jgcarter56

I have a 2005 Malibu 4-dr V6 (the smaller one) sedan. I have about 60,000 miles on it. About a year ago, I started noticing that I was getting about 3 miles fewer per gallon than previous (25 city, 33 highway). It was because of a bad tire and when I kept the tire filled, the mileage was fine. However, after a period of time, this no longer worked so I got a new set of tires in January. It didn't change my mileage and, within the last month or so, the mileage has gotten worse (5 miles fewer per gallon). I've changed the oil, oil filter and the air filter.

I'm in Texas and the dealer suggested that there was a change last September that put more ethanol into the gas (15% instead of 10%) but I haven't seen any notice of that at the places I fuel up. It doesn't seem to matter where I get my gas, the mileage remains the same although I'm thinking about trying to find some 100% gas and see if that makes a difference.

I'm considering getting a tune-up but the car runs fine except for the decrease in gas mileage. I've also read that it might have something to do with an O2 sensor or a temp sensor somewhere but I think I might have already gotten that checked.

Anyone have any ideas?

Tyrod

You don't get much with a tuneup these days. New spark plugs, PCV valve if your car has one. Of course, you'll get the 30 point (or whatever) once over inspection where they do their damdest to find something else wrong. For what little you get with a tuneup, you'd be wiser to do it yourself. Of course there is another tack, don't ask for a tuneup, just ask for a spark plug & pcv valve change. And yes, apparently your car has a PCV valve. At least they sell one for it.

If your spark plugs are the originals then you'd have to figure they're about half worn out. So, even though they're not at their 100,000 mile limit, they've seen a few miles. If you actually had a failed spark plug or failed plug wire or COP or coil then you would at least get an occasional MIL (SES) light. So, I doubt any of that is the culprit.

You could have a failing or out of spec front O2 sensor. You have 2 O2 sensors. One in front of the cat and one behind the cat. The one in front of the cat is the one that sends A/F ratio info to the computer. At 60,000 miles your O2 sensors are still under warranty and if one's failing you can get your local Chevrolet or GM dealer to replace it. I've not heard of an O2 sensor going bad on a Malibu with your low mileage. It could also be a flakey fuel injector. They usually don't go bad with your low mileage. I believe that's another warranty issue.

I think your idea of finding a gas station that sells pure gasoline is a good one. If nothing more than to put your mind at rest. You ought to be able to find one here: Ethanol-free gas stations in the U.S. and Canada

I assume you've had your transmission serviced recently. If not, waste no time in doing so. If you wait until your transmission shows signs of problems, it's too late. Servicing it at that point will only make it worse.

Lastly, I have a stinking suspicion that your fuel mileage woes don't have anything to do with your engine or transmission. I bet you have a bad front wheel bearing (hub). Or possibly 2 bad front wheel bearings (hubs). Malibus are notoriously hard on wheel bearings. Bad wheel bearings cause additional drag on the car. This is not a project for the timid or mechanically uninclined. While it's not a complicated project there are fastener torque values that are difficult to achieve with most shadetree mechanic toolsets. My only advice on this issue is that you buy quality hubs (if one is bad the other isn't far behind). Either get OEM hubs or a quality aftermarket hub like Moog or Timkin. I prefer Timkin. The problem with other aftermarket hubs is that the bearing doesn't go bad, but the integrated ABS sensor goes bad. Just as a point of reference, I bought a set of Timkin front hubs online for my kids 98 Malibu for $71.00 each. Parts stores will get ya for well over $100 for each. Installers will usually add a premium to that as well as the cost of labor. I would think a professional mechanic could easily do the job in 1 hour or less each side. Don't forget you have wheel bearings in the rear as well, but these aren't usually as problematic.

There are other thing that could be bad or going bad, but usually you gt a MIL (SES) light. Not always though! If you get a MIL light, waste no time in getting the code read and report back for further info.

Hope this helps!

P.S. On the gasoline thing, there's no need to buy higher octane fuel no matter where you buy it. Oh yeah I forgot, if your temp gauge on your dashboard is in it's normal operating position then your temp sender is fine. One sender feeds the dash gauge and computer.

tech2

Watch out for e85. make sure you have an e85 or flex fuel vehicle. ethanol blends this high will damage orings, injectors, steel lines not made for e85 fuel. Secondly, an e85 car has a alcohol sensor that allows the ecm to compensate for the different fuel.


Unfortunately you need a scan tool at this point. if no mil are set and fuel trim is within 10%; I would be looking at mode 6 data. A lazy o2 could be present (but not out of paramaters to set a code); and that could be detected here.

Chevrolet Customer Service

Here are some things that can affect fuel economy. I understand that not everything will apply but here is what I have.

Quick acceleration and heavy braking can reduce fuel economy by up to 33 percent on the highway and 5 percent around town. New EPA tests account for faster acceleration rates, but vigorous driving can still lower MPG.



Frequent accelerator pedal movement will reduce fuel economy because of fuel enrichment during the periods of acceleration. Under such driving conditions the torque converter clutch (tcc) also disengages, contributing to fuel economy losses.



Excessive idling decreases MPG. The EPA city test includes idling, but more idling will lower MPG.



Driving at higher speeds increases aerodynamic drag (wind resistance), reducing fuel economy. The new EPA tests account for aerodynamic drag up to highway speeds of 80 mph, but some drivers exceed this speed.



Cold weather and frequent short trips can reduce fuel economy, since your engine doesn't operate efficiently until it is warmed up. In colder weather, it takes longer for your engine to warm, and on short trips, your vehicle operates a smaller percentage of time at the desired temperature. Note: Letting your car idle to warm-up doesn't help your fuel economy, it actually uses more fuel and creates more pollution.



Cargo or cargo racks on top of your vehicle (e.g., cargo boxes, canoes, etc.) increase aerodynamic drag and lower fuel economy. Thus, hang-on luggage carriers, cat toppers, open windows and/or open trunk, etc results in less fuel economy. MPG tests do not account for this type of cargo.



Towing a trailer or carrying excessive weight decreases fuel economy. Vehicles are assumed to carry only three hundred pounds of passengers and cargo during testing. Each 125 lbs. of additional weight results in a .3 mpg loss of fuel economy. Thus, additional passengers, luggage, etc will decrease fuel economy.



Running electrical accessories (e.g., air conditioner) decreases fuel economy. Operating the air conditioner on "Max" can reduce MPG by roughly 5-25% compared to not using it. Electrical loads, (headlights, heated back glass...) also result in lower fuel economy, (typically less than 1 mpg difference, each 10 amps takes approximately .4 mpg).



Driving on hilly or mountainous terrain or on unpaved roads can reduce fuel economy. The EPA test assumes vehicles operate on flat ground.



Road surface condition impacts fuel economy. Gravel and/or pot holed roads decrease fuel economy. Hills (vs. level terrain) also negatively impact fuel economy. Even gradual imperceptible increases in elevation result in real measurable decreases in fuel economy. Similarly, driving in the rain or snow decreases fuel economy.

A poorly tuned engine burns more fuel.

Brake drag (even a minimal amount undetectable by coasting) can have a significant negative impact on fuel economy.



Vehicle suspension misalignment can cause poor fuel economy, new tires, tire rotation, and/or front end alignment may be required to correct fuel economy.

Thanks,

Elizabeth, Chevrolet Customer Service

bluemeanie04

lots of good stuff, I am kind of thinking the wheel hubs also, I've experienced it. Also, I'm just thinking maybe you got shorter diameter tires