Anyone experience a decrease in MPG. My mpg has always been 15.9 consistently. Just overnight it dropped to 13.8. Any ideas?

 

quit using the valet.... or, as the almighty commander once said... "check your tire pressure??". (joke).


What vehicle?
any symptoms?
miles?
length of ownership?
past/present maintenance performed?
what gas station? your go to, or an unknown station/brand than usual?


the post is too vague.

 

how do you measure MPG? May has to do with measurement rather than real MPG loss.

 

that s not enough difference to be concerned. Could be a dozen variables.
Temp, different fuel blend, lower tire pressure, a longer idle period, different driving style for a few mins, etc.

 

The mpg changed after disconnecting the battery. I'm driving a 2006 911S with 25,000 miles. Mpg change is from the readout on dash. Thanks for the advise, I will check the obvious, tires, gas etc.

 

The battery disconnect probably explains it. This causes the car to "forget" all of the adjustments it has made to get your particular engine to run optimally. This is often purposely done after someone makes an engine mod to force the engine to learn new adaptation parameters. Within a couple of hundred miles of varied driving it should re-adapt and will probably return to what you are used to.

 

Another note... this reminds of another post a month or two ago where someone noted that their exhaust sounded more aggressive for a little while after a battery disconnect and then eventually the engine became more subdued sounding. This was likely due to the engine running more richly (aka burning more fuel) right after the reset, giving a more raspy sound and as noted in your case decreasing the gas mileage. You've noticed how raspy the exhaust sounds right after a cold start where the engine is running rich, right? Eventually the engine learned to run the engine more a leaner mixture and quietened things down while also improving MPG and emissions.

 

Thanks, you are right on every account. The car does sound different and when I hear different sounds, I get nervous.

 

Hmmm, I normally would blame our dreaded California winter gas, but that would have happened more like December. So I concur with the battery disconnect folks.

My Audi Q5 2.0T always drops about 2-3 mpg during the winter, and once we get the summer blend back it goes up by the same amount

 

I vary between 25+ to as low as 12.5 depending on traffic and road conditions. I wouldn't be concerned.

 

When the mpg indicator is reset the mileage fluctuates wildly based on short term conditions. It will stabilize where it was before given your average driving style over time. This is probably what the others have said. If so I agree

 

Looks like I just need to drive more. Time for a road trip!

 

I get ~28mpg, but I drive like an old lady going to church.

 

~28mpg here too. I drive like grandpa driving his old lady to church.

 

Near 30 mpg on freeway commute (30 miles one way ... starts at 20 mpg when cold, but gets a lot better when warm). 12 to 15 when I'm playing on the twisties.