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Old 03-04-2009, 10:27 PM   #21
Germane German
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2008 Astra XR
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Default Re: 2500 - the magic number

Quote:
Originally Posted by K-1 View Post
The transmission doesn't lock up the torque converter during acceleration. FWIW, acceleration in any gear is a pig on gas.

For optimal fuel economy (w/ an auto), you want to be in 4th gear, with the torque converter locked up, and going as slowly as possible at a constant speed.
Yes I get that, if I had been more explicit I also would have noted the case where I can get (an alleged) 999.9 mpg at 2,500 rpm by cruising at 2,600 and lifting my foot off the gas pedal. Running at 2,500 rpm in D4 with as little throttle as possible will provide a reasonable rate of speed and a decent level of fuel consumption. I just wish there was a way to find out what my speed and mpg could be in D5 at 2,500. ;>)

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Old 03-05-2009, 01:06 AM   #22
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Default Re: 2500 - the magic number

I guess the only way to find out about a D5 or above for the automatic would be to do a swap with another transmission; question is, who wants to take the plunge?

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Old 03-05-2009, 12:04 PM   #23
Germane German
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Default Re: 2500 - the magic number

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Originally Posted by Teh_Freak View Post
I guess the only way to find out about a D5 or above for the automatic would be to do a swap with another transmission; question is, who wants to take the plunge?
I would in a very strict set of circumstances; if they would approve it under warranty (first 100K miles for drive train) after the existing transmission failed I would pay the shipping and price difference for a 5 speed automatic if one exists that would be a bolt on for the 1.8 liter engine? It would also probably require re-programming, dash gear indicator modification/repalcement and a new shifter and linkage just to scratch the surface so it is clear pretty fast that accepting what I have may be a better adaptation.

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Old 03-05-2009, 04:19 PM   #24
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Default Re: 2500 - the magic number

"Yes I get that, if I had been more explicit I also would have noted the case where I can get (an alleged) 999.9 mpg at 2,500 rpm by cruising at 2,600 and lifting my foot off the gas pedal"

The reason you get a 999.9 inst. fuel economy under the conditions you mentioned is because you have entered Decel fuel cut off. Most all injected engines will cut fuel at some point! The inst. fuel economy is a function of injector pulse width. When the pulse width goes to ZERO, as in fuel cut off, the default on the fuel resolution is 999.9!!

As to fuel economy and RPM. As someone pointed out wind resistance and gear both play a part. The other part is the engine tuning. The BSFC ( brake specific fuel consumption) varies with RPM asa function of engine design.
But as a rule, due to wind resistance and engine speed, the slower you go with least amount of throttle, the better fuel economy.

Several things that take away from fuel economy;

Cold weather- A/F ratios remain richer LONGER during warmup in cold weather, Also engine friction is higher during warmup before the engine reaches full operating temperature and oil reaches operating viscosity.

Heavy throttle during acceleration- There is a point in load ( throttle ) and RPM where the engine enters "Power enrichment". While at low load and speeds the engine runs "Stoich" /closed loop( AROUND 14.7 A/F) at higher loads and RPM the engine A/F ratios are commanded Richer than stoich
( Open loop, to as rich as 12 /1 A/Fand sometimes even richer based on other modes). This happens in Power enrichment when you use Heavy throttle.

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Old 03-28-2009, 08:59 AM   #25
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Dizzy Re: 2500 - the magic number

Quote:
Originally Posted by BNM449 View Post
"I'm curious what kind of mileage you're getting with that driving style."

Robor7:

When the car was new last August I started at well over 10 L/100km, as the car broke in I got down to 8.8 L/100Km.

Now with winter ( slippage) and the winter tires, it's back up to dead-on 9L/100Km.

I expect when spring/summer kicks in and I put the original tires back on, I'll get back down to the mid-to-high 8's.

There is another factor too: when my car is loaded down with my band equipment or pellets for my stove, I drive more conservatively but the load's weight affects my average fuel consumption.

~N~
I just picked up my Astra XE automatic yesterday and so far it is showing a horrible fuel consumption of 13.8L/100K . Did I buy a lemon or should I be more patient (I was not driving aggressively)? I am still under the "30 day satisfaction" guarantee and am having second thoughts.

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Old 03-28-2009, 10:31 AM   #26
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Default Re: 2500 - the magic number

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Originally Posted by THEANALYST View Post
I just picked up my Astra XE automatic yesterday and so far it is showing a horrible fuel consumption of 13.8L/100K . Did I buy a lemon or should I be more patient (I was not driving aggressively)? I am still under the "30 day satisfaction" guarantee and am having second thoughts.
Give it time to average out. Thats been one day of driving, and your conditions probably werent that favorable. I dont know what your driving conditions are in your area (ie lots of hills, stop and go etc) and given the colder temperatures it will be a little higher anyways until summer rolls around again and you see a drop, but you should be seeing no more than 9-10L/100K range. But again, it depends on how you drive and where you live. Good case scenario in the auto is in the 8's but given this time of year you might be typically in the 9's

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Old 03-28-2009, 12:24 PM   #27
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Default Re: 2500 - the magic number

Quote:
Originally Posted by THEANALYST View Post
I just picked up my Astra XE automatic yesterday and so far it is showing a horrible fuel consumption of 13.8L/100K . Did I buy a lemon or should I be more patient (I was not driving aggressively)? I am still under the "30 day satisfaction" guarantee and am having second thoughts.
it should get better,the car needs a break in period.what i'd like to know is where's the 46mpg they boast?got mine at turpin how bout u?

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Old 03-28-2009, 02:57 PM   #28
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Default Re: 2500 - the magic number

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it should get better,the car needs a break in period.what i'd like to know is where's the 46mpg they boast?got mine at turpin how bout u?
46mpg? is that in Imperial Gallons? the Astra is only rated (US of coarse) at 24/30 Automatic and 24/32 Manual.

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Old 03-28-2009, 09:10 PM   #29
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Default Re: 2500 - the magic number

60 MPH is pretty slow, isn't worth it to get 30 MPG

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Old 04-02-2009, 07:51 AM   #30
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Default Re: 2500 - the magic number

Quote:
Originally Posted by THEANALYST View Post
I just picked up my Astra XE automatic yesterday and so far it is showing a horrible fuel consumption of 13.8L/100K . Did I buy a lemon or should I be more patient (I was not driving aggressively)? I am still under the "30 day satisfaction" guarantee and am having second thoughts.
I just picked up mine on Tuesday, and the avg economy on the BC read about 19 mpg. I reset it on the way home, and after ~100 miles of driving, it's now reading over 33 mpg. Make sure you reset it since it's probably done a lot of short hops at the dealer. Remember, a proper MPG reading is done by hand when you refuel. Be patient and it will improve, especially after the first tank or two.

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Old 04-02-2009, 01:39 PM   #31
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Default Re: 2500 - the magic number

When i was driving home one day i decided to do my little old lady, going 50km in 5th gear i was getting 3.2L/100km

88MPG
going 33mph

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Old 04-02-2009, 02:42 PM   #32
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Default Re: 2500 - the magic number

Quote:
Originally Posted by nicolas_p View Post
When i was driving home one day i decided to do my little old lady, going 50km in 5th gear i was getting 3.2L/100km

88MPG
going 33mph
Hehe... Yeah, there's a 2-3 mile stretch on my commute home that's single lane and 30mph speed limit with no lights. Traffic usually flows around 32-35 and if I stay in 5th gear the 'real time' mpg is sick!

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Old 04-02-2009, 03:33 PM   #33
Germane German
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Default Re: 2500 - the magic number

I didn't think about it right away but I did come to realize that my 2008 may have had fuel that was +/- one year old in its tank when I bought it. Obviously that stuff is not going to perform as well as 'fresh' gasoline. For all I know it was also ethanol (cheapest due to subsidies) and that diminishes mileage further. Ethanol actually has two more octane points than regular unleaded around here but each gallon has less energy so less miles per gallon. I can't really try the suggestions for running premium because all of it has been ethanol in it

My favorite instantaneous BC mileage readout is 999.9! It of course means the fuel is shut off to the injectors while coasting but I still try to keep improving my driving habits to wring out that extra tenth of an mpg of economy that would really confuse the BC. ;>)

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Old 04-02-2009, 08:48 PM   #34
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Default Re: 2500 - the magic number

Nice to hear I'm not the only one trying to see of much gas I can save, I normally get around 650km per tank, using the trip meter

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Old 04-05-2009, 12:06 PM   #35
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Default Re: 2500 - the magic number

wow ,is that srictly hwy kms? i cant get more than 500kms on a tank

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Old 04-05-2009, 02:05 PM   #36
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Default Re: 2500 - the magic number

I normally drive at speed of 80km/h or more for half the trip and the other half I stay around 110 km/h

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Old 04-06-2009, 02:11 PM   #37
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Default Re: 2500 - the magic number

I am glad to see my post lives on! I am still happy to say that I am getting a steady 28 to 30 mpg average every day. With the air conditioning on, it drops to around 27. -eh-
I have been able to get a steady 31 or higher driving on our flat highways with cruise on. Its a heavy car and needs more hp, but once its over 30mph, it zooms right along! I am very happy with how it handles twisty roads, the handling and braking are exceptional for this capable little car.
Looking at some of the alternative brand options for the same under $15K I paid I might have gotten more hp, but definitely not the handling. While I love hp, I get more of a thrill in the handling.

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Old 04-06-2009, 09:56 PM   #38
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Default Re: 2500 - the magic number

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I am glad to see my post lives on! I am still happy to say that I am getting a steady 28 to 30 mpg average every day. With the air conditioning on, it drops to around 27. -eh-
I have been able to get a steady 31 or higher driving on our flat highways with cruise on. Its a heavy car and needs more hp, but once its over 30mph, it zooms right along! I am very happy with how it handles twisty roads, the handling and braking are exceptional for this capable little car.
Looking at some of the alternative brand options for the same under $15K I paid I might have gotten more hp, but definitely not the handling. While I love hp, I get more of a thrill in the handling.
The handling/ride sold me on the car as well. It's also nice having leather in a car that's < $20K.

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Old 10-24-2009, 08:11 PM   #39
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Default Re: 2500 - the magic number

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Originally Posted by marx404 View Post
I am still playing around on my 45 min drive to work every day, seeing how I can optimize mpg while not driving like an old granny. I have an automatic so this would apply differently to sticks, I am sure.

I noticed first of all the idle speed seems to be 8K rpm, checked a few Astras found this to be true. At just under 60 mph my rpm is at 2500 rpm. Using my Instant Fuel Mileage on the BCM it says I am getting at or above 30 mpg. When I go above 60mph, I am higher than 2500 rpm and my mpg is sequentially lowered.

So, from this I have deducted that easy on the throttle from 0-30 mph, then step on it (not floor it) till 60mph and I can maintain a healthy average of 30 mpg and still have fun on my way daily drive! 2500 is the magic number for my automatic.
The manual is at about 3000 rpm while cruising at 100km/hr (60mph), so how is it possible that the manual gets better gas mileage than the automatic? This I don't understand. Aren't manuals supposed to run lower on the highway?

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Old 10-24-2009, 08:30 PM   #40
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Default Re: 2500 - the magic number

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Aren't manuals supposed to run lower on the highway?
Nope, manuals typically get better mileage regardless of city/highway conditions. This is slowly starting to change though with dual clutch transmissions, which would be pretty sweet to get one from an Audi TT or A3 thrown into the Astra, paddles included!

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