Average MPG readout is acting very strange...
#2
03-12-2009, 11:49 AM
Active Enthusiast
Join Date: May 2004
Location: Garland, TX
Posts: 76
Re: Average MPG readout is acting very strange...
You did not say if the ICE is running or at auto-stop. If the engine is running at a stop, which is normal in cold weather, or when you have a heavy electrical load, like running AC, then your average fuel economy should drop at a stop - you are using gas, but not going anywhere.
If the engine has auto stopped, then, yes, I agree you have a problem and the average economy calculation is out of whack.
OT: fun with average fuel economy. I have a gas station right at the entrance to my neighborhood. I often fill up on the way home (with a warm engine), reset the average, and drive home slow enough to keep it in EV mode. If someone comes over, I can show that I'm getting outrageously high mpg in the Tahoe (or my wife's Prius). Of course, when I drive to work the next day, it drops back down to normal ranges.
If the engine has auto stopped, then, yes, I agree you have a problem and the average economy calculation is out of whack.
OT: fun with average fuel economy. I have a gas station right at the entrance to my neighborhood. I often fill up on the way home (with a warm engine), reset the average, and drive home slow enough to keep it in EV mode. If someone comes over, I can show that I'm getting outrageously high mpg in the Tahoe (or my wife's Prius). Of course, when I drive to work the next day, it drops back down to normal ranges.
#4
03-12-2009, 02:17 PM
Active Enthusiast
Join Date: May 2004
Location: Garland, TX
Posts: 76
Re: Average MPG readout is acting very strange...
I've done that in the past, and yes, it will always drop immediately. This is what it should do. Whenever you start, the ICE always runs until the car gets to the proper temperature. This is the "start-up penalty" and why short trips will give you lower MPG than longer trips.
Maybe retry your experiment, if you are warm starting the Tahoe, but put it into drive after starting, then back into park. You might need to roll forward a bit before putting into park, or just hold the brake, just to make sure the ICE cuts off. (Should display auto-stop and V8 Mode if you are an the screen that shows instant MPG) then switch back to avg mpg and see if it stays even.
I'll try to play around with this tonight.
Maybe retry your experiment, if you are warm starting the Tahoe, but put it into drive after starting, then back into park. You might need to roll forward a bit before putting into park, or just hold the brake, just to make sure the ICE cuts off. (Should display auto-stop and V8 Mode if you are an the screen that shows instant MPG) then switch back to avg mpg and see if it stays even.
I'll try to play around with this tonight.
#5
03-13-2009, 07:00 AM
Active Enthusiast
Join Date: May 2004
Location: Garland, TX
Posts: 76
Re: Average MPG readout is acting very strange...
Gruson,
I drove from work to pick up the kid at daycare, reset the avg. MPG about a mile away, and had a 36 avg. when I stopped. When I got back in the car and started it up, the ICE ran, causing the avg. to drop rapidly, as I would expect since it is using gas and not going anywhere. I put it in drive, rolled a few feet and stopped. The ICE went into auto-stop (the Tach gauge dropped down the auto-stop zone) and the avg. mpg stayed steady. I placed the car back in park, and the ICE stayed off, avg. mpg stayed steady. I then backed up to get out of the parking spot, the ICE came back on as soon as I put in in R. Avg. MPG started dropping again.
I believe this is all normal operation and is consistent with my understanding of how the Gm 2-mode hybrid system works.
I drove from work to pick up the kid at daycare, reset the avg. MPG about a mile away, and had a 36 avg. when I stopped. When I got back in the car and started it up, the ICE ran, causing the avg. to drop rapidly, as I would expect since it is using gas and not going anywhere. I put it in drive, rolled a few feet and stopped. The ICE went into auto-stop (the Tach gauge dropped down the auto-stop zone) and the avg. mpg stayed steady. I placed the car back in park, and the ICE stayed off, avg. mpg stayed steady. I then backed up to get out of the parking spot, the ICE came back on as soon as I put in in R. Avg. MPG started dropping again.
I believe this is all normal operation and is consistent with my understanding of how the Gm 2-mode hybrid system works.
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