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Reduced highway mpg in a 1-year-old car. What gives?
June 2, 2014 12:27 PM   Subscribe

2013 Subaru Crosstrek XV got 32-33 highway mpg last year. Now it gets 28.

I bought a new 2013 Subaru Crosstrek XV last year, and have put 10,000 miles on it. Last May I took an Iowa-Ohio trip and got 32-33 highway mpg. Just last week doing pretty much the same trip I got 28 mpg. I've measured this both with the onboard computer and just pen-and-pencil figuring.

I first noticed lower mpg (22/28 city/highway) on a trip in November, and was told then by the Subaru dealership that this drop is probably due to a combination of winter gas blend and cold weather. I expected that to change with the non-winter blend gas. Since April or so, my city mpg have gone up to what they were before; highway mpg have not.

The check engine light isn't on, the tires and brake pads haven't been changed, I drive the same way and use the same gas stations, and my tires are full of air. The only things I've done to the car were a camber alignment a few days after I got it, and one oil change in early November.

I did take a high-altitude trip in March. Could something about that trip (the high altitude itself, or maybe revving a little hard trying to climb hills at altitude) have done something to my car?

I called my Subaru dealer and was basically told that in the absence of a check engine light, there's really nothing they can do to investigate or fix anything. This was frustrating and uncomforting.


1. Am I right to be worried, or do new cars normally show this decline in mpg?

2. If the mpg drop is abnormal, what should my next steps be to diagnose or fix the problem?


This car is my baby, I have little mechanical knowledge, and I'm kind of freaking out that I've somehow hurt her or busted the head gasket or something, so any answers would be great. Thanks, MeFi!
posted by nicodine to Travel & Transportation (20 answers total) 3 users marked this as a favorite
 
Are your tires at the correct PSI? Under-inflated tires will sap 2-3MPG.

edit: sorry, missed this the first readthrough.
posted by zug at 12:40 PM on June 2


1. No, a car this new shouldn't be showing any noticeable signs of decreased mpg at 10k.

2. Do you have any signs of uneven tire wear? Is your steering wheel perfectly centered when you're going straight? Any steering wobbles or noticeable pulling in one direction or another at speed? It's possible the camber alignment was goofed, and misalignment can induce drag which could well result in this sort of mpg hit.

I'm also a little surprised that you got/needed a realignment at ~10k miles on a brand new car. What precipitated that repair?
posted by stenseng at 12:40 PM on June 2


Your car is almost certainly fine. If your city MPGs are close to normal, than one long trip doesn't a crisis make.

It is true that MPGs will diminish with winter blend - I usually go from 17-18 to 13-14 in my truck, so it can be substantial. High altitude doesn't hurt engines - hell, the V8 Toyota makes for the Tundra and Land Cruiser is also used in airplanes.

Things I would look at on your car - change the air filter, and grease all the zerks really well. Make sure your tires are inflated correctly - or even a bit overinflated. Also, make sure that you are running the correct octane fuel - my Tacoma requires 91+ and runs like crap on less than that. It is worth mention that some places use ethanol, which isn't in and of itself bad, but it does go stale and results in reduced performance.

You can also check that your brakes are properly adjusted and not hanging up - I had a pad come loose and just wedge up in between the rotor and the caliper. Or that a piece of molding or trim under the car isn't flapping in the wind.

Highway MPGs have a few factors external to the car - wind, relative humidity and other traffic. I get better MPGs when there is moderate traffic because there is always somebody breaking wind for me.

But other than that, I wouldn't worry too much about it - you don't have a statistically large enough sample to know for sure that there is a major problem, and no other symptoms either.
posted by Pogo_Fuzzybutt at 12:44 PM on June 2


Also, I think your dealership (or at least the person you spoke with) was blowing you off. There are a number of diagnostics that can be done on new cars via OBD2 codes etc., that might theoretically shed light on the situation. The "idiot lights" are not necessary for a diagnosis.

Further, you should still be in somewhat of a "honeymoon period" with the dealer, having just recently purchased a brand new car. A reputable dealer should be more willing to check things out for you than it sounds like this one was. I'd recommend talking to supervisor(s) till you can get someone who will take an interest in providing some customer service.
posted by stenseng at 12:47 PM on June 2


Was it warmer than last time, such that you used more air conditioning or drove with the windows open more?
posted by jacquilynne at 12:47 PM on June 2 [1 favorite]


I have noticed improvements in mileage after an oil change — you might, as well.

But I'm surprised that you have only done one oil change on a new car that you've already put 10K on. Usually, with a new car you're supposed to do a couple oil changes in the first 5K: one at around 1K and a second at 5K. Then another oil change each 5K, if you're using synthetic, and 3K if you're using conventional oil.

All else the same, you might well void the engine part of your car's warranty, if you don't do regular service. I'd take it in for an oil change, at least, and see if you get better mpg.
posted by Blazecock Pileon at 1:00 PM on June 2


I have a 2012 Mini Cooper, bought new, never noticed any change in MPG through the two years I've had her, except for it falls about 3 mpg hwy due to streamlining issues (ie when I have my roof rack on versus off). Did you add anything cosmetic to the car between those two highway trips that might affect air flow over the vehicle?
posted by danapiper at 1:15 PM on June 2


Frankly, modern oil can last a lot longer than most folks are aware of, and in a brand new car with this low mileage, without some catastrophic event like a serious oil loss or overheating, you literally couldn't have oil old enough or worn enough to more than negligibly impact fuel economy.

Under the best of circumstances, in high mileage engines, an oil change might give you a 1-2% econ boost, but that's about it. This isn't an oil change issue.

You've either got a problem with your fuel/air/spark calibration, (sensor malfunction, computer problem, clogged air filter, fuel injector problem, etc.) or you've got a mechanical drag issue, be it aerodynamics, hanging brakes, or toe-in or other misalignment inducing drag at the tires.

NB: this is all other things being equal - same gas you previously used, roughly same driving patterns, same location, altitude, etc., same use of AC...
posted by stenseng at 1:15 PM on June 2 [5 favorites]


Going uphill with a small engine will sap your MPG in a hurry. I took a Corolla through the mountains of WV (all interstate) and easily lost 5 mpg on that trip. Then add in 1 mpg for a dirty air filter, possibly 2 more from under inflated tires, etc and you can lose 5-8 mpg quickly.

Highway mpg is driving on flat roads, without a significant headwind, maintaining 60 mph all the time. If you are off highway even 20% of the trip, you'll see a corresponding dip in mpg. The numbers are guidelines, not gospel.

Also, "This car is my baby, I have little mechanical knowledge" don't go together. If you care that much about the car you owe it to yourself and your baby get more knowledgable about how cars work, and how to maintain them.
posted by COD at 1:38 PM on June 2


Really, it could have been windier, warmer (putting more stress on AC), traffic could have been a notch heavier all the way or tied up a few places it wasn't tied up on the previous trip. It takes only a few factors to lower your mileage significantly.

I would try a new tank of gas and take a flat 3 hour drive with the AC off, making a point of featherfooting it as much as possible. The golden ideals of maximizing your mileage are a) never brake if you don't have to and b) maintain consistent speed with enough following distance that you can slow down instead of braking when traffic bunches up suddenly and resume your speed with some momentum. Leave the AC off and the windows closed as much as you can stand it. See what you can get as a *maximum* mpg (without resorting to the advanced tricks, some of which are somewhat risky or illegal, like coasting for long downgrades or drafting behind trucks).

Have you changed the amount of weight you are carrying in the vehicle? Were you alone one time and with a passenger the other, or do you keep road salt or something in back that wasn't there before?

I too wonder about the camber alignment "a few days" after picking up a new car. Did the dealer explain how it got out of whack?
posted by spitbull at 2:25 PM on June 2


Traffic could have also been 5 mph *faster* on average. Every notch above about 60 comes a price.
posted by spitbull at 2:26 PM on June 2


Oh and if you can't reproduce your best previous mileage by attending closely to maximizing it, then print out stenseng's answer and show it to your dealer. By the time the light comes on, some problems have been developing for a while.
posted by spitbull at 2:32 PM on June 2


Does the Crosstrek have the fold away luggage rack bars like the Outbacks do? If so, were the bars not folded away on the lower mpg trip? It could make a difference.
posted by smalls at 3:05 PM on June 2


I don't have much to add to answer your question, except that I am also the owner of a 2013 Crosstrek, and just last week was wondering about the fuel efficiency, too! I don't have any data to shore up my *feeling* that efficiency was dropping off (e.g. it's possible I've been doing more around-town driving), but your question certainly resonates with me. Maybe I should keep a log of type of driving and distance and see if I can find any patterns... Hm.
posted by absquatulate at 3:10 PM on June 2


Thanks for the helpful answers so far, all!

I go 70-80 mph on interstate, and I try to maximize mpg within that range, which is how I was able to originally reach 32-33 mpg (the EPA max estimate for the car). Again, same driver, same trip, same small amount of cargo/addons, same time of year (so presumably same temps, and I go easy on the AC), etc. I have done other long trips, but have only been recently alarmed that my highway mpg on these trips remains low after the winter. I presented only these two comparison trips because they were basically identical - save for the mpg.


On oil changes: manual said to do the first at 3500 miles, so I did. I am indeed behind schedule and should have done my next one at around 7500, so I got an oil change today (just picked the car up); brakes appear fine, they said. I will be very surprised if mpg improves for the rest of this tank of gas after this oil change, but I will update if it does.


I'm also a little surprised that you got/needed a realignment at ~10k miles on a brand new car. What precipitated that repair?

I test drove a different Crosstrek and ordered one with different options. When I first drove the car I purchased (foolishly, I only drove it after signing paperwork) it noticeably pulled to the side. I took it in, apparently it had exited the factory out of spec: the left rear tire had a "toe" (?) of 0.33 deg and was changed to 0.15 to be within spec of 0.00 to 0.24. Currently it continues to feel to drive well (i.e., goes in a straight line), but it is quite possible that the issue is now causing a different problem.


So far I figure the dealership blew me off because I'm above the 10k mark. Or because it was 8am, who knows. stenseng, your comment quite nicely and very specifically backs up my concerns. I guess I'll just call the dealer back, use sharper and more specific words, and keep demanding to speak to different people until I get someone more responsive.


This has all been extremely helpful and validating so far, and I welcome further thoughts. I'll definitely keep reading this and marking more "best answers" as I go! Thanks in advance.
posted by nicodine at 3:24 PM on June 2


Huh. I find it odd that the car could have passed inspection from the factory with the alignment out... At very least, I'd have the dealership recheck the alignment...
posted by stenseng at 3:56 PM on June 2


On oil changes: manual said to do the first at 3500 miles, so I did. I am indeed behind schedule and should have done my next one at around 7500, so I got an oil change today (just picked the car up); brakes appear fine, they said. I will be very surprised if mpg improves for the rest of this tank of gas after this oil change, but I will update if it does.

mmmm, does the date of the oil change coincide at all with the difference in mileage? The oil isn't getting dirty enough on this interval to matter, but if they put in the wrong viscosity (entirely possible if you went to Jiffy lube or some such)it can cause this kind of problem.

Check also your air cleaner box, it is really unlikely it has gotten dirty enough to screw up the mileage at 10k, but you never know (and sometimes you will find a squirrels nut stash in there...)

Also check the oil levels in the differential on the rear. With the AWD system you can get some weird drag issues if something isn't right and the alignment being out of spec on a new car is a little worrisome that something that messed up during shipping (are the crosstreks made in Japan or US?). I had a problem with part of the emissions control in a brand new Juke that was causing a vacuum problem, turned out it got broken during assembly, they eventually found it, but it took a while and my mileage went up about 5-10% when it was fixed. I was also getting a check engine light on that part, and anything that being so far out of spec to cause this would likely throw an engine light (not certainly, but likely).
posted by bartonlong at 4:41 PM on June 2



Huh. I find it odd that the car could have passed inspection from the factory with the alignment out... At very least, I'd have the dealership recheck the alignment...


It is not at all uncommon for the transport guys to screw up when strapping the car on the trailer or something and messing up the alignment. My Tacoma had an alignment issue when I bought it at 7 miles on the clock and they fixed that while they were detailing it for purchase. of course, I offroad it, so the alignment has been (re)done about 10 times since then.
posted by Pogo_Fuzzybutt at 10:20 AM on June 3


So the bad news is, I'm a doofus, and the good news is that the oil change seems to have cleared everything up! City and highway mpg are spectacular once again. I was quite surprised. Lesson learned: double- and triple-check that manual to get the timing on the first and second oil changes right.

Thanks again, MeFi.
posted by nicodine at 10:23 AM on June 6 [1 favorite]


Yeah, I still don't think there's any way that an oil change, in and of itself, resulted in this kind of a mpg difference. I'm guessing it was some sort of ancillary service at the time of the oil change - air filter replacement, correct pressurization of your tires, *something*...
posted by stenseng at 2:12 PM on June 9


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