Why an Aveo automatic gets poor city MPG

[ontarian_frog]

You still don't get the meaning of overdrive. Unfortunately, you still don't understand the way the transmission functions.

[MetroMPG]

I found it actually shifts at about 15, 25, and 45 MPH. In other words, the upshift into the highest gear (fourth) is much too late. Most 4 speed transmissions typically shift at approximately 10, 20 and 30 MPH. The delayed shift into high gear at around 45 is a major reason for delivering poor city FE. I live in suburbia. On major roads, typically the speed limit is 40.

Based on that description of your typical speeds, sounds like the pedal / TPS fix may get you into top gear/torque converter lockup sooner & more often.

Here's hoping you'll be reporting a jump in fuel economy soon.

[Thymeclock]

You still don't get the meaning of overdrive. Unfortunately, you still don't understand the way the transmission functions.

I think I do. Fourth gear, in effect is 'overdrive', whether they call it that or not. There is no higher gear; it's a four speed. An automatic transmission is not fully (or solidly) 'in gear' until the torque converter locks up. That's the way a fluid drive torque converter works. But on an Aveo it doesn't lock up until 45 MPH. On most other cars it will lock up sooner, more like at about 40 or so.

So what about that do I not understand?

[Thymeclock]

Based on that description of your typical speeds, sounds like the pedal / TPS fix may get you into top gear/torque converter lockup sooner & more often.

Unfortunately it doesn't. The torque converter still doesn't lockup until 45. But at least now I can feel a pronounced up-shift into fourth gear sooner, at about 32 MPH rather than 38. So there is some improvement in the way it is shifts, and it's now more in line with the manufacturer's specs.

If we return to the applicable graph of shift points:

download/file.php?id=919&mode=view

we see the lockup mode (4L) illustrated on the map. According to the chart the lowest speed at which it can ever enter lockup is at about 42 MPH (68 KPH on the graph). Also, according to the graph, it will drop out of lockout mode unless a constant speed of about 40 MPH is maintained. Apparently that's the way it was designed, and there's no way to change it.

All our local speed limits are 40 MPH at most, and that's about what traffic on the road averages - so I can't go any faster than the car in front of me. If it were to enter lockup at 40, as my other car does, it would be better. Yes, that few MPH difference matters in my case. I guess I could call it the Chevy disadvantage.

[hammsaveo]

When I test drove one I didn't mind it.I just new I could get one cheaper if it was a manual. Can someone explain the power button on shifter for the auto?

[thehunterooo]

the hold button?

mine keeps me in 3rd gear when im in D

i never really have to go into 4th gear, its very helpful with city driving and such

[hammsaveo]

How is it helpful? I didn't realize you had the auto?

[thehunterooo]

instead of shifting into fourth gear at 20mph, i can stay in 3rd gear, i like it better

yeah, im stuck with an auto, i would have a small turbo in here in a heartbeat if it was a manual though

[Thymeclock]

instead of shifting into fourth gear at 20mph, i can stay in 3rd gear, i like it better

yeah, im stuck with an auto, i would have a small turbo in here in a heartbeat if it was a manual though

Your car does not shift into 4th gear at 20 MPH. The shift points occur (approximately) as follows: second at 15, third at 25, fourth at 35, followed by torque converter lockup at about 45 MPH, which feels like a shift but it's actually the torque converter locking up.

So at 20 MPH you are actually still in second and are locking in second gear. You might have more acceleration, but it won't help your fuel economy.

[thehunterooo]

ah ok, that makes sense, thank you =D>