My 2011 m37x is avg. 12.9 gas mileage why?

[perkdaddy]

Hey you guys! Just bought a 2011 M37x. Love the car! When I purchased it I researched the gas mileage and found anywhere from 18 to 20 in the city and 22 to 25 on the hwy. Now, when I'm driving and looking at the average miles per gallon on the info screen, I'm registering 12.9! With these high gas prices I'm very concerned! Is there something I'm doing wrong or is there something I can do to improve the gas mileage. What kind of gas mileage are some of you guys getting? Thanks in advance for your suggestions!

[alms24sebring]

Are you really as perky as they say

[Razi]

When was the last time the various filters were replaced?

[Bubba1]

When was the last time the various filters were replaced?

This ^ but there are so many other things to examine including (but not limited to):
1. tire inflation: under inflation lowers gas mileage
2. Your driving style: For example, are you aggressive and drive fast?, Do you coast up to traffic lights or brake at the last minute? Do you tailgate or leave a lotta distance and keep a more steady speed? Do you like to wind er up when you accelerate?)
3. The type of driving you do. (ie. if you're doing mostly hwy driving on cruise control vsr lotsa city stop/go.
4. Are your trips in the car mostly short hops or longer rides
5. do you let the car warm up in the morning?
6. do you have a lot of extra junk in the trunk? (the car that is)
7. Do you run the climate control system most of the time?

It's certainly possible it's one "aha" mechanical thing, but in many cases, it's the accumulation of many little things. For example, if everything checks out fine except you drive 75 vs 60 on the highway, you're probably using 10-15% more gas. That' significant just by itself. Good luck.

[Mr1der]

are you going half the distance on a tank of gas or is the readout just retarded?

[s0m3th1ngAZ]

Yeah, have you actually calculated it by hand?

[MinisterofDOOM]

How does the MPG readout in the M work? Does it let you reset it on-demand? Do you reset it every time you fill up? If you are resetting the reading regularly, are you resetting from a stop, or while moving? All of these things could impact your numbers. Also remember that you need a decent sample size (miles travelled) before the reading will be acurate, since it is an average. I've manipulated my LS's readout to show 65mpg before by resetting it before coasting throttle-free down a long hill in 5th. I've also seen as few as 8mpg when I've reset the MPG reading and then proceeded to immediately vaporize some tires (using lots of gas and not moving is obviously not good for MPG). I'd say give it at least 50 miles before you put any stock into what that display says. I generally don't reset mine very often, and it always homes in on the same average over time: 17.4. It fluctuates a lot if I reset it frequently, but long-term (400+ miles) it always goes back to the mid-17s. Of course an LS8 is not an M37x, but this should all apply to any car with a fuel economy readout.

I also recommend manually calculating MPG to confirm the accuracy of your MPG reading in-car. Calculating based on fuel added on a topoff isn't 100% accurate, either, but at least it'll give you a basis for comparison. If your math says 20 and the readout says 13, there's definitely something goofy going on.

When was the last time the various filters were replaced?

This ^ but there are so many other things to examine including (but not limited to):
1. tire inflation: under inflation lowers gas mileage
2. Your driving style: For example, are you aggressive and drive fast?, Do you coast up to traffic lights or brake at the last minute? Do you tailgate or leave a lotta distance and keep a more steady speed? Do you like to wind er up when you accelerate?)
3. The type of driving you do. (ie. if you're doing mostly hwy driving on cruise control vsr lotsa city stop/go.
4. Are your trips in the car mostly short hops or longer rides
5. do you let the car warm up in the morning?
6. do you have a lot of extra junk in the trunk? (the car that is)
7. Do you run the climate control system most of the time?

It's certainly possible it's one "aha" mechanical thing, but in many cases, it's the accumulation of many little things. For example, if everything checks out fine except you drive 75 vs 60 on the highway, you're probably using 10-15% more gas. That' significant just by itself. Good luck.

I don't even think all of those things COMBINED in exceptionally out-of-spec condition could cause an M37 to get 13mpg. That's astoundingly low. I've managed that by hot-rodding 6-liter half-ton pickups, but even my Q45 and LS8 being driven like mad bats from Hell never hit 12. Not that I'm questioning the wisdom of keeping on top of those things, but when you're talking about a near 50% change in fuel economy I'd say there's something else to blame.

[nissangirl74]

I don't trust the average mileage indicators. After the 700 mile tank in the Insight, the mpg average read 63.4. When you did the Math, it was actually 71.4. That's a helluva difference.

[Bubba1]

I don't even think all of those things COMBINED in exceptionally out-of-spec condition could cause an M37 to get 13mpg. That's astoundingly low. I've managed that by hot-rodding 6-liter half-ton pickups, but even my Q45 and LS8 being driven like mad bats from Hell never hit 12. Not that I'm questioning the wisdom of keeping on top of those things, but when you're talking about a near 50% change in fuel economy I'd say there's something else to blame.

I humbly disagree, we're talking about 9mpg from the median, perhaps less depending on OP's type of driving, which we don't know. All of those things combined can easily reduce mpg by that amount. Heck, driving faster on the highway could account for 1/4 to 1/3 of it by itself. My Z reliably gets in the low-mid 20's, but it doesn't take much effort on my part to cut it in half.
I'm certainly not accusing OP of driving crazily, my point is simply there are many factors that negatively influence mpg, it might not be just one thing.

[frapjap]

Not sure if your dash is throwing a code or anything, but when my gas mileage varies that much and it isn't due to a heavy right foot, its usually that an 02 sensor (or two!) have gone bad.