Fuel mileage

[bmw327]

Hi Folks -

Just wanted to relay some fuel mileage data...

I've been driving my car as a daily commuter (mixed hwy / city) since the beginning of April and have been keeping records of fuel consumption since purchase.  I've filled the car 11 times since purchase and for the last tank (#10), I changed a few things to see  how they collectively might affect fuel mileage.

For all but the last tank of fuel, I drove as normal and I had an average fuel mileage of 25.3 with a standard deviation of 0.86 mpg (%RSD of 3.42%).  Total miles = 2601

For the last tank I've made the following changes and for the most part have maintained discipline:

1.  Raise tire pressures 4 psi all around to 36 psi.

2.  Use the AC only when absolutely necessary and turning the AC off when accelerating from a stop.

3.  Reducing hwy cruising speeds from 75-78 mph to 70-72 mph (indicated).

4.  Accelerating at wide open throttle as much as possible (except in first) but short shifting; max rpm ~4200. Apparently this is a pretty efficient way to do it from a few articles I've read.

5.  Raising cornering speeds when safe to do so - less braking going and faster cornering means less acceleration required on the way out.  I've gotten a few cloverleafs down to zero braking / zero shifting when traffic permits.

6. Drive one gear higher than I ordinarily would.

This has yielded 27.2 mpg, which is a 7.5% improvement over my average, better than 2 std deviations above the mean of the first 9 tanks, and 3.8% better than my previous best of 26.2 mpg.

Ok, I'm a geek.  I admit it.  Still, I thought you might be interested...

[vonkamp]

Good data. I think your highway driving must be knocking down your mileage a bit. Most of my daily driving is @ 45 to 55mph and I am getting 30 + mpg even with my ac on in this Florida heat. I also fixed all my vacuum leaks and that seemed to help as well...
Next up is tjts1 cold air intake conv., COP's, and Magnaflow muffler.

[bmwman91]

Slowing down 5mph on the highway makes a hell of a difference!  I try to keep it between 65 and 70mph, although sometimes I just go 80-85mph when driving longer distances on weekends lol.  Commuting generally gets me better mileage since I am moving slower.

On surface streets, strategize a little.  I coast a LOT between stop signs and lights.  Usually, I accelerate to 5 or 10 above the limit and coast to the nest stop.  Engine braking saves a little fuel as well.  At some of the longer lights in town, or ones where where is a long line of cars, I turn the motor off lol.  I always feel like a goober, but who gives a damn, really.

I get between 28 and 31mpg consistently.  I am excited about the next tank though.  I am hoping to beat 31mpg!

[Alexx]

My 1991 BMW 318is takes less than 10 liters to do 100 kilometers.

[batsbats]

I used to WOT and short shift on my prelude.  I read it in C&D a long time ago.

I'm consistently getting 26-27mpg with 60hi/40city on my 318is

[bmw327]

The car is in good tune with no vacuum leaks whatsoever. The mess under the intake was checked recently, two hoses were replaced, and it's dead smooth, though there are a few things potentially working against it.  

First, 10 miles of my 32 (one way) commute are on a 55 mph road with quite a few lights (12, I think) and a fair amount of traffic, meaning there is quite a bit of acceleration to ~60mph, sometimes more, then deceleration. Maintaining anything like a constant speed on that road is impossible and that will eat fuel.

Second, the car is wearing relatively wide tires for its size (205-55-15) possibly giving slightly greater rolling resistance and poorer aerodynamics.

Third, the car has a 93 octane chip which definitely produces more power than the stock unit.  I don't know if this has had any effect on fuel consumption but because it does change ignition and fuel mapping, I'd assume the potential is there.  Any data from Mark D on this?  

Old EPA ratings for the car were 19 / 25 mpg city / hwy, so I think ~27 mpg in mixed driving is pretty good.  

It beats the 19-20 mpg that my 535i was getting...but I miss the torque sometimes!

[Alexx]

Petrol crisis.

[tjts1]

Excellent data. Thanks for sharing it.
I think the EPA numbers are really unreliable for this car. My all time worst tank was 26mpg and I was flogging the car down highway 1 along the northern coast of California. Most tanks fall in between 29-31mpg. 90% of my driving is short city and highway trips of no more than 5-10 miles at a time. I tend to avoid rush hour and it usually takes me about 2-3 weeks to cover the 340-360 miles when my low fuel light comes on. My all time best was 35mpg on a highway only tank. I only buy 87 octane.

[bmwman91]

I just drove the 60 miles to my GF's place last night.  The mileage needle our cars have is the greatest thing ever lol.  During the drive, I kept it pegged at ~35mpg the entire time, save a couple surface streets and idiots on the highway merging at 40mph.  My speed was kept between 65 and 75mph.  For now, maximizing economy feels more like a game than anything...it actually kills time quite well to challenge myself to get the best mileage possible!

[Sam Cogley]

Excellent data. Thanks for sharing it.
I think the EPA numbers are really unreliable for this car. My all time worst tank was 26mpg and I was flogging the car down highway 1 along the northern coast of California. Most tanks fall in between 29-31mpg. 90% of my driving is short city and highway trips of no more than 5-10 miles at a time. I tend to avoid rush hour and it usually takes me about 2-3 weeks to cover the 340-360 miles when my low fuel light comes on. My all time best was 35mpg on a highway only tank. I only buy 87 octane.

The EPA numbers are horribly unreliable for any manual transmission vehicle.  Either whoever is doing the testing has NO idea how to drive a stick, or someone there is being paid off by the automatic transmission manufacturers.

[gearheadE30]

Lol, it is kinda fun on the highway. I have found that toyota landcruisers offer the longest drafting range behind the vehicle out of all mass-produced SUV's, but it is more efficient to drive behind a new tahoe or suburban, because they have a smoother draft . ~30 ft behind a semi yeilds the same gains as ~15 ft behind a landcruiser. With drafting, I can average 45 mpg on the highway, and that is at reletively safe distances with no cruise, 93 octane chip, and a 4.10 diff.

City, I get consistently 26 mpg. Round trip from Fishers to Terre Haute (about 4 hours) got me an average of 40.13 mpg. I need to get a life

[tjts1]

You must have nerves of steel. I tried drafting behind a semi once in our volvo wagon. It was amusing seeing the instant MPG display show mid to high 40s but my god i was bored. I had to cruise at 120mph for the next 15 minutes just to clear my head of the mind numbing experience.

[AcSchnitzer318is]

City... between 24-27mpg.  Highway 28-33mpg.  I just recently changed to the 19# mustang injectors so we'll see if that netted or cost me any mileage.  Oh running 93 octane chip and delta regrind cams.

[EN318isPDX]

I get 31mpg consistently since i replaced my fuel injectors, fuel pump and fuel filter. Before that i was lucky to get around 15-25 mpg with all the vacuum leaks and lack of correct fuel pressure. Also consider what type of fuel you run. I know in my 1977 280z if i run regular i get about 4 less MPG than if i 92 octane.

[Bunta]

Ive been getting 27mpg lately.  Thats mostly back roads and a bit of highway driving. Not getting on it too much.  
Its fun trying to get the best mileage possible.  Ive managed 34mpg before, lots of coasting an 2k rpm shifts.  





Hunter