MPG readout having dropped while vehicle is off?

[jackka]

Does anybody else notice the MPG readout number having dropped while the car is off?

for example, I would have 22.2 MPG when I get home or somewhere and turn off the car, and then the next time I start it, it would be 20.1.

I don't think that it was always like this.

about a month into owning the car, the sunroof stopped working and i took it to the dealership where I don't know what they did, but I had to reset the clock on the dashboard.


It seems like now I can never get 26-27MPG that I used to get for commute for the first few weeks. Though I'm not sure if it has anything to do with taking it to the dealership or some other reason just happened to be around the same time.

I'm pretty bummed out that my MPG has decreased significantly instead of getting better after break-in. It has 3500 miles on it now and MPG is around 21-22 most of the time.

While getting 22MPG in itself doesn't bother me too much, it's not knowing whether I have some kind of a problem or not that really bothers me.


PS: I can already see some replies that go like "YOU BOUGHT THE WRONG CAR, DUDE." or "DRIVE A PRIUS IF YOU CARE ABOUT MPG" that always follow any post that deals with MPG, lol. Yeah yeah I get it, the Camaro is a sports car. Well, some people like driving awesome looking cars without revving the engine at every single stop light followed by a tire-screeching takeoff, so please do everybody a favor and save yourself the time and energy of saying such things. It helps no one and does nothing other than to broadcast your ignorance...

[SSLarry]

Not sure why that would happen, but I would say that the MPG calculator is spot on. I tested it on three occasions (three different fill ups), and it was within 1 mpg of what I calculated after 200-240 miles.

[John Shields]

Mine moved a lot when I first got it, but it's only been moving slowly since. Nothing like you described.

[Bogie]

If this is like other GM cars, the mpg has an averaging interval. I wouldn't be too concerned about the reading without having a better understanding of the interval as it relates to driving conditions. For example, if you reset the interval, and go on a long freeway cruise, the actual and displayed mpg will be high. Subsequent city driving will result in an actual reduced mpg, but the displayed mpg will be higher because it is still averaging in the high mpg from the cruise.

If the interval is long (in some GM cars it only resets when you reset it), the average over a year or more of driving will pretty much swamp any short term changes....resulting in a reading which doesn't budge much at all.

If you're still concerned. Figure out how to reset the avg. Then track fuel manually....by writing down odometer readings and gallons at each fill up over several cycles. See if the manual method matches the display.

[cab2g]

I have noticed this on my 2011 SS... It drops 0.2-0.4MPG sometimes when I start it. But I figure that's because the engine isn't broken in.

[clg_98ta]

Originally Posted by cab2g

It drops 0.2-0.4MPG sometimes when I start it. But I figure that's because the engine isn't broken in.

Not sure I follow that logic...

[Waco]

Maybe it's going out at night without you?

[BalogUK]

ill take a 2-3mpg hit just by cranking the car in the AM, about a mile down the road it recovers to its "evening" # from when it went into the garage... dunno if it takes more fuel in instantaneously right at cranking before the pcm afm's average out but whatev... like i said, it usually recovers pretty quick.

[skuttduck]

My observations. The moment you start the car, it uses more gas in order to warm up.

If I reset the MPG, and then start the car I will see this drop.

Now I haven't reset the MPG setting since driving to and from Oshawa, and I'm at a constant 24mpg.

When I drove too and from Florida last year I got 27.5 mpg.

Straight conservative 25 - 35mph city driving, I get 20 - 21 mpg. Most of that is letting it coast though.

I actually got the 21mpg city with 2 tanks of gas with premium though.