Dissappointing Fuel Economy

[Tedj101]

I bought my 2010 335d in late November. Since it came with the sports package and we were in Winter, I immediately put a set of Winter Performance tires on.

While my usage was initially mostly commuting, I did go on a couple of trips on the interstate and fuel mileage in all areas was about what I expected and pretty consistent with other users reports here and elsewhere.

In early March I went from my house in Delaware to a friend's house in Northern VA and I averaged 43.7 MPG at the speed limit (60-65) on I-95 using cruise control. Two weeks later, my wife and I drove to Florida in vacation. The only change I made in the car was to change back to the Summer Tires and wheels. From that point on, my fuel mileage has been abysmal.

Initially (with my wife driving but running on cruise control) over the same route I had run 2 weeks earlier, we got 34 MPG. I figured that it would change when I took over the driving. No such luck. For the whole trip to FL running down 95 on cruise control we consistently got 33MPG at 70, 34MPG at 65 and 35MPG at 60. Those readings were so bad that I thought that the computer was off, but hand calculations indicated that the computer was not at fault - the car was using the fuel. Frankly, we would have gotten within a mile per gallon of those figures in her Mazda 6.

I have to attribute the difference to the wider tires, but 8 MPG? One or two I could see, but not a 20% drop! So, what are other people experiencing for mileage with the factory summer tires from the sports package. I see a lot of people getting in the low 40s (as I was) but are they running the sport tire package?

[magbarn]

Assuming, you're running good tire pressures, maybe the rolling resistance on the summer tires is higher? Although I still have less than 8000 miles, my MPG hasn't gone over 32 mpg yet and I have the 18" Sports package setup.

[Tedj101]

Assuming, you're running good tire pressures, maybe the rolling resistance on the summer tires is higher? Although I still have less than 8000 miles, my MPG hasn't gone over 32 mpg yet and I have the 18" Sports package setup.

Tires were set at 35/41 by the book. I agree that there would be a difference in rolling resistance, but should it increase fuel consumption by 20% or more? That sounds way high to me -- which is why I have asked for input from other owners. I appreciate your input. Next time you are on an interstate, would you mind resetting your mileage computer after you are up to speed and report what your mileage was in the 60-70 mph range?

Thanks,
<TED>

[Flyingman]

I bought my 2010 335d in late November. Since it came with the sports package and we were in Winter, I immediately put a set of Winter Performance tires on.

While my usage was initially mostly commuting, I did go on a couple of trips on the interstate and fuel mileage in all areas was about what I expected and pretty consistent with other users reports here and elsewhere.

In early March I went from my house in Delaware to a friend's house in Northern VA and I averaged 43.7 MPG at the speed limit (60-65) on I-95 using cruise control. Two weeks later, my wife and I drove to Florida in vacation. The only change I made in the car was to change back to the Summer Tires and wheels. From that point on, my fuel mileage has been abysmal.

Initially (with my wife driving but running on cruise control) over the same route I had run 2 weeks earlier, we got 34 MPG. I figured that it would change when I took over the driving. No such luck. For the whole trip to FL running down 95 on cruise control we consistently got 33MPG at 70, 34MPG at 65 and 35MPG at 60. Those readings were so bad that I thought that the computer was off, but hand calculations indicated that the computer was not at fault - the car was using the fuel. Frankly, we would have gotten within a mile per gallon of those figures in her Mazda 6.

I have to attribute the difference to the wider tires, but 8 MPG? One or two I could see, but not a 20% drop! So, what are other people experiencing for mileage with the factory summer tires from the sports package. I see a lot of people getting in the low 40s (as I was) but are they running the sport tire package?

Ted, it must be a South Florida thing. I don't get much over 30mpg typically. I have the summer sports tires, but am driving 50/50 cty/hwy. Actually, Florida seems to have too many lights at intersections, and they are timed really long, so you do spend a lot more time at idle, and stopping and going than perhaps some other areas, imo.

Doesn't address your hwy miles though. Were you running A/C?

[Stugots]

Ted, it must be a South Florida thing. I don't get much over 30mpg typically. I have the summer sports tires, but am driving 50/50 cty/hwy. Actually, Florida seems to have too many lights at intersections, and they are timed really long, so you do spend a lot more time at idle, and stopping and going than perhaps some other areas, imo.

Doesn't address your hwy miles though. Were you running A/C?

Mythbusters long ago debunked the myth that A/C affects fuel mileage.

[Penguin]

Mythbusters long ago debunked the myth that A/C affects fuel mileage.

There is no question that A/C impacts fuel mileage. What mythbusters "debunked" was running A/C vs. driving with the windows down instead, increasing drag on the vehicle.

The A/C takes HP, and you simply do not get HP for zero fuel.

[Stugots]

There is no question that A/C impacts fuel mileage. What mythbusters "debunked" was running A/C vs. driving with the windows down instead, increasing drag on the vehicle.

The A/C takes HP, and you simply do not get HP for zero fuel.

Rewatch the show, bud. You're wrong. Last point...saying you lose gas mileage because you have less HP doesn't have make physic(al) sense.

[HIREN]

Did you replace just the tires when switching to the winter set or did you get another set of wheels on winter tires?
The wheel/tire combo weight difference can affect fuel economy and power, but 20% still seems awfully high.
Also your 40+mpg rating, was that indicated or actually measured?

[Flyingman]

Mythbusters long ago debunked the myth that A/C affects fuel mileage.

I'm sorry, I am a mechanical engineer and anyone that says that A/C does not affect gas mileage is smokin somethin!

The A/C compressor is driven off of a fan belt that is in turn driven by the flywheel pulley off the crankshaft, among other items such as the alternator and power steering. It has a magentic clutch that energizes to engage and disengage. When engaged there is an increased mechanical load put on the engine, which is why modern engines have an rpm control that actually boosts rpm when engaged, so engine does not dog down under the additional load.

A/C will absolutely affect the MPG on any vehilce.

Perhaps the story was based on A/C vs having your windows open, which will also increase drag and cause a higher mpg.

C\mon folks, use your brains.

Quote from Edmunds.com
Think Before You Vent(ilate)
Running your air conditioner does cause your vehicle to consume more fuel, but driving with your windows rolled down can be even worse due to the increase of drag on the vehicle. If you are driving slowly, such as around town or in city traffic, then you are better off leaving your windows open, if at all possible. For highway driving, roll up the windows and turn the air conditioning on.

[Stugots]

How about I clarify, for the 'mechanical engineer'. It is not going to affect his gas mileage enough to show the difference between what he got before and what he got after.

Christ, the literalness that people have over here is ridiculously astounding.

The differential between using your AC and not does not create a noticeable difference (opening your windows notwithstanding). An apples to apples, drive the car with A/C and then without, with the windows closed in both instances, will show very similar results.

[Flyingman]

How about I clarify, for the 'mechanical engineer'. It is not going to affect his gas mileage enough to show the difference between what he got before and what he got after.

Christ, the literalness that people have over here is ridiculously astounding.

The differential between using your AC and not does not create a noticeable difference (opening your windows notwithstanding). An apples to apples, drive the car with A/C and then without, with the windows closed in both instances, will show very similar results.

Stugs, Chill man.

A/C use can affect efficiency by 10-20%, excluding running with windows open at speed. If you do a lot of city driving you will see the most effect.

The A/C compressor pulls power from the engine wasting some gas, the effect appears to be minimal in modern cars. The A/C can lower the fuel efficiency from 10 to 20 percent depending on the type of vehicle. Using the air conditioning does require your vehicle to burn more fuel, but it is more efficient than driving with the windows down. Putting the windows down is not a good idea. Putting the windows down tends to increase drag on most cars, canceling out any measurable gain from turning the A/C off. The increased drag of the car means your vehicle will have to work harder, because of the change in the aerodynamics. Therefore, open windows cause your car to burn more fuel.

[Flyingman]

Ambient or outside air temp can also affect performance of a diesel engine, or any engine for that matter. Hotter air is less dense, colder air more dense. Why do you think your car has an intercooler?

Don't mess with the "Mechanical Engineer".;)

[Penguin]

Last point...saying you lose gas mileage because you have less HP doesn't have make physic(al) sense.

It isn't having HP that uses fuel, it's using HP that uses fuel. And A/C compressor uses HP when it is engaged. HP that is provided by the engine, which comes from the heat created by burning fuel.

As a Mechanical Engineer, I can assure you, you are not going to violate the first law of thermodynamics.

Or, to state it as my Thermodynamics professor said many, years ago:

The 1st law says you can't get something for nothing.

The 2nd law says the best you can do is breakeven

The 3rd law says you can't even do that good.

[Penguin]

Christ, the literalness that people have over here is ridiculously astounding.

Hummm. I guess there must be more than one way to read the statement "Mythbusters long ago debunked the myth that A/C affects fuel mileage."

Pardon me for not automatically translating that into "While A/C does affect mileage, it would not account for the large difference you experienced."

[Stugots]

Hummm. I guess there must be more than one way to read the statement "Mythbusters long ago debunked the myth that A/C affects fuel mileage."

Pardon me for not automatically translating that into "While A/C does affect mileage, it would not account for the large difference you experienced."

It's ok...my guess is that you're used to being literal, and that people are just as annoyed by you as I am. :) (seems the ability to multi-quote is a little too difficult for you...let me know if you'd like me to explain that little feature).

There is such a thing as gray areas, and non-absolutes. Outside of the world of mechanical engineering (who know that we have not 1, but 2 of them right here at the 'fest, and they both own d's...what are the odds?), the world does operate outside finite values.

I've said my peace on the subject, and at least Flyingman had some sense of personality (although, I found him initially rude, too...his reply redeemed himself).

I stand by my statement (and I disagree that with our specific cars, as efficient as they are at highway speeds especially, will see a 20% degradation in average consumption). The OP's showed 23.2%, which is beyond comprehension for this vehicle.

[HIREN]

You guys are all retarded! Half this thread has been wasted on pointless AC arguments. Mods should just delete it all.

[Snipe656]

I think we might be more approaching summer blend fuels in all pumps out there. Is the mileage still below from when you first got it?

[Neutrinolad]

Ted, it must be a South Florida thing. I don't get much over 30mpg typically. I have the summer sports tires, but am driving 50/50 cty/hwy. Actually, Florida seems to have too many lights at intersections, and they are timed really long, so you do spend a lot more time at idle, and stopping and going than perhaps some other areas, imo.

Doesn't address your hwy miles though. Were you running A/C?

I get about 30 mpg overall in Florida too, with about 50-50 city-highway driving. This weekend on a trip from Gainesville to Amelia Island and back, however, I got 35.3 mpg, with mainly highway driving.

[Tedj101]

Did you replace just the tires when switching to the winter set or did you get another set of wheels on winter tires?
The wheel/tire combo weight difference can affect fuel economy and power, but 20% still seems awfully high.
Also your 40+mpg rating, was that indicated or actually measured?

I have separate wheels for the Winter tires, but they are also 18". I'm sure the Summer wheel tire combinations are heavier, though.

One quick update, I am now back to my regular driving (primarily commuting to work) and my commuting mileage is significantly poorer than it was when I had the Winter tires on. I am coming to the belief that this situation is normal<G>!

[Snipe656]

Could try switching back and see if things change significantly.

[lalitkanteti]

I too have separate Winter set (tyres-non RFT & rims). After changing to Summer RFT, I have noticed dip in my mileage but its not significant.

[Flyingman]

Not sure what is up this tank but my mileage has dropped from a pretty steady 29-30mpg to about 26mpg. I did have a brutal commute one morning this week due to a car fire that closed an expressway. Major detour and delay.

It's warmed up here in the South so A/C is back on. I'll double check tire pressure.

Road trip coming up soon, so we will finally get some real highway miles.:thumbup:

[Snipe656]

My mileage as dropped a noticeable amount when stuck in bad traffic. I have been running into issues here lately with my mpg changing by 2-3 and think it is fuel quality but that is in my truck.

[sdbrandon]

I bought my 2010 335d in late November. Since it came with the sports package and we were in Winter, I immediately put a set of Winter Performance tires on.

While my usage was initially mostly commuting, I did go on a couple of trips on the interstate and fuel mileage in all areas was about what I expected and pretty consistent with other users reports here and elsewhere.

In early March I went from my house in Delaware to a friend's house in Northern VA and I averaged 43.7 MPG at the speed limit (60-65) on I-95 using cruise control. Two weeks later, my wife and I drove to Florida in vacation. The only change I made in the car was to change back to the Summer Tires and wheels. From that point on, my fuel mileage has been abysmal.

Initially (with my wife driving but running on cruise control) over the same route I had run 2 weeks earlier, we got 34 MPG. I figured that it would change when I took over the driving. No such luck. For the whole trip to FL running down 95 on cruise control we consistently got 33MPG at 70, 34MPG at 65 and 35MPG at 60. Those readings were so bad that I thought that the computer was off, but hand calculations indicated that the computer was not at fault - the car was using the fuel. Frankly, we would have gotten within a mile per gallon of those figures in her Mazda 6.

I have to attribute the difference to the wider tires, but 8 MPG? One or two I could see, but not a 20% drop! So, what are other people experiencing for mileage with the factory summer tires from the sports package. I see a lot of people getting in the low 40s (as I was) but are they running the sport tire package?

My guess is the first reading of 43.7 MPG was inaccurate. Did you measure manually dividing the gas used into the miles driven? Ignore onboard computers as they are rarely accurate.

The car is rated at about 35MPG hwy which is what you are getting so I see no issue. :dunno:

[Snipe656]

I figure out my mpg via my log and compare to the onboard reading with every fillup. This car has been pretty much exactly the same reading as my log, far from the difference he saw.

[Chrisdridley]

When I changed from my Dunlop winter tires back to my Conti tires, I noticed a drop in mpg of about 1.8 - 2.0
I have check the pressures again and they are correct but I am seeing this too......

[Snipe656]

So when you first swapped to winters you saw an increase in mpg?

[Stugots]

Not sure what is up this tank but my mileage has dropped from a pretty steady 29-30mpg to about 26mpg. I did have a brutal commute one morning this week due to a car fire that closed an expressway. Major detour and delay.

It's warmed up here in the South so A/C is back on. I'll double check tire pressure.

Road trip coming up soon, so we will finally get some real highway miles.:thumbup:

Since the car learns driving patterns, adjust shift patterns based on that, and does various other calculations throughout a drive, is it possible that the car gets confused when something that deviates from the norm (such as a 'poor' trip) and as such, that affects future tanks?

I mean...it's one big computer, right?

[Snipe656]

I think it is just because of the constant on/off the accelerator when in really bad traffic and nothing to do with computer confusion. Seems like it is the stop/go stuff that makes the economy on these things do a nose dive.

[Tedj101]

My guess is the first reading of 43.7 MPG was inaccurate. Did you measure manually dividing the gas used into the miles driven? Ignore onboard computers as they are rarely accurate.

The car is rated at about 35MPG hwy which is what you are getting so I see no issue. :dunno:

You have an interesting perspective - my data has to be wrong... I tried to give real figures and conditions to avoid just this sort of response. I thought I indicated that I suspected the computer wasn't working properly but the calculated data corroborated the computer. Oddly enough, I always check what I get with the computer with what I get based on fill ups (which is one of the reasons that I try to avoid using the nozzle adjustment tool) and mine is very very accurate (based on the miles reported by the odometer). Moreover, my Acura, my Dodge RAM and my Honda have computers that are pretty darned close (within a 10th or two) virtually all the time. Apparent inconsistencies from time to time are as likely to be due to imperfect filling procedures as they are to problems with the computer -- in my experience.

As to the 42.7 figure, it checked out at over 42 - after driving around at my friends house and the 125 mile return trip over the same roads. Moreover, it is not an uncommon figure for others on this forum. That is why I originally found it believable and was surprised to see it dissappear under the better conditions that pertain further South on 95.

[Tedj101]

When I changed from my Dunlop winter tires back to my Conti tires, I noticed a drop in mpg of about 1.8 - 2.0
I have check the pressures again and they are correct but I am seeing this too......

Just out of curiosity, do you have the sport package?

[Chrisdridley]

Just out of curiosity, do you have the sport package?

No. I don't have the sport package on either of my 335d's. One thing I did notice is that each winter tire/wheel is 6 pounds lighter than my factory tire/wheel.....would 24 pounds of unsprung weight have this affect???? Some of you engineers chime in on this.