Figure it out with a Calculator after a fill up, my Trip Computer is normally 2 gallons off, but my Explorer was always about 5 off when it was in-town driving

 

That'sterrible mileage!!
I had read that places in St. Louis, bylitigation,were putting"levels" of ethanol in their fuels and were NOT required to listit@ thepump. Ethanol, as all alcohols, carries it's own, molecule ofO2 and thereforeis not as efficient (~66%) compared to straight gasoline which does not carryO2 with it. It takes more alcohol by volume (~33%) to produce the same power as gasoline and maintain the proper mix of 14.7:1.
I wonderif the same is truein Ca? Could that be why all of your cars are "suddenly" getting worse mileage?

 

Two possibilities are, 1) You've got a gas leak somewhere, or 2) Either your parking brake, or your regular brakes, are not releasing completely.

You can do a bit of a sniff test re: a possible gas leak. Pop the hood before you start the car - do you smell gas? You can kneel down and sniff underneath the car. If you smell gas, you may have a leak somewhere.

The dealer should be able to check your brakes out very easily. Make sure they check both the parking and the regular brakes.

A third possibility is your car for some reason is pushing too much gas into the cylinders, it is not burning, it is just being exhausted out the back. The dealer should be able to check this for you, too. If you always have a lot of white smoke coming out your exhaust, this can be a sign there is unburnt gas being vented into the atmosphere.

 

California is now putting ethanol in **** gas. Sun On of a ****. It makes the gas burn cleaner but what are we losing for it? I brought my car to the dealer today, they checked it out and found out that nothing was wrong with it. I told my service advisor can you give me a little more information. They told me they could not find any codes. I told them there where never any codes. They are insisting that it is the way I drive. I filled up my tank tonight. I calculated my mpg 19.7!!! WTF! What can cause this!! I checked for leaks, couldn't find any. I had the dealer check my brakes they said they were fine. Replaced the air filter last week. I am going to replace the fuel filter tomarrow.

 

The law in NY (not sure other states) says the maximum of ethanol addition to gas is 10%, but no one really checks I guess.
I am getting consistently 26.8 on mostly local drives in this winter, 2.0L touring.
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I am having the exact same problem with my 3i Touring. Ihave CONSISTENTLY gotten 29-30 mpg for the last 30,000 miles on my Mazda 3. I drive 80% highway and in hte last 2-3 months have been getting 22-23 mpg. My jaw dropped when i read one of the earlier posts with the same exact experience.

I took the car to the dealer. They said there were no trouble codes so they had no idea. Said the fuel/air mixture was right on. They gave me a program update to correct a shifting bug (common) and that's it. The problem remains. Per their advice, i did a fuel system clean and changed the air filter... no impact. They told me about changing gas mixtures for the winter season, but this is the THIRD winter I've had this car and nothing like this has happened before.

Does anyone else notice that there's a "sputtering" sound during low speed 4th gear acceleration? This symptom appeared at the same time the gas mileage dropped. Also, I notice an intermittent rough idle. It's subtle, mind you, but the car will shake intermittently at idle.

I live in St. Louis, so the ethanol mix might affect me... but why haven't I had the same issue on my other vehicle or heard this from friends, family, or co-workers?

 

I have a 2005 Mazda3 s 5MT. I'm in a process of researching the gas mileage issue as I like to trade it in for a 08 Mazda3 GT model. I understand that the engine mechanics did not have any major modifications since 2004. However, there is a PZEV factor in play since 2007.
I have kept complete detailed gas mileage data for the past three years (40k miles) and come up an average of 31.9 mpg with 70% freeway driving (60-70MPH). The gas mileage has been fairly consistent other than varying with the weather, average as low as 28 in winter and 34 in summer, increasing slightly but steadily during the first year. I seldom use A/C as the weather here is fairly mild. I have gone through and watched gas mileage for a few cars I have owned. Here are a few things I found that you may want to pay attention if you care about your gas mileage. They are all applicable to my Mazda3. - USING A FEATHER FOOT ON YOUR GAS PADEL WILL NOT NECESSARILY GET YOU GOOD MPG. Accelerating at a normal pace, up shifting between 2500 and 3000 RMP on this 2.3L w/ stick shift, and maintaining a steady speed between 35-50MPH in fifth gear will get you an amazing gas mileage. - Using gas with ethanol will definitely reduce your gas mileage, but by no more than 10% as the maximum amount of ethanol shall not exceed 10% or your check engine light might come on due to the large discrepancy between O2 sensor and fuel injection reading. Expanding the topic a little: adding 2-3oz of pure acetone to the gas MAY reduce the effect of ethanol. Personally, I see a marginal, 5-10% increase in mpg on this engine with acetone. So I neither endorse nor discourage using acetone with your Mazda3. - Talking about mpg, it’s all about engine efficiency. You find sweet spots on your engine and stay there. Generally, early up shift without burdening your engine is the best way to save gas. Something about this 2.3L engine, no matter what I do, it won’t average more than 34mpg even for a long trip on the freeway. Of course, I refuse to drive like grandpa or go under speed limit. I like to pass and that’s how you get your money worth…zoom-zoom. - What you do during your break-in period is important! Do not baby the engine or trash it either during the 1st 1000 miles or so. Give your engine a good work-out, accelerating and cruising at different RPMs. Try to use engine break at different RPMs as well. This will give you the best break-in of the engine and therefore better efficiency down the road. Shift often even if you are running at a constant speed. Downshift to slow down. But you only have to do this during the break-in period. - Human error is the largest contributor to the myth of fluctuation in your gas mileage. A mpg drop on a single tank may be caused by various reasons. Maybe you did not fill the tank all the way up last time and making it up on this calculation. Have you been through an oil change? Your car could be left idling while the technician was having a lunch. Have you been to busy drive-through lately? Extended circling in a parking log searching for spots is guaranteed to (seriously) lower your mpg, unless you’ve outfitted your Mazda with hybrid technology. - Coasting at low RPM (<1500) uses more fuel than in higher RPMs. If you have to use brake to slow down after a coast, raise the engine RPM by choosing appropriate gears. At a higher engine RPM, usually above ~1400, and closed throttle, the fuel is cut off. You are using the energy of the car to run the engine. - Do not blindly trust your on-board computer. It may or may not be accurate and is for you to compare among different situations only. Reset your trip meter every time you fill up and record mileage with next fill up. An average over a few tanks with consistent driving styles is a true reference to your fuel economy. The biggest unknown for me is the effect of PZEV equipment on 2.3L engine. It seems that the PZEV standard only cares about harmful emission gas but not CO2 which is directly related to the amount of fuel burnt. So the gas mileage could be harmed in the process of achieving “cleaner” exhaust gas. If this is the case, I’m keeping my old Mazda3. Please let me know if anyone has such information. Thanks in advance.

 

These all seem like good tips for driving, but they don't explain how a few of us have had steady gas mileage (30mpg)for 30,000 miles and then suddenly drop to 22-23 mpg with no change in driving pattern.

I check fuel economy every fill up without fail. I have steadily achieved anywhere from 28-32 mpg for the last 2 years (30,000 miles) of driving my 2006 Mazda3i Touring AT. Nominal is 29-30mpg.

All of the sudden, I started getting 22-23 mpg. A 25% drop in fuel economy almost overnight has to have a reason and it isn't driving style for us that haven't changed either our drivingstyle or routine. And to get a 25% drop in fuel economy suggests a MAJOR change in driving, as in Dukes of Hazard driving style.

 

I wouldn't drive 35 mph in fifth gear. This engine's sweet spot is definitely NOT driving 35 MPH in the top gear. I have found having your revs in the 2750 to 3250 range is where the best MPG is achieved.

If what you say is true, Mr. Rant, that you can get 10% better MPG with acetone, why would you not endorse its usage? I would not put acetone in my gas. Acetone is corrosive.

http://www.snopes.com/autos/techno/acetone.asp

 

How long have you been getting this low mpg number? Have you been using the same gas stations? If this happened right after a car service, think what could've gone REALLY wrong. Usually, even a wrong grade of oil wouldn't have such a major affect. Did you notice any difference in operation when it happened? Most likely you would feel some (or major) difference in engine power when you have a 25% drop in fuel economy. If this was not a temperary issue, I would suspect something wrong with the car or (contaminated) gas.