Bad Gas Mileage

August 18, 2005 12:53 PM

Why is my Outback only getting 21 MPG!

I recently bought a new Subaru Outback wagon that is rated for 23 mpg in the city and 28 mpg on the Hwy. I recently took it on a road trip and was not very pleased with the mpg I was getting. Both city and interstate driving were hovering around 21 mpg. I talked with the dealer and they had two things to say. One it is a new car and it takes time to “break-in” the engine to see expected results. And two, occasionally “flooring” it to get the rpm’s up will help break in the engine and clean out built up carbon etc.

My questions are, how long do I put up with this below expected gas mileage, is there anything I/or the dealership can do about it, and is “flooring” and driving it hard occasionally good for the engine?

Side notes, the car was moderately loaded (two suitcases and camping gear for two) and I had two bikes mounted on the roof (I know this would add some drag, but didn’t think it would be a noticeable difference.)

My previous car was an 95 Subaru Legacy Brighton, I was used to getting 24/30 mpg with it. It had a similar but smaller engine

Thanks!

posted by retro88 to travel & transportation (24 comments total)

I thought that "flooring" a new engine is a bad thing, and that you should never really juice an engine until at least 500-1000 miles or so.
posted by rxrfrx at 12:57 PM on August 18, 2005

The bikes add a lot of drag and loads, however small you think camping gear might be - it's probably not, also add to the problem of low MPG

My Civic is rated for 28 I think and I've gotten as little as 23 and as high as 44! so much depends on the driver, the load, the drag.
posted by FlamingBore at 1:00 PM on August 18, 2005

I understand that even empty roof racks can affect mileage, so I'm not surprised that bikes would cause that much of a decrease. I know that carrying a canoe on top of my truck caused about a 5 mpg decrease.
posted by MrMoonPie at 1:04 PM on August 18, 2005

Fuel economy ratings are based on 40-year-old standardized tests that don't really simulate how people drive their cars today. Car manufacturers probably design their cars to have the best gas mileage under testing conditions, so the actual gas mileage drops off when you go over the test speeds. This article has some more reasons.
posted by driveler at 1:04 PM on August 18, 2005

'The test to determine the highway fuel economy estimate....simulates a 10-mile trip and averages 48 mph. The maximum speed is 60 mph.' Hardly typical of contemporary highway driving.
posted by driveler at 1:06 PM on August 18, 2005

I'd bet those bikes added a lot of drag and drag can have a dramatic effect on mileage. That's why your city and highway mileage were similar. I get significantly better mileage on the highway in my pickup just by leaving the tailgate down.
posted by tiny purple fishes at 1:08 PM on August 18, 2005

Generally speaking, a new engine is supposed to have a "break in period." In many cases you AREN'T supposed to "floor it" during this time. For example, a new Mini Cooper's break in period is 1000 miles, during which time you're supposed to keep the engine below 4k rpm, I believe.

Added weight and drag on the roof would easily bring your mileage from 28 to 21 mpg. So would stomping the gas a lot, etc. Drive conservatively and you'll get noticeably better mileage. Just look at the forums for people who drive hybrid cars. There are a million and one driving tips to help you squeeze a tiny bit more mileage out of every drop.
posted by autojack at 1:08 PM on August 18, 2005

According to this page, break-in happens mostly in the first 100 miles, and it is important to run the engine hard during the break-in period -- but make sure the engine is warmed up before you do this!
posted by mbrubeck at 1:09 PM on August 18, 2005

Your owner's manual should detail the break-in procedure.

I've seen in auto magazines that they find gas mileage generally gets better over the first 10 to 20 thousand miles. If you don't have that many miles yet, maybe you shouldn't be too concerned.

Also, check the regular tune-up stuff to make sure something isn't causing a problem. Spark plugs, air filter, fuel filter. Make sure you're running the right oil viscoscity for your car and the weather conditions in your region (see owner's manual).
posted by knave at 1:18 PM on August 18, 2005

I doubt the dealer or Subaru will do anything about your mileage, so it's up to you to improve it, or dump the car. There are a few major differences between your Outback and your old Sube. First, as you've noted the engine is now larger, 2.5l vs. the Brighton's 2.0l. Second, your new car is marginally larger, but I suspect much heavier and rides higher off the ground. All of these changes can result in reduced mileage. I had a '95 Legacy wagon, and I averaged between 23 and 26 mpg, so indeed, Your Mileage May Vary.

I believe that the extra weight and drag created by the bikes could have contributed to a 2 to 3 mpg penalty. Have you checked your tire pressure? It's been proven that having your tires mis-inflated is one of the major factors of poor fuel mileage. Make sure your pressure equals the number specified by Subaru. You should be able to find this on the driver's door jamb.

How fast were you driving on vacation? If you were going in excess of 65, that will definitely cut your mileage. I now drive a Forester, which has the same engine as your car, but is a bit lighter. On my normal commute, which is roughly 30 miles one way I average 24-25 mpg and most of it turnpike driving at 70 mph. We recently took weekend trip out of state, and because we were on secondary roads my speed averaged closer to 50 mph. I was pleasantly surprised to see my mileage go up to 33.

Your mileage should go up a bit once the engine is broken in. Whoever told you it's a good idea to floor your engine is full of crap. At best this will make your mileage worse, and you can potentially damage your engine if it isn't sufficiently warmed up when you try this. In other words, NOT a good idea.
posted by SteveInMaine at 1:20 PM on August 18, 2005

It's the bikes. Take a trip with the bikes then without. It'll show you the difference.
posted by puke & cry at 1:25 PM on August 18, 2005

I have a Jeep Grand Cherokee (17mpg, I have Saudi friends...) and know people to raise their gas mileage a lot by lowering it a few inches. You might try that but if it's money you're saving, replacement springs might take several years to pay off the 2-3mpg difference.
posted by geoff. at 1:36 PM on August 18, 2005

I have a couple Subarus, and I have found that after a few thousand miles, the mileage improves a little. It's not the engine that needs to be broken in, though. It's the computer. It will adjust itself to your driving habits, and that improves the mileage somewhat.

A bad tank of gas (resulting in an engine knock) could make the computer conservative, lowering your mileage. If you suspect this happened, you could try an ECU reset. (You can find out how online.) This is probably not the case if your car is new.

Another thing you might want to check is that the tires are properly inflated (see the sticker inside the driver's door).

I assume that you're certain you reset the trip meter when you got the last tank of gas you drove with (and not later), that that tank was filled completely, and that you're figuring your mileage by hand rather than by a digital display.
posted by landtuna at 1:47 PM on August 18, 2005

Another data point in favor of the racks and drag: Click and Clack had a call not long ago from a hybrid driver whose mileage plummeted when he had the bikes on the back rack. He even drove the same route with and without to test the difference. It was huge. Their conclusion is that the difference in drag was enough to make the hybrid keep the engine on all the time.
posted by phearlez at 1:59 PM on August 18, 2005

21 mpg to the gallon sounds pretty good to me with two bikes on top. That is a fair bit better mileage than I get with my 2003 Legacy L when I am driving with 2 bikes on top. A fairing on the front of the roof rack will improve your mileage somewhat. I recommend putting the bikes inside. They will fit in the back with the seats folded down and you do not even need to take the wheels off. Just place a blanket between them. Easier on the bikes (no bug splatter), and your pocket book.
posted by xcwhite at 2:35 PM on August 18, 2005

Two bikes makes a huge difference. We we travel with our tandem on the roof rack of our 6 cylinder Outback we see a 20% difference. Single bikes go inside if possible, but the tandem is just too big and we're usually going somewhere sorta far like for vacation.
posted by fixedgear at 2:42 PM on August 18, 2005

I'll add the reference point, that my manual '04 WRX wagon gets an average of 24 MPG with me driving it. I tend to keep it above 3K RPM's while crusing, which is awful for fuel efficency (turbo is causing it to dump fuel on). It's seen a best of 38 MPG over an 1100 mile road trip, with a signifigantly more conservative driver behind the wheel.

My friend's '05 Outback, with a 2.5L non-turbo engine, a manual trans. and around 10k miles gets an average of 25 MPG. I agree with the general consensus, the bike rack w/ bikes could easily shave 2-4 MPG off at highway speeds. Try removing it, and taking some longer highway trips.

Really though, that car will never realistically average over 26 MPG in normal conditions. And assuming 12K miles a year, and $2.50 a gallon gas, the current inefficency (with bikes) is costing about $275 a year.

Most of the initial break-in period for a new car occurs within the first 100 miles or so. The engine mechanicals honestly doesn't care much after that (though today's trainable ECUs might). A 5000 mile 'break-in period is mostly the auto manufacturer trying to teach you to be gentle with the car. Gentle driving == fewer warrenty claims == deniability if you drive the car normally and something does go wrong.
posted by zeypher at 4:06 PM on August 18, 2005

How fast do you drive on the highway? Drag goes with the square of the velocity and those bikes are certainly adding drag.
posted by jduckles at 6:54 PM on August 18, 2005

"How fast do you drive on the highway?"

A more pertinent question might be "How quickly do you accelerate to freeway speeds?" The difference in fuel mileage between the most efficient freeway cruising speed and 75mph is likely less than the difference in accelerating from 0-75 in 15 seconds vs. accelerating from 0-75 in 30 seconds.

Also, treat your gas pedal and brake pedal like they're sitting on eggs (accelerate slowly unless required to merge, brake gently and try to avoid braking at all by planning ahead) and you'll see a marked increase in overall mileage.

Additionally, the Outback has wider, more aggressive tires than a standard Subaru, and increased rolling resistance due to wider tires is a factor in increased fuel consumption.
posted by mr_crash_davis at 8:19 PM on August 18, 2005

The EPA has a rule of thumb: "Each 5 mph you drive over 60 mph is like paying an additional $0.15 per gallon for gas." Or, to put it in more helpful terms, there's a 7-23% benefit by keeping your speed down.

Also, "An extra 100 pounds in your vehicle could reduce your MPG by up to 2%"

And "Aggressive driving (speeding, rapid acceleration and braking) wastes gas. It can lower your gas mileage by 33 percent at highway speeds and by 5 percent around town."

Throw in the aerodynamic drag from the bikes, and I think you have your answer.
posted by pmurray63 at 9:03 PM on August 18, 2005

Your mileage doesn't sound that bad considering the drag. It might improve a couple of mpg after the engine breaks in some more and the computer adjusts to your driving style, the local weather and the gas you tend to use.

My 2001 Outback VDC (3.0l H6, 4 speed EAT, 132k miles, stock rack crossbars only) gets me anywhere from 22 mpg (when I'm in serious speed mode -- 85-90 mph) to 24 mpg (55-65 mph). When I was commuting regularly with 50% of my hours in stop-and-go traffic most of the time the mpg was closer to 19-21.

When I run with bikes I keep them on a tailgate rack and that doesn't affect the mileage more than 1 mpg. I would expect keeping them on the roof to at least double that effect.

The best mileage I've gotten was on a trip over slow two-lane roads averaging 27 mpg at a pretty consistent 45 mph.

As my VDC is EPA-rated for 27 mpg on the highway and I've never gotten close to that (except for that one long, slow ride) I suspect Subaru engineers the cars to do very well on the EPA test but not so well on the Opposite George test. Previous experience with my 1996 Outback (2.2 liter 4-banger w/stick) -- which consistently clocked in about 2 to 5 fewer mpg than the EPA rating -- strengthens my belief.

My mileage drops pretty significantly during major snow storms (sub-20), but I think that's a combination of me pushing it hard in the snow and tending to idle it a lot while clearing it off or waiting for traffic to get going again (CT loves to platoon snowplows which can mean stopping for a while until they get it together.)

I don't know which transmission you have but the VDC pushes power to all 4 wheels all the time (35/65 front/back split) which eats up mpg. If you have the stick I think it also splits the power all the time. Some Subaru automatics (used to?) basically operate in FWD unless the front was slipping (90/10 split w/that 10% coming from residual drag) and I believe their mileage was quite a bit better and closer to what you were getting with the Brighton (a FWD model, no?)

Also keep in mind the Outback is a HEAVY car (mine is almost 2 tons, yours probably heavier than mine). Since this is almost twice the size of the Subarus when I was growing up, I have to keep reminding myself that I'm not driving a pretty average-sized car and not to expect sub-compact mileage!
posted by Opposite George at 12:41 AM on August 19, 2005

Drive slower. I just saw a local news report last night that demostrated the difference in MPG between driving 55 and 65 to be 13%.
posted by poppo at 5:26 AM on August 19, 2005

I have never had a car that achieved it's 'official' MPG. Those numbers are for ideal conditions only, and have little to do with reality.
posted by eas98 at 7:22 AM on August 19, 2005

Just to counter eas98, I often achieve *more* than the official EPA highway estimate in my car (a 2002 Audi AT 1.8t, which I suspect is tuned for better mileage at higher ranges than the 49 mph test level in the US). So much depends on how the car is driven.

Also, one more nod in obviousness toward the bicycles wrecking your mileage. Even rolling the windows down can inhibit mpg.
posted by werty at 8:18 AM on August 19, 2005