause the K-factor effect to change? i.e. once set to match manual calculation, why would the two readings drift apart?

For several years, my indicated reading and manually calculated values pretty much matched . . . about 22.5 mpg. This value held for a very long time (several years). Then suddenly the indicated dropped to about 18 mpg, and as I indicated above I didn't repeat the manual calculation . . . I assumed something was going wrong, however, no fault codes.

I am now rechecking indicated vs. manual . . . two tanks done . . . both showing the indicated around 18 mpg . . . manual about 22.5 mpg, same as what it has been for a very long time.

One possibility is after resetting the K-factor your drive profile has changed substantially, re-adjust the K-factor to match the new drive profile. In my case, the drive profile did not change, same fuel station, etc . . .

 

[icesailor]

I have always used the "Retard" or Short Bus Calculations method. If I drive 10 miles and use 1 gallon of gas, I am getting ten miles per gallon. If I go to a gas station and fill the tank to the very tippy-top (so no more will go in) and drive 10 miles to the next gas station and refill the tank to the very tippy-top and it takes 0ne gallon to fill it. I got 10 MPG. Or so we riders of the short bus might calculate. Fill the tank to the very top and let it sit over night. Gas up. Whatever you have to add is evaporation plus what you consumed getting to the gas station. On multiple attempts. Same as with fuel consumption when idling. Fill up your tank and go directly to the coffee shop. Leave the engine running for as long as possible to keep the car hot or cold. Then go top it off. You might be surprised at how much fuel is consumed. Some of that is consumed by the evaporative fuel recovery systems. Like in the States that made the vas stations install vapor recovery systems on the fuel hoses. They didn't do it to make the dealers spend money. In spite of what the opposition tells you.

Keep it simple,, but don't be stupid. All of those "K" Factors can give you a headache. And the poor technician that doesn't have the time to tweak things like you want them to.

 

[Gary214]

You're right. What you're describing is what engineers are indoctrinated in, called Lean Six Sigma. "L6S" can be summed up as "large improvements can be gained trough the sum of many small improvements."

American Airlines went on an L6S kick years ago. They saved millions of gallons of jet fuel by not painting most of the outside surfaces of their planes, threw away most of the magazines in the cabin, just carrying enough beverages to get them to the next stop, only carrying enough fuel to get to the next stop with a reasonable margin of safety, etc., etc.

I actually shut the car down and roll the windows down when I'm waiting for Frau Putzer to bring me my hot chocolate and tasty breakfast sammich. Frau Putzer, on the other hand, has no problem sitting in a car with the engine and AC running. I haven't done an idle-fuel-consumption measurement on her X3, but since it's a two-liter (compared to my three-liter), it probably burns about 0.25 gallons/hour with the AC running. We met for lunch Tuesday, and she got there a few minutes before I did. There she was sitting in her car/truck with the motor and AC running.

Our BMW's need 91 AKI gas, but they don't sell it here. So, I make my own by blending 1/3 87 AKI and 2/3's 93 AKI. That saves $3 to $4 per tank, and about $800 over the 100k miles we keep our cars. It takes me an extra minute to do that, but that works out to $120 to $160/hour for my time.

I don't use the recommended tire pressures on the door jamb decals. Instead, I measure the tread depths (each circumferential channel on each tire) when I rotate the tires and adjust the tire pressures for even wear. That almost always means higher pressure than what the decal said. My tires last longer (because they wear evenly), and I get better MPG. I give up some ride quality, though. My top five mileages for a set of tires are: 79k, 74k, 70k, 70k, and 68k miles. The 74k mile tires were on a 1/2 pick-up truck. I'll get ~55k miles out of the OE non-run-flats on Frau Putzer's X3. That means I'll only have to buy one set of tires to get to 100k miles.

If I see a line of cars ahead stopped at a red light, I throw my manual transmissions in neutral and start coasting up to them. Later BMW's (starting in 2014) actually build this logic into EcoPro Mode in cars with automatic transmissions. Planning my stops and using engine braking when possible and necessary, my first BMW still had about 1/3 of the front brake pad material left at 115k miles when I sold it.

Actually, BMW's brought back both spare tires and non-RFT's. You can get a spare tire on every platform BMW makes, except for the F2X 2 Series, F3X 4 Series, and the Z4. The F2X and F3X platforms are old and are nearing the end of their production cycle. Their replacement platforms will likely offer spare tires.

BMW's' spare tire rims are now aluminum to save weight. In addition to improving MPG, they're a lot easier to hump in and out of the trunk, and on and off the car when you have a flat tire. At $150, the optional spare tire is the biggest bargain on a BMW option list. On some models, the spare is free if you spec' the optional non-run-flat tires.

Run-flat tires are about four pounds heavier than a comparable non-run-flat. They also have higher rolling resistance, which reduces MPG by about 1%.

Years ago, I had a rental F-150 with a V8. On a 40 mile road trip I achieved 24 MPG. But, on the same road trip in Frau Putzer's 2018 X3 in EcoPro, I can hit 38 MPG if the traffic lights and wind are in my favor.

One thing that really cuts into MPG is sitting at stoplights with the engine running. But, I always disable the Auto Start/Stop (ASS). Yeah, ASS saves gas. But it also puts extra wear on the engine, starter, and turbocharger. Since we keep our cars 100k miles, I don't want to risk having to replace those components.

Frau Putzer once found a $100 bill on the ground. She damn well sure did pick it up. But, then she said "Look ever' body, I found $100!" I told her to STFU, in case the person who lost it was still around.

A friend if mine found a bail of marijuana floating in the water when he was surfing. He lugged it back to the frat' house and dried it out. Him and his frat' buddies smoked half of it and sold the other half.

:rofl::rofl::rofl:



I really enjoyed your post.

Frau Putzer must be one cool lady

Why blend 1/3 and 2/3 ??

I would assume that 50- 50 of 87 and 93 gas would make it 91 gas :dunno:

 

[Doug Huffman]

LOL

https://en.wikipedia.org/wiki/Lean_Six_Sigma

 

[Autoputzer]

I wonder what (if anything) would cause the K-factor effect to change? i.e. once set to match manual calculation, why would the two readings drift apart?

For several years, my indicated reading and manually calculated values pretty much matched . . . about 22.5 mpg. This value held for a very long time (several years). Then suddenly the indicated dropped to about 18 mpg, and as I indicated above I didn't repeat the manual calculation . . . I assumed something was going wrong, however, no fault codes.

I am now rechecking indicated vs. manual . . . two tanks done . . . both showing the indicated around 18 mpg . . . manual about 22.5 mpg, same as what it has been for a very long time.

One possibility is after resetting the K-factor your drive profile has changed substantially, re-adjust the K-factor to match the new drive profile. In my case, the drive profile did not change, same fuel station, etc . . .

My guess is that variations in fuel pressure is the biggest factor, followed variations in the injectors and deposits building up in the injectors restricting flow. Our current two BMW's OBC MPG/actual MPG is slowly drifting up, suggesting that fuel flow (and maybe fuel pressure) is going down slightly with time. For diesels, fuel viscosity changes with temperature could be significant.

 

[Autoputzer]

LOL

https://en.wikipedia.org/wiki/Lean_Six_Sigma

When I was L6S indoctrinated, the boogiemen were: transportation, retooling, inventory, rework, and inspection. The thing is that each one of the boogiemen is a cure for at least one of the other boogiemen. The problem is that L6S-ers get fixated on eliminating just one of the boogiemen, and accidently let the other ones grow into monsters.

I managed SONAR system that had portable test sets about the size of a large ice chest. They made enough of them during initial production to last 25 years. Each of the 21 ships with that SONAR got one, and the rest, maybe ten, were stacked in a warehouse in Pennsylvania. The spare parts guy called me up one day, saying that their warehouse management algorithm told him to throw all of them away. He figured he'd better call me first, though. To replace those ten test sets would cost maybe $1M, considering all the necessary design refresh and re-tooling costs. So, the algorithm was going to throw away $1M of stuff to free up literally about 15 square feet of floor space.

 

[Autoputzer]

:rofl::rofl::rofl:



I really enjoyed your post.

Frau Putzer must be one cool lady

Why blend 1/3 and 2/3 ??

I would assume that 50- 50 of 87 and 93 gas would make it 91 gas :dunno:

1. Thanks.

2. She has her moments.

3. Octane is roughly a weighted average:

https://www.sunocoracefuels.com/tech-article/mixing-fuels-calculating-octane

A 50%/50% blend of 87 AKI and 93 AKI would get you 90 AKI.

A 50%/50% blend of 89 AKI and 93 AKI would get you 91 AKI.

A 33%/67% blend of 87 AKI and 93 AKI would get you 91 AKI, and generally be a little cheaper than the 50%/50% blend of 89 AKI and 93 AKI.

Gas pumps make 89 AKI from a 67%/33% blend of 87 AKI and 93 AKI, or a 50%/50% blend of 87 AKI and 91 AKI. But, they generally charge disproportionally more for 89 AKI.

 

[Gary214]

1. Thanks.

2. She has her moments.

3. Octane is roughly a weighted average:

https://www.sunocoracefuels.com/tech-article/mixing-fuels-calculating-octane

A 50%/50% blend of 87 AKI and 93 AKI would get you 90 AKI.

A 50%/50% blend of 89 AKI and 93 AKI would get you 91 AKI.

A 33%/67% blend of 87 AKI and 93 AKI would get you 91 AKI, and generally be a little cheaper than the 50%/50% blend of 89 AKI and 93 AKI.

Gas pumps make 89 AKI from a 67%/33% blend of 87 AKI and 93 AKI, or a 50%/50% blend of 87 AKI and 91 AKI. But, they generally charge disproportionally more for 89 AKI.

:thumbup::thumbup::thumbup:

Very good info. I am going to use this to fill my x5 :angel:

 

[RPsX5d]

My guess is that variations in fuel pressure is the biggest factor, followed variations in the injectors and deposits building up in the injectors restricting flow. Our current two BMW's OBC MPG/actual MPG is slowly drifting up, suggesting that fuel flow (and maybe fuel pressure) is going down slightly with time. For diesels, fuel viscosity changes with temperature could be significant.

Not disagreeing with you . . . only trying to understand what is happening in my case . . .

In my case, initially and for several years (up to about 110,000 miles) both indicated and manual mpg tracked pretty well . . . within a tenth of an mpg.

If, as you suggest, deposits, injector, etc is causing an issue - i.e. what the computer commanded does not match the fuel delivered, then yes, I agree the indicated mpg would be off.

But in my case, the manual mpg continues to remain the same as before . . . indicating no serious deposit buildup or injector issues - i.e. everything is running as before, only indicated mpg changed.

If there were some real issues like deposits and/or injector issues . . . I would have expected the manual mpg to also change as the actual fuel delivered is different. i.e. how can the deposits only impact the indicated mpg and not the manual mpg?

 

[Autoputzer]

Not disagreeing with you . . . only trying to understand what is happening in my case . . .

In my case, initially and for several years (up to about 110,000 miles) both indicated and manual mpg tracked pretty well . . . within a tenth of an mpg.

If, as you suggest, deposits, injector, etc is causing an issue - i.e. what the computer commanded does not match the fuel delivered, then yes, I agree the indicated mpg would be off.

But in my case, the manual mpg continues to remain the same as before . . . indicating no serious deposit buildup or injector issues - i.e. everything is running as before, only indicated mpg changed.

If there were some real issues like deposits and/or injector issues . . . I would have expected the manual mpg to also change as the actual fuel delivered is different. i.e. how can the deposits only impact the indicated mpg and not the manual mpg?

The performance of sensors and electronics "drift" over time. Precision electronic instruments typically have to be periodically calibrated to function properly. I worked on automated test equipment that needed to be calibrated about every six months. We'd spend a day getting everything dialed in perfect and working great. In a few months, the equipment would start acting up again and need calibration again. We'd schedule re-calibration for every six months. But, with heavy use the equipment needed more frequent calibration.

Both of my direct-injected BMW's have had the actual MPG steadily increase when compared to the indicated MPG. My 535i started out just about perfectly accurate. After 60k miles, the actual MPG was about 2.5% higher than the indicated MPG. The X3 started out with the actual MPG being about 5% less than the indicated MPG. But, it steadily became more accurate. After about 13k miles, the actual MPG was only about 3.5% less than the indicated MPG. In both cars, the trend was that the fuel injection was delivering less and less fuel (better actual MPG) over time than the computer "thought" it was delivering.

I started tracking OBC MPG error in my old port-injected BMW from about 40k miles, and up to 115k miles when I sold the car. The error was more consistent than with my two direct-injected BMW's, with actual MPG being about 5% less than the indicated MPG.

The performance of mechanical systems also change over time. Back in the bad old days of carburetors, mechanical distributors, and ignition "points," cars needed tune-ups to stay running something close to right. A big breakthrough was the invention of the O2 sensor. That "feedback" allows electronic fuel injection systems to sort of continually tune themselves, and correct for the measurement errors and performance variations in the systems.