I have an '07 Mazda 6. I really like it and it gets great gas mileage. At least it used to. Over the past few months, my mpg has went down from about 28 to about 23. That's a combination of city and highway driving. I don't know what the problem is. I got new tires in the first week of December. I get gas from the same several stations that I always go to. It just turned 70,000 miles. It's slightly over needing an oil change, but no worse than it's been before. I also had it aligned when I got new tires. I don't drive any differently than I have in the past. But for some reason I can't get the mileage I used to get. I used to be around 300 miles on a half tank of gas. Now I'm lucky if it's 250. If anybody has any suggestions, I would really appreciate it.

Thanks.

 

I'm guessing from your post that you have a 4-cyl automatic and that you normally drive very conservatively? 28 is excellent mileage for a 4-cyl/auto 1st gen Mazda6 under the conditions you describe.

It could be a number of things, B, but also consider the ethanol they are now putting in almost all the gasoline sold in the US.
By nature alcohol will afford you worse mileage to the tune of 33% comparing apples to apples (100% gasoline vs. 100% ethanol.)

I too have been seeing a 2-3mpg loss since then, again driving the same way and the same mixed routes I always have in this car.

You may have an additional problem though. Losing 5mpg using 10% ethanol is a little more than you should expect.

The MAF sensor could be dirty and sending false readings to the ECU but not bad enough to cause any real problems, or a CEL yet.
Or you might have an O2 sensor that's getting too long in the tooth.
Your spark plugs may be due for a change as well.
You may be getting the occasional misfire due to a weak or faulty coil pack.

Tires can also be a mileage factor, if they're rolling resistance is high compared to what was on the car before. And the fact that this problems seems to have started right around that time, you may already know why?
It could also be a poorly done alignment.

To a lesser extent, it could be a dirty air filter. Is the car burning/using oil? Does it seem to run rich?

In any case, it may be time to look into some of those issues I described. Feel the car out, if it's acting differently than you remember it before.

 

Yeah,28 MPG sounds incredebly high to me as well,i'm getting around 25-26 with 75% highway driving and very light on the trottle with an '05 auto/4 cyl.I can go 250 miles with half tank,no more than that.Keep in mind that in the wintertime every car gets worse mileage due to warming-up issues.

 

Thanks everybody for the feedback. I'll keep these things in mind and have them looked at. I hadn't thought about getting worse mileage in the winter. It was about the time that it got really cold here that it started happening. I don't understand how I got such good mileage while everybody else is getting worse than that. It is a 4 cylinder automatic. But I've gotten 500 miles on a tank and put about 17 gallons in the tank to fill it up. That's 29 miles per gallon. My drive to work everyday is pretty simple. It's 28.2 miles each way. About 22 of those miles are on a country road that I drive about 60-65 mph. There are usually other cars and I guess I draft off of them. Several years ago I drove my car on vacation. It was 99% interstate driving. When I filled it up and calculated it, I had gotten just over 32 mpg. So it doesn't really make sense to me. Oh well. Thanks again for the helpl.

 

There's no way you're getting that kind of mileage. Either you changed tire size, or your odometer is just plain wrong, either way giving you an exaggerated sense of miles driven. Also, if you're routinely letting yourself get so low on gas that you're adding 17 gallons, you're running the risk of damaging your fuel pump, which is cooled by the gas in the tank.

 

That doesn't make sense to me either. I admit that I know next to nothing about cars, but it doesn't seem right. When I got new tires in early December, I told the store the size of my tires. I haven't actually looked, but I assumed they didn't make a mistake and put the right size back on. I've got the same wheels, so wouldn't the tires have to be the same size? Like I said, I don't know. As far as the odometer, nothing has been done to it to make it change. I don't regularly let my gas get that low. It was a rare occurrence. I will have had my car 4 years this coming May, and up until about 2-3 months ago, I showed right at 300 miles for half a tank. I commented to people that my truck I had before it would only get about 275 miles on a tank, but my car gets 300 at half a tank. I guess the odometer could be wrong. But if it's correct now, it fixed itself. Oh well.

 

You don't say where in the country you are, but during the winter months, gas stations are required to use additives to gas that reduce smog. MBTE is one of those gas additives. Ethanol is another. The idea is to increase the vapor pressure of the gas to prevent hard starting of cars. This also prevents a rush of hydrocarbons to the atmosphere.

You mileage will improve in the spring. Come back in two months and tell us where your mileage is.