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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #1  
Old 05-02-2005, 09:52 PM
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icemanjs4 icemanjs4 is offline
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Gas Mileage experiment

Recently I found myself eyeing the mpg guage a little too often. The results was I found myself driving the BMW like a Camry in order to keep the needle as close to 30 as I could get it. After a week or two I realized I wasn't having as much fun with my car and couldn't figure out why . So finally I decided to perform an experiment with the next two tanks of gas.

The first tank of gas, I always kept the needle close to 30 mpg (within reason). I tried to keep the car in overdrive as much as possible (6 spd manual so I spent a lot of time in 5th and 6th gears). I also used cruise control a lot. It was excruciating!

The 2nd tank of gas I drove without ever looking at the mpg guage. I accelerated hard on the on ramps. I spent more time in 4th on the highway (I even pulled 80 in 3rd a few times - 3rd gear rocks at 5K rpms!). I tried to keep the car within 15 mph of the speed limit, but that was my only sort of restriction.

End result: No difference. I actually got .2 mpg better results on the 2nd tank of gas. The upside is, I had a whole lot more fun in round 2. The bad news is I was getting about 22.2 miles per gallon in a mix of city and highway driving.

Moral of the story? Drive it like you stole it and forget about the gas guage!
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  #2  
Old 05-02-2005, 09:55 PM
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My fuel efficiency in the M3 isn't that much worse than my 325xiT.
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  #3  
Old 05-02-2005, 11:03 PM
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that's interesting. i too sometimes find myself looking at the fun meter way too much and trying to keep it up there. but i never noticed much of a difference either way, i didn't do a formal test like you though, thanks for the info.

i think i'll just tape off the fun meter someday.
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  #4  
Old 05-02-2005, 11:11 PM
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Quote:
Originally Posted by Matthew330Ci
i think i'll just tape off the fun meter someday.
Someone needs to make something that converts it to oil temp.
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  #5  
Old 05-03-2005, 08:39 AM
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Quote:
Originally Posted by icemanjs4
Recently I found myself eyeing the mpg guage a little too often. The results was I found myself driving the BMW like a Camry in order to keep the needle as close to 30 as I could get it. After a week or two I realized I wasn't having as much fun with my car and couldn't figure out why . So finally I decided to perform an experiment with the next two tanks of gas.
I did the same experiment with my car when I first got it. How do you handle 1st gear though? For the first tank did you shift into 2nd easy and at low rpms, and for the second tank did you rev out 1st all the time?
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  #6  
Old 05-03-2005, 08:54 AM
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I have been driving my 02 325Ci for a year now and can't believe how good the gas mileage is. This is the first vehicle that I can drive from Edmonton to Calgary which is about 650 km's (400 miles) on a tank of gas. I usually cruise at 75 mph and notice an extreme difference from my old Acura. It makes having to run premium gasoline a little more tolerable.
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  #7  
Old 05-03-2005, 09:21 AM
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Quote:
Originally Posted by Moderato
I did the same experiment with my car when I first got it. How do you handle 1st gear though? For the first tank did you shift into 2nd easy and at low rpms, and for the second tank did you rev out 1st all the time?
Actually I very rarely ever redline it in first. I just don't feel the power in 1st gear at all. So I'll shift out at about 3-4K into 2nd. From 2nd on is where I changed my driving style. (I wasn't doing 0-60 runs during the experiment, rather checking out differences in daily driving styles).
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  #8  
Old 05-03-2005, 10:27 AM
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Quote:
Originally Posted by icemanjs4
Actually I very rarely ever redline it in first. I just don't feel the power in 1st gear at all. So I'll shift out at about 3-4K into 2nd. From 2nd on is where I changed my driving style. (I wasn't doing 0-60 runs during the experiment, rather checking out differences in daily driving styles).

I've noticed that I can save about 1 - 2 mpg by watching the mpg gauge for a whole tank of gas, but like you said what fun is that? I've found that what really eats into my gas mileage is a lot of trips to 6K rpms , regardless of what gear I'm in. It's so fun to wind out the gears in this car.
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  #9  
Old 05-03-2005, 10:58 AM
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I once drove an 88 honda accord which had a couple rubber engine mounts broken.
The engine would lift itself and try to twist out of position if I accelerated medium hard, so for about a year I drove it with very soft acceleration in 1st and 2nd... - I am talking about feather touch on the gas.
Driving normally I would get about 24 MPG, with the feather touch I was getting about 30 MPG (320miles per tank vs 370 miles per tank)
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  #10  
Old 05-30-2005, 07:21 PM
Adventure Rider Adventure Rider is offline
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I just bought a 325 Ci, and from watching the gas mileage guage, I would guess that it isn't anything fancy, just an intake vacuum guage and therefore loosely related to gas mileage (the more load and more throttle opening you give a car, the lower the vacuum).

Sorry if this has been discussed here before (I am new) or this is obvious, but that is my guess as to that guage.

Again, stating the obvious, but the reason cars get better fuel mileage on the highway is the lack of stop and go traffic - so steady speed and a light foot on the gas pedal is what gets you fuel mileage.

Follow with a good 2 second or more distance and use the throttle to gently modulate your speed instead of following closely and using brakes.

You don't necessarily want to run at the lowest RPMs, but rather at whatever gear and RPM gives you the least throttle while still maintaining the speed you desire. I.E., Lugging it in top gear at 20 MPH is not going to get you good fuel mileage, although coasting down a hill in top gear will.
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  #11  
Old 05-30-2005, 09:33 PM
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Quote:
Originally Posted by Adventure Rider
You don't necessarily want to run at the lowest RPMs, but rather at whatever gear and RPM gives you the least throttle while still maintaining the speed you desire. I.E., Lugging it in top gear at 20 MPH is not going to get you good fuel mileage, although coasting down a hill in top gear will.
Yeah I actually find that its better to keep the car hovering around 3K RPMS. that way if you slow down, you can get back up to speed quickyl with a minum of gas. If your in too high of a gear, you have to burn a lot of fuel for a longer period of time to get back up to speed.

My biggest example is that I have a 2 mile drive every day down a road with a 45 mph speed limit. Naturally I drive at 45 (I'd go faster but I've been bulled over twice for going 50 on this road). Anyway it's often a big tossup as to whether i should stay in 3rd or 4th gear for this cruise. If I use cruise control, 3rd gear is more efficient on this stretch.
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  #12  
Old 05-30-2005, 10:46 PM
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Quote:
Originally Posted by icemanjs4
Actually I very rarely ever redline it in first. I just don't feel the power in 1st gear at all. So I'll shift out at about 3-4K into 2nd. From 2nd on is where I changed my driving style. (I wasn't doing 0-60 runs during the experiment, rather checking out differences in daily driving styles).

Hmm are you sure? I think my zsp really pulls at 5-5.5k in first gear if I floor it. I guess the zhp might be somewhat different on the torque/hp range.
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  #13  
Old 05-31-2005, 02:46 AM
andy_thomas andy_thomas is offline
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Quote:
Originally Posted by Adventure Rider
I just bought a 325 Ci, and from watching the gas mileage guage, I would guess that it isn't anything fancy, just an intake vacuum guage and therefore loosely related to gas mileage (the more load and more throttle opening you give a car, the lower the vacuum).

Sorry if this has been discussed here before (I am new) or this is obvious, but that is my guess as to that guage.
It uses a (buffered) signal from the bit of the DME which opens and closes the fuel injectors. BMW's throttle-less, and therefore vacuum-less, cars (all the Valvetronics and diesels) have exactly the same type of gauge. Mine is pretty accurate, and at over 7 USD a gallon, quite useful.
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  #14  
Old 05-31-2005, 06:12 AM
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Quote:
Originally Posted by startover
Hmm are you sure? I think my zsp really pulls at 5-5.5k in first gear if I floor it. I guess the zhp might be somewhat different on the torque/hp range.
Mine too, the ZSP with the 2.93 rear is gear very tall and if I really want to get going away from traffic I will take 1st up to 6.5K and then shift to second without slipping the clutch, i.e. waiting for the rpms to fall close to 4K before letting the clutch out quickly, but smoothly and that gets me moving away from "normal" cars pretty well without much wear on the driveline.
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  #15  
Old 05-31-2005, 09:15 AM
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My unscientific observations seems to show that its all in your first and second gear starts.

If you get on the gas hard from a stop that seems to have the biggest effect on MPG.

highway roll ons are pretty quickly overcome once you let up on the gas or upshift.
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  #16  
Old 05-31-2005, 03:39 PM
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Quote:
Originally Posted by andy_thomas
It uses a (buffered) signal from the bit of the DME which opens and closes the fuel injectors. BMW's throttle-less, and therefore vacuum-less, cars (all the Valvetronics and diesels) have exactly the same type of gauge. Mine is pretty accurate, and at over 7 USD a gallon, quite useful.
I’ve compared the instantaneous fuel consumption gauge to the OBC over short (1km) runs and there is no difference. They read the same. I’ve checked the actual fuel consumption at fill-up and noticed that the OBC is about 0.5 litres/100km low, about 5% optimistic.

With regard someone else’s comments about fuel consumption and cruise control - In most cases the cruise will give you the best fuel consumption. Note that the cruise control will do what’s necessary to maintain the speed. You can see the increase on an incline. Slowing down a little on the incline would have the best fuel economy.

Fuel consumption gauge - Sometimes I use it. Other times I ignore it. (And have some fun.)

-nv
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  #17  
Old 05-31-2005, 04:12 PM
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I put a tornado in mine and went from 280 miles a tank to 300. Thats considering I drive my car hard most of the time. So I'm pretty sure I can get it to get better mileage if I drive more conservative.
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  #18  
Old 06-01-2005, 08:16 PM
Adventure Rider Adventure Rider is offline
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Quote:
Originally Posted by andy_thomas
It uses a (buffered) signal from the bit of the DME which opens and closes the fuel injectors. BMW's throttle-less, and therefore vacuum-less, cars (all the Valvetronics and diesels) have exactly the same type of gauge. Mine is pretty accurate, and at over 7 USD a gallon, quite useful.
Okay. I noticed that it acted a lot like a vacuum guage, but I was wondering how it worked - I guess I am just used to simpler tech in cars.

Sometimes it blips up (to the right) about halfway when I coast to a stop at a stop light which I assume is some kind of glitch or maybe some logic for the FI to keep the engine from dying after letting off the throttle (I know EFI used to have problems in this area).

Anyway, I don't pay a whole lot of attention to it - the way I normally drive on commutes and in town is fairly efficient anyway from what it says, although I am sure there is no way my car will ever get an actual 12 MPG or worse even though it says it would if I kept driving like that.

I find the engine very smooth at low RPMs and low loads - which lets me creep along in 1st and second in rush hour tie-ups - in first it will pull the car along at idle at a walking pace, where most other cars would buck and stall or at best idle along too fast. Almost as nice as an auto in that regard (and a lot more fun out of traffic).

This is my first tank of gas so I will be interested to see how close the actual fuel mileage is to what the computer thinks I am getting - so far it is 27.5 in mixed driving (25 miles each way to work, about 20 miles of freeway that is often stop and go in the morning and about 5 miles of city driving) and getting better each day I drive it.

I find myself taking my time when driving this car whereas with my old beater Toyota I would rush home - this car is of course a lot more comfortable and enjoyable to spend time in.

I will take on a longer trip in a few weeks when I go out of town for Fathers Day and then see what it does with a lot of highway miles at about 80 MPH. So far I have gotten the impression that at about 65-70 MPH is probably the best for fuel mileage.
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Old 06-01-2005, 09:01 PM
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ACtually I think 80-85 would give better gas mileage - Just a guess tho.
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Old 06-01-2005, 09:16 PM
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Quote:
Originally Posted by bmw330pp
I put a tornado in mine and went from 280 miles a tank to 300. Thats considering I drive my car hard most of the time. So I'm pretty sure I can get it to get better mileage if I drive more conservative.

Read a lot about those. Are they easy to install and what's your experience been so far. They claim HP increase. Is that true
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Old 06-01-2005, 09:23 PM
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Quote:
Originally Posted by icemanjs4
ACtually I think 80-85 would give better gas mileage - Just a guess tho.
Actually, speed quickly kills fuel economy (aero drag per distance increased with square of speed). For example, I did the following experiments on level ground, no wind, over a 50 mile trip segments on same day at roughly the same temp.

Constant 55 mph: 37.5mpg!!! (but painfully slow, but range indicated at 500 miles, with 50 miles already on the tank.)
Constant 65 mph: 34.1 mpg
Constant 75 mph: 28.0 mpg
Constant 132 mph: didn't do long enough for valid reading, but it dropped entire 150 mile trip average almost 2 mpg for a 3 mile foot-to-floor fun.
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Old 06-01-2005, 10:33 PM
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Quote:
Originally Posted by Adventure Rider
Sometimes it blips up (to the right) about halfway when I coast to a stop at a stop light which I assume is some kind of glitch or maybe some logic for the FI to keep the engine from dying after letting off the throttle (I know EFI used to have problems in this area).
When you come to a stop, clutch in, your instantaneous distance traveled decreases but your fuel consumption is constant (at idle), and so the instantaneous fuel economy goes toward 0. When you're actually at 0, the computer stops calculating the instantaneous economy and lets the needle go back to infinity.
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Old 06-01-2005, 10:50 PM
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Quote:
Originally Posted by sunnykk
Read a lot about those. Are they easy to install and what's your experience been so far. They claim HP increase. Is that true
They are very easy to install. You just open up your intake pipe and put it in(Remember to take it off if you go in for service, to avoid any bull$hit if you're still under warranty). I filled up yesterday and got 340 (I usually get 300) on the trip odo from 280 w/o tornado. As for HP, I think you loose it in the low end for some reason, but there is no noticeable gain. I had one on my civic with a CAI and I did notice more pull out of corners. I hope I notice a slight gain when I put a CAI in my 330.
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Old 06-02-2005, 06:33 AM
Adventure Rider Adventure Rider is offline
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Quote:
Originally Posted by FenPhen
When you come to a stop, clutch in, your instantaneous distance traveled decreases but your fuel consumption is constant (at idle), and so the instantaneous fuel economy goes toward 0. When you're actually at 0, the computer stops calculating the instantaneous economy and lets the needle go back to infinity.
Yes - but I meant it that the meter goes to the zero end of the scale (left) and then sometimes it blips up to about 30 MPG for a few seconds before it falls back to zero.
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Old 06-02-2005, 06:48 PM
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Quote:
Originally Posted by Adventure Rider
Yes - but I meant it that the meter goes to the zero end of the scale (left) and then sometimes it blips up to about 30 MPG for a few seconds before it falls back to zero.
The blip is this.

There is a continuous and instantaneous calculation of your gas mileage. At a stop the calculation should produce 0 mpg (far right indication) because that is what you are getting. Just before the stop the needle is in transition to that far right position. BMW choose to display infinite mpg at stop (a far left indication) instead of the true 0 mpg. So as you stop the needle swing to the right (as it should) and then back to the left (by design) when stopped.

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