Gas Mileage Drop

[hcsem]

I've got a Vibe base with manual transmission. 23,000 miles in 8 months and climbing fast.I had consistently been pulling 35-37 mpg for about the first 4 months, then it dropped to more like 25-27 for no clear reason. I travel a fair amount, and rarely put gas in at the same station twice in a row.Just had it in at the dealer and they insist nothing is wrong. Big disappointment for right now, I loved getting 35-37 mpg.Any suggestions?Thanks.

[DavidPIL]

hiya...It's normal for mileage to go down in the WInter. Looks like you're in Minnesota so I'd have to assume it's down right brrrrr up there. Most cold weather states refomulate the gas in Winter, I'm also assuming again but I think it's to keep emisions down because of a variety of factors. I try to run a gasoline that doesn't add ethanol (10% added around here usually). You also have to take into account the temperature on the mechanical parts of the car and the oils and greases. Until these warm up, they are a bit thicker due to the temperatures. This could cause a bit more drag in the parts. Again, I'm assuming all this because I'm not a mechanic. It all seems logical to me though.Also, most people tend to let the vehicle warm-up a bit longer as it gets colder. This won't eat up a lot of gas but it will be one of the many factors causing the mpg to go down. Also some people tend to run the defrosters a bit more which again takes up some juice.I was getting anywhere from 31-33 mpg but now I'm lucky to get 26. It's seasonal. It's always happened to me so it's expected. It hasn't been too cold here in Illinois yet but I can imagine the mpg will go down even further as the temps drop.Once again, I'm assuming but it seems to be normal. Oh, you might want to check your tire pressure, as the temps go down the pressure drops in the tires. From what I've read, about 1 lb per 10 degrees or so. Lower tire air pressure can also cause a lowering of the mpg.Dave

[pmh013]

I'd blame it on the cold weather, too, as long as everything else is operating normally.In the summer, I get about 8L/100 km. In the winter, I get about 9L/100 km. Sorry, I'm feeling just too lasy to to the coversion right now. But I'd think that a 10% fluctuation between summer & winter is acceptable.As a side note, if you don't have a regular station, at least try to keep to a "main stream" one. I used a cheap no-name station as my regular station, and their crappy gas plugged up my car.

[joatmon]

If you had it for 8 months, and the gas mileage dropped 4 months ago, that would be August/September, so cold weather factors probably aren't responsible. Have you noticed any drop in performance/power or driving habits?Check out pmh013's ordeal, a major runaround from the dealer, wierd shifting behavior, mpg drop by 1/3 turned out to be a catalytic converter problem, no error codes in the car's computer. http://forums.genvibe.com/zerothread?id=2894Not saying it is the same problem, but it sure doesn't sound right to drop 10 mpg.

[Raven]

Quote, originally posted by pmh013 ».As a side note, if you don't have a regular station, at least try to keep to a "main stream" one. I used a cheap no-name station as my regular station, and their crappy gas plugged up my car. On many occasions I have seen the refueling truck in my neighborhood first filling the SHELL station and then crossing the bridge to fill up the "cheap no-name station" from the same tanker of fuel. For years I have heard tales of bad gas from "discount" and little-guy gas stations. There are not that many producers of gasoline and all stations, big and small are supplied with almost the same quality of fuel.

[pmh013]

Quote, originally posted by Sunny » On many occasions I have seen the refueling truck in my neighborhood first filling the SHELL station and then crossing the bridge to fill up the "cheap no-name station" from the same tanker of fuel. For years I have heard tales of bad gas from "discount" and little-guy gas stations. There are not that many producers of gasoline and all stations, big and small are supplied with almost the same quality of fuel. I only wish the Shell truck was refilling this station. They were basically buying whatever they could get their hands on. I'd seen several different trucks (none of them branded) fill up the tanks there. I know that the Shell & Petro-Canada stations around here all get their gas from the Co-op refinery, because it's the closest one for 500 km or more. But, I used to get 75% of my gas from that one station, and my car was majorly bunged up. Haven't gone back, and I've since gone 40,000 km with no troubles. As a side note, the station is now closed down!

[DavidPIL]

(this is actually to all who are posting here and not just to one person in partucular)Hello...I have always been told don't go to a gas station where the tanker is or has just filled their reservoir. Stirs up sediments in the tank. You could have run into a situation like that though I've heard the filters at the pump take care of that pretty much. Now, if the filter is bad or clogged, who knows. Just steer away from that. Here I used to see a McDaniels tanker fill a Clark gas station then would see a McDaniels at a Speedway and Shell. The odd thing about that is the octane rating from Clark to Speedway is different. For premium, that is.Some stations combine Premium with Regular to get a mid-grade, others have 3 separate tanks. The 2 different types of stations might get their gas from the same place but the way they're mixed might yield a variation in octane. I dunno... I just don't think all gas is the same.. or at least not from station to station.I was told when searching for my Vibe that the name brand companies take from the top of the reservoir (tank) and the off-brands take the bottom. Someone mentioned they saw a tanker at a Shell then go over to an off-brand station. I would think that would be taking from the bottom of the tank. Sediments and such could possibly get into the stations tanks if they get the last fill. Kinda like how it's bad to let the gas in your vehicle get much below the last quarter or so. Well, I don't know this for any fact but it does seem to make sense.I promise you that I get better mileage in the Summer than Winter and I get better throttle response and mileage on higher Octane Marathon w/o Ethanol than 92 octane with Ethanol... But no matter what I do I get a drop of about 10-20% mpg in the Winter as compared to Summer. He's in Minnesota, It could get cold in Minnesota in Sept... They may change the gas formulation up there earlier. I just don't think it's a big issue unless it was a lot lower... 1/3rd lower would make me very concerned.Dave

[joatmon]

his mileage dropped from about 36 to about 26, which is about 28% less.

[DavidPIL]

yeah, it is kinda low... rather large drop. My old Ranger would drop from 26-27 down to 18 or so which is in that 30+% range but the next Spring it jumped back up. What I didn't realize is that I nearly doubled my city driving time compared to Highway per tank so once again, another variable which could cause the issue. If he driving is the same as it was previously, I would be concerned as well but with this happening in the Winter, it's really hard to say it's not normal. I just wouldn't be concerned unless it continues to go down or doesn't come back up in the Spring. He did mention station jumping... Maybe something from a bad fill-up is cloging somethin... That's always possible... Hell, it could be something major but I would think he'd notice some drop in performance, wouldn't he? Wonder if someone else in Minnesota can chime in on their mileage. I dunno.... I'm no expert, that's just my experience.Dave

[GlenW]

I put on 7000 miles since I purchased my Base Vibe on 10/13/03 and I keep track of my fuel at every fill up.Heres a rundown:Minimum mileage 12/16/03 - 21.73 mpgMaximum mileage 10/20/03 - 35.03 mpgAverage mileage from 10/13/03 - Present - 28.26 mpgI also noticed that I get a little better milage using mid-grade fuel as well.

[hcsem]

Thanks for the responses so far.Anyone have any idea when they would have switched the fuel mixture around Minnesota? Somehow I think that happens in October, but I'm not certain on that.I jump stations, but generally it's a 66 station or a BP/Amoco.Performance wise, things seem unchanged. 80mph @ 3000 rpm seems about the same as it was in July.90% of my driving is highway driving with the cruise control set, so if anything I thought I'd see #'s closer to 37mpg.Either way, I'm a #'s person so I'll keep watching at every fill up. Just not getting the high gas mileage I expected and wanted.Thanks.

[pmh013]

Good that you're keeping track of the numbers. You'll need those if you want to complain to GM about your mileage not being what you expected. I wonder if you've got fluctuating fuel pressure? That was one of the many diagnoses they made on my car during my catalytic converter episode. They changed out the fuel filter, but of course it didn't resolve the problem completely (it did make it a little better, but I think it was in my head).In any case, definitely stay away from "freshly refueled" stations. Why take the chance that some high school kid didn't put the filter back in and suck in all that crud off the bottom of some tanker?Our "winter gas" doesn't usually come in until mid-October. I wonder if your local gas station could provide this info?

[huy397]

I noticed my milage is down too. I figured it's because of the warm up time and winter gas too.As for gas, I usually gas in in Extra Food or SuperStore ( for their super bucks ) should I switch to 'main stream" gas station ? thanks

[pmh013]

Quote, originally posted by huy397 »As for gas, I usually gas in in Extra Food or SuperStore ( for their super bucks ) should I switch to 'main stream" gas station ? I don't know where SuperStore gets their fuel from. I can't recall ever seeing a tanker at the one in Regina, so it would be a guess. I do know that my fiance found that he got better mileage in his diesel Jetta when he stopped getting fuel at SuperStore. He now fuels up at Co-op.It might be an interesting experiment, to switch to a Shell/Esso/Petro-Can and see if there's a difference. Of couse, I'm weird, and I think these things are interesting.

[hcsem]

Just a quick update.I'm still keeping gas receipts. I was in Wisconsin last week, and did see a slight improvement to around 29 mpg. Now that I'm back in Minnesota it's right back where it was before.I got a "thank you" letter the other day from the dealer that looked at my Vibe and concluded nothing was wrong. I had to laugh at the line where they asked me to contact them if I'm not satisfied. They knew I wasn't satisfied when I picked it up. How could I be satisfied if they concluded nothing is wrong, and I've got gas receipts to say something is? Go figure.In the VW Jetta that my Vibe replaced (don't ever buy VW), I used to use an engine cleaner called "Sea Foam" about once/month, and that was helpful. So I'm going to give it a try in the Vibe and see what happens.Stay tuned.

[pmh013]

Let me see if I understand this.Your mileage in Minnesota sucks, but it's OK in Wisconsin?What is different in the 2 states (other than a passion for rodents)? Gas stations. Altitude (hardly). Weather (maybe). Driving style. Damn it, now I want to go to Madison for custard. Just thinking about Wisconsin makes me hungry.

[red]

well, after our recent round of below -30* weather....my mileage bottomed out at 16.77 mpg....and that doesnt include alot of idling...i have been averaging 18 -20 mpg in the 0* weather but it really drops when temp gets below -20*....if my awd kicks in alot the gas drops also! overall the mileage isnt that great in the winter, that was confirmed by the tech mgnr at the dealership also. Even in the summer i dont get great mileage..approx. 23-25mpg, but i take what i can get!!

[joatmon]

Here's the info from the service manual(p. 6-563) on what to check if lower than expected, or lower than it used to be.Preliminary ChecksCheck the air cleaner element for dirt or restrictionsVisually and physically check the vacuum hoses for splits, kinks, and proper connectionsCheck the owner's driving habits for any of the following:*The A/C system defroster mode is ON all the timeThe tires are improperly inflatedHeavy loads are frequently being carriedHeavy acceleration and high speeds are commonFrequent short tripsProlonged periods of idlingDriving on unpaved or rough roadsSuggest that the owner refill the tank and recheck the fuel economyFuel System ChecksCheck the type, quality and alcohol content of the fuel. Oxygenated fuels have lower energy and may deliver reduced fuel economyCheck for the correct fuel pressureIgnition System ChecksInspect the spark plugs for correct operation and good igntion system performance.Check the ignition coil boots for cracking, chafing and loose connections.Observe the Spark parameter on the scan tool at idle, while operating the rear defogger, the A/C system or the headlights. If the scan tool display remains fixed at 10 degrees, check for a short to ground in the Diagnostic Request circuit from the powertrain control module (PCM) connector C4 terminal 20 to the data link connector (DLC)Check the knock sensor (KS) and the sensor circuit shielding. A faulty knock sensor or signal interference could cause excessive retard of the ignition timing avance. Observe the Spark parameter on a scan tool and compare with a known good vehicle. A typical value at 98 kmm/h(60 mph) with all engine accessories off is 26-32 degrees.Cooling System ChecksCheck for the correct engine coolant levelCheck engine thermostat for always being open or for the wrong heat range.Additional ChecksCheck the clutch adjustment in vehicles equipped with a manual transmission. **Check the transmission shift pattern and the torque converter clutch (TCC) operation in vehicles equipped with an automatic transmission.Check for dragging brakesCheck for uneven or premature tire wear. A suspension misalignment can cause reduced fuel economy ***Verify that the wheels and tires are similar to OEM. Wide performance tires create more drag and taller tires can cause odometer discrepancies.Check for (sic) the speedometer for proper calibration.Check for green engine. Fuel economy may not be near expected levels until the engine has had 5,000 - 8,000 km (3,000 - 5,000 miles) to break in.Check for add-on equipment like luggage racks and carriers. Wind resistance can lower fuel economy.Check the Service Bulletins for any updates or information.______________________________________________________________________________________*If you take it in to the dealer, be ready to swear that you don't do any of the bad driving habits. Also be prepared for them to tell you to "refill the fuel tank and recheck the fuel economy", but you probably wouldn't be at the dealer over a single bad tank of gas.**Interesting, didn't know there was a clutch adjustment. Checked , and it refers to a section on clutch slipping. possible causes for clutch slipping are weak diaphram spring, oil contamination, or excessively worn, exploded or damaged disc. No adjustment though.***Wonder if there is any correlation between people with fast tire wear and people with poor fuel economy.Also interesting that there is no reference to the clogged exhaust problem like pmh013 had, maybe they figured that would show up as a performance problem instead of as a fuel economy problem.

[joatmon]

I need to go throough this list myself for my own car. Over the last 12K miles or so, my gas mileage has been dropping off, more than I would expect for just "winter gas", or at least more than it did last winter.

Attached files

[sylvainber]

i get about 28-30 mpg in summer and 26-28 in winter. (base 5spd). I have found that my mpg drops most if i step on it too much in the winter (more so that in summer).we had a very cold spell last winter and warming up the car did make a big dif in mpg. It hasn't been that cold this winter so i haven't had to warm the car ahead.

[ToolGuy]

Start with the basics, when was the last time your air filter was changed?