Should the EPA Have Changed the BMW 328's Mileage?

Bmw3seriesmileage

When the EPA downgraded the highway mileage estimate for the new BMW 328 to 33 mpg from 36 mpg, it was a big deal. Automakers don't routinely see that kind of change from the agency when releasing a new model. The turbocharged four-cylinder engine — teamed to an eight-speed automatic transmission — is vitally important to the automaker, as it is now the base engine for the company's most popular car.

When a new 2012 328i arrived at Cars.com HQ for testing, I took it home, loaded my kids in their child-safety seats and headed off for the highway for a bit of an unscientific real-world test. I don't think the EPA got it entirely right this time out.

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The destination was an indoor play place that allows two young children a safe haven to exhaust their nearly endless energy. This one is far from our house, 23 miles, but it's a favorite destination, so the ride for the kids — passing the airport and two train yards — wasn't a hardship.

Along with their car seats, I'd estimate that they accounted for an extra 100 pounds or so of weight. The weather was cool but sunny, so I had the air conditioning on at a medium level. Winds were strong, though. Heading north and later south, there were crosswinds and the buffeting was easily felt.

On the trip down and back I maintained a steady clip of around 65 to 70 mph, rarely breaking 70 mph. I did not have the optional Eco mode on, which regulates the HVAC system.

Leaving the highway after 20 miles, the trip computer registered 34 mpg and settled at 34.2 by the time we reached the destination three miles later, driving at a moderate speed with few stops.

On the trip home, the computer displayed 35 mpg about halfway through and topped out at 35.4 mpg; that was the rating displayed as we exited the highway. The few miles more to the house saw that mileage drop quickly to 34.3 mpg.

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After 25 more miles of mixed suburban driving later that day and my 23-mile commute to work on Monday in bumper-to-bumper traffic, the computer showed 28.2 mpg. The 328i is rated 23 mpg city and 26 mpg combined.

But it's the highway mileage that is the question. If during my test the 328i couldn't break 35.4 mpg, perhaps the EPA was right to revise the number. But because it reached that number with some serious stress — winds, high speeds, added weight — I'm surprised the EPA didn't rate it higher than 33 mpg.

Comments 

Chris K

Not speaking to the 328's mileage, but my 2011 328's trip computer is optimistic. I can easily read >30mpg on a mostly highway trip and it reads 24mpg or so average in the city. When I fill up the car I've never gotten more than 30mpg and my city average is 22mpg. I'd say it's 2mpg optimistic on average.

My 05 Subaru was off too; for normal driving it would read 2mpg high at all times, and 4-6mpg high if I was driving for economy (damn turbo).

And my old 99 Grand Prix was comically bad. It would read a solid 28mpg for months at a time, but I averaged 22mpg. I think I hit 28mpg once on an interstate trip in Canada where I didn't have the guts to speed with my US plates.

My conclusion is that I've gotten really good at driving the gauges, but not as good at actually saving gas. :)

I find the little needle gauge showing instantaneous MPG more useful. It tells me when the engine stops fuel flow (coasting at low RPM above 20mph) and it makes it really obvious what the torque converter is doing, which IMHO is very important for getting decent mileage in an automatic.

In other news, the coolant temp gauge is back? I'm jealous!

Agent Mike

I am glad the EPA downgraded the mileage. BMW has taken a few "liberties" over the years. They needed to be brought back to reality.

Jonathan

35.4 real-world vs 33MPG EPA estimate?

Uh, no, that's an entirely reasonable gap. Even if you were cruising fast, I doubt you were driving aggressively with two kids in the car, revving up the engine.

I often break 34MPG highway on my 2009 Scion xB, which according to the EPA is only supposed to get 28MPG.

The real problem with the EPA numbers is the city MPG estimate. Every car can exceed its highway MPG because it's easy to just cruise, but no car gets its city MPG number when dealing with a bunch of red lights on a boulevard. City MPG estimates should be much less optimistic.

jaret

What Chris K said. The MPG readouts in cars are consistently off. They are typically optimistic. Use it as a refrence, but it is by no means accurate.

Jaret,
We've done a few stories on how trip computers are extremely accurate in a majority of today's cars. However, there's a chance some manufacturers may have more fluctuations. Perhaps BMW is one of them.

In my testing of cars it's rare that any in my hand for an entire tank of gas that the trip computer and fill-up calculations are off more than 10%. Usually they're right on the dot or within 1-3%

sheth

You cannot trust the trip computer unless you have compared it to your
observed mpg data. On top of that the 328i hasnt come CLOSE to matching
its EPA combined figures in any road test or comparison test thus far. IL,
MT and C&D have done comparison tests with the new 328i and I think the
HIGHEST average was 23mpg between those tests. MT was under 20mpg on their
test car. Even if you account for some aggressive driving that is WAY off
the EPA figure. This is the first evidence Ive seen that the new 328i has
any shot of achieving at least part of its EPA rating.

Julio

Other car magazines have said the same thing about mileage accuracy. So I believe what Dave says that the mileage at 35.4 mpg is accurate.

JohnInNJ

Don't use the trip computer or MPG display for mpg info. In most cars they are wildly optimistic. To get a proper MPG number, fill the tank, drive (n) miles, fill the tank again and note how many gallons of gas (g)the car takes during this refill. Then divide (n) by (g).

Lance

Nearly every car the "enthusiust" magazines test is way off the EPA estimates. They don't test drive them anywheres close to how the EPA tests them. Only a moron would think that someone driving a car through figure 8s, skid pads, and testing 0-60 and 1/4 mile times would be the equivalent to EPA testing.

I think Dave's testing was a lot closer to real world and EPA than the car magazines. I agree though that MPG computers in cars are usually a little optimistic and one tank of gas is not enough to measure them against as there can be too much flucuation in pump click-off and temperature expansion/contraction of the actual gasoline. A metered test in the gas line is probably the best and I think CR actually does that.

Chris K

Dave, perhaps the on-board MPG computer is more accurate for some drivers than others.

I coast a lot which would fill up the averages with lots of "infinity" entries. I suspect some cars are using better averaging algorithms than others.

Of course, BMW refuses make a speedometer that reads correctly (mine is off FOUR MPH), so why would someone expect their MPG gauge to be accurate?

Bob

I have to jump on the pile here. Unless you've verified its accuracy, you can't trust a trip computer's mileage figures....ESPECIALLY not when you plan to write an entire article based on its output.

Here's a piece we wrote in 2008 on the worth of trip computers and how gas pumps can be much less reliable.
http://blogs.cars.com/kickingtires/2008/05/mileage-blog-5.html

Yes, repeated fillups and long drives over time would paint a better picture, and owner groups may have the answer there. We have limited time to test the new cars in our fleet and we did make sure to say it was unscientific.

Chris K

With my old Pontiac (supercharged 3.8L) it was easy to throw the numbers off. Say your commute was five minutes of stop and go city driving, then 30 miles of highway driving.

If you reset the gauge pulling out of the garage you'd get a bunch of 18-20mpg readings followed by 28-30mpg readings for a half hour. Your final number would be somewhere around 22mpg. If you then repeated your commute for a week your number would stay around 22mpg.

If you waited until you were at highway cruising speed to reset the meter that first day, you'd get a half hour of 28-30mpg readings. If you then commuted the rest of the week your number would be closer to 26mpg.

That Pontiac greatly over-weighted early samples in its average. If you wanted to impress people all you had to do is reset the gauge before a two-hour highway trip. For the next couple months your MPG gauge would read 26-28mpg, which was hilarious to show off as you pulled smoky burnouts around town. :)

I'm sure some cars are accurate, and some off just slightly. But some of them should be ignored.

These days I use fuel logging with Fuelly. I rarely fill up my car unless it's at least half empty, so the pump-not-quite-full error is minimized by volume. Incidentally, I'm currently averaging 22.1mpg over 11907 miles with about 70% city driving (my estimate, not scientific). My cost per mile is $0.18 for 2012. My best fillup for 2012 was 28.3mpg, which was a 75mph Interstate cruise. If you've got a phone with a data connection, get Fuelly. It's fun for stats. :)

sheth

Even if we account for some aggressive driving, this car has come in WELL
under EPA averages in testing. At 65mph on the highway most cars can
achieve their EPA hwy figure, that doesn't mean 36mpg is what people can expect to see in realistic hwy driving. If you drive conservatively enough you can get EPA hwy mileage on ANY car. Im sure the EPA's analysis was just slightly more comprehensive than this isolated test.

Parrots

Ahem, sheth, Dave specifically said that there was fluctuations in the speed and that there was crosswinds and strong buffet ting, which is NOT good for aerodynamics. Kinda pay attention to what he says?

WTF

"unscientific real-world test"

QFT

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