I've been really focused on my mpg recently because I feel like it's getting worse. When I first bought my 08 last march I got 24-26 mpg just doing my weekly driving but now I am getting 19-21. I had an issue with my engine wiring harness a month ago that I got replaced under warranty and I was hoping that would fix my issue (maybe a poor signal from the MAF) but a month later and I am barely getting 250 miles per tank. Sometimes I drive for 15 miles and I swear I can watch my gas gauge drop a quarter of a tank. A guy at my work has an HHR w a 2.2L that gets 27-29 in the city. Why is the xB so horrendous? Could it be a failing sensor causing the bad MPG?

 

Did your spark plugs get replaced with the wiring harness?
If not, I would give them a look-see.

Have you tried pulling your MAF and cleaning it, or did the dealership after the W-H replacement?

 

No I have not changed the plugs and I'm not sure on the MAF. would this be expected at 36k? Is there anything else it could be?

 

I have no idea. I only brought those up because some others have had the wiring harness problem which can lead to fouled plugs, and a dirty MAF can affect gas mileage.

 

Okay I can report back now that I changed the plugs and cleaned the MAF. Seems to not have helped. In town I got 22 and then I just went on a road trip and averaged 23 on the highway going around 70 most of the time. If someone else says this is normal then I will accept that it's not some issue I am having.

 

Your mileage sucks. I get 26-27 mpg on freeway road trips (65-75mph) with heavier over-sized wheels & tires that have a high rolling resistance.

 

I didn't read through all the posts so forgive me if I am re-stating the obvious. Winter blend fuel is going to make a dramatic difference in fuel efficiency in the snow belt states as does your rate of travel. 40ish mph will make the best fuel mileage in a vehicle with this shape / size / power. The faster you are traveling over that, the worse off you will be when it comes to re-fueling.

I average 28 mpg during the summer months with a bike rack, and 24-25 in the winter without the rack. I set my cruise at 69 mph ( speed limit max is 65 here in Wi ) and drive about 350 miles a week on the freeway.

 

Alright, so mine sucks then. I've been tracking it since Oct and it's been consistent 21-22 since then. I have the oversized tires as well but I'm no where near 26-27. My tire pressure is within spec. Why would my 08 xB be so different than yours, Cionide?

 

Like pOrk said, it could be due to winter fuel (I don't think we get that here in sunny California), or it could be driving style. I believe your wheels are also a lot heavier than mine. I don't get 26-27 regularly, only on pure freeway trips. Normal driving for me is 90% freeway and 10% city, where my mileage drops to 24-25. Pure city I get less than 18mpg.

 

Nothing wrong with the car it's the fuel when they started selling ethanol fuel my fuel mileage dropped by 2 miles per gallon

 

I just got back from a long trip and averaged 22-23 mpg going around 72 mph the whole way. On my trip, i was in a big city with a lot of lights and there I got 17 mpg!!!

I am posting all of my fillup data going back to October. I got my wiring harness replaced (CEL lights were on) mid November and changed my plugs and cleaned my MAF mid-december. I also put in Techtron several fillups ago. My tire pressure is at recommended and my air filter is clean.

I ran into a guy with the same xB as mine (RS 5) and his is stock like mine except he has the standard wheel package instead of the 19" TDRs like I have. He said he gets 29 pretty regularly but he commutes about 45 minutes to and from work each day.

Considering his as a baseline (drives in same state with same winter fuel blend and i just did a lot of hwy driving) do i have an issue or is there anyway that my wheels can be dropping my mpg by 6-7?

EDIT: I just read on clubxb.com that the stock tire and wheel combo weighs 41 lbs per wheel and the 19" TRD's tire and wheel weigh 31.5 lbs so I'm thinking this is NOT my issue. If anything I should be better than stock.

I have yet to change the fuel filter. It could be the original with 40k on it and I plan to do that today

EDIT: Advanced just told me that the fuel filter is in-line with the fuel pump and therefore not serviceable like it was on my old honda civic.

If I take it to the stealership, what can they check/change/replace for me that would make it worth their $100/hour rate. What about getting the injectors cleaned? Am I freaking out over nothing?

 

I have a 2008 Scion xB AT with Strup Header and TRD Cold-Air Intake, 55k miles.

Bold One: The lights always kill you. My city is the largest in the U.S. land-wise, and in certain parts, there's tons of lights that will devastate my MPG. Try coasting more and tapping your brake less. When I'm feeling conservative, I drive this way.

Bold Two: The problem is this other guy is commuting 45 minutes, and is most likely driving on freeways and interstates more than you are. Not to mention, probably doing a safer speed. When I used to commute the same for my job, I coasted on I-95 at 66mph and achieved impressive fuel economy. Since I don't have that commute anymore, my mileage went down because I'm not on the freeway.

Bold Three: You definitely have the right to be concerned, because I lost a lot of my fuel efficiency, but most of it is because I have that header in now.

For my circumstances, I drive 80% city/20% highway. My average is around 23-25. It used to be in the 26-27 before my header was installed. I'm not as concerned with this slight drop because now that I have that speed gain, I can accelerate faster and avoid bad drivers in particular circumstances (which is common in Florida).

As for your 18mpg city, I'm not sure what that's about because I never get that low. I can only suspect that it's your driving habits causing that. There are times when I am for spirited driving, but when I'm in the city, I'm always coasting or cruising. I try not to ever hit my brakes unless I am forced to.

The best way to do this is to stop acting like you're in a hurry, because I've learned that saving a measly 2 seconds is meaningless. So I gap myself at least 1.5 cars away from people when I'm following. This allows me the opportunity to coast more rather than tapping on my brakes and losing momentum.

 

Thanks for the input. I hear what you are saying on the driving habits. but i definitely feel this is not what is causing my issue. I use cruise control when I can and I also try to avoid excessive breaking. In fact, now that I have been monitoring my mpg regularly, I would say I am babying it even more. But this is where my concern is coming from, I've owned this car for a year and a half now and have just recently noticed this decline in my fuel economy. My driving habits haven't changed enough to justify this large of a drop in mpg.

What I am looking for is what could be causing this mechanically. I am hoping someone will chime in who has had a similar issue and can recommend what I should tell the dealership to check for. I can't help but feel this is all related to my engine wiring harness which went bad and had to be replaced. But I can't figure what has been affected and could be causing this.

 

I doubt that it's your engine wiring harness. Just to be sure, you might want to reset your car by taking the negative and positive terminals off your battery for at least 30 minutes. Did you check all your filters (not the cabin one, but the oil filter and airbox filter)? Dirty filters affect fuel economy.

The only other things I can think of are fuel injectors needing to be cleaned (I know, unlikely at the age of your car, but probable) and tires (albeit improper inflation, or camber issues insofar as cupping, etc). I just have a big feeling that it's your tires. They're probably inflated fine, but maybe you have uneven tire wear that you're not aware of that could be affecting your performance.

Sorry, but I'm all out of ideas at this point.

 

That ain't it... I have Falken 912's that are 245/40-18 on the rear with 35k miles on them and severe cupping due to no tire rotation (staggered). The tread is barely worn (except for the inside cupping), and I just got 28mpg calculated on my last tank of gas. Front tires are 225/45-17 and extremely worn, ready for replacement soon. My rear wheel bearings were shot and replaced 10 days ago. I'll be watching the mpg, as my last tank was about 3mpg higher than before the bearing replacement.

 

Were your bearings making noise? Is that how you knew they were shot? I did get 2 new tires in October along with a shim kit that had to be installed on the rear to bring my alignment into spec after lowering my ride. But this change brought my alignment in spec so I would think I would see an improvement. Maybe there is something screwy going on there?

 

Yes, the bearings were making kind of a whining/howling noise that became higher pitched as speed increased while under acceleration. The noise would greatly subside when I took my foot off the gas pedal.

 

I'm proposing this MPG reduction based on my previous vehicle before my Scion, a '94 Acura Legend. When I had a major wheel bearing problem as well as extreme tire wear, my MPG on my trip computer was terrible, and when I hand calculated, it was horrendous. Naturally, that V6 Acura had about 18mpg city, but it dipped to around 13. I remember how disappointing that was.


EDIT: I just looked at my trip computer for my xB today after filling up and my average MPG is 20mpg. I drive about 90% city, 10% highway nowadays and am flabbergasted at this pitiful result. I'm very much tempted to relinquish my Strup Header just to gain back a few MPG's.

So... I might be selling a Strup Header soon. lol

 

Sounds like you are close to me and I don't have the header.

I have been manually calculating mine every tank but for the first time yesterday, I reset the average mpg on the dash with about a quarter of a tank left. After only a few minutes, 22.1 popped up on the display and for the rest of the day I was between 22.5 and 20 as it kept recalculating. To me this indicates it is not some wheel issue as it popped up so quickly and was pretty close to what I have been averaging over a full tank. Of course I was going through lights and in traffic so I am going to head out to the freeway and see what pops up when I do this at highway speed.

CIONIDE-you report 29 on the highway. Is this over a full tank with it all highway miles, like only one acceleration up to speed? I am trying to collect as much data as I can so I can report all this to the dealer.

 

I've only seen 29mpg a couple times, on absolutely pure freeway runs from NorCal to SoCal. As I stated earlier: