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Old 07-27-2009, 08:41 PM   #1 (permalink)
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40mpg Possible in a 98 Buick Lesabre 3.8?

Well now I need to probe the group here.

My last 3 tanks of real attempts to hypermile on my 105mile trip to work have netted (per the scanguage) 35.5mpg, 36.8mpg and now 37.8mpg.

Sadly each tank had a massive amount of in town driving which blows in this car, I am lucky to break 25mpg in town, many times around 20mpg

Has anyone beat 40mpg in a buick? I can get 39-42mpg steady state on 5-10mile stretches of flat road so I assume it may be possible.

Sad part is DWL only works going DOWN hill, up I have to throw it out the window somewhat to prevent my car from reaching the magic 47mph as it starts wanting to downshift bad.

Any suggestions for in town? Acceleration still isn't masted here or maybe it just isn't possible.

Cheers
Ryan

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Old 07-27-2009, 09:33 PM   #2 (permalink)
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The 3800/4T60E can be both good and bad for FE. I have it in my 92 Trans Sport van. It will roll for a very long time and get good mpg, but under any load it is all over. I have gotten 28 mpg to work and back, and am positive I could get 30 downstate and back. I know what you're saying about the 47 mph barrier. There seems to be quite a large ratio difference between 3rd gear and 4th gear. 4th gear does not have much power for hill climbing (unlike my Celebrity which will climb mountain grades in 4th), and once it drops out at 47 mph, you might as well forget FE. Best thing I would do is try to keep it going faster so it does not drop out of 4th.

For the city, a little bump to get it going, then just let it idle to the next stop sign might be the best way to go. Dropping to N probably won't get any noticable gains, at least it doesn't with mine. There seems to be little to no engine braking with this powertrain. Anohter thing is I have never been able to get it to fuel cut, probably due to the lack of engine braking.

I have always wondered how well my powertrain would do in a vehicle that has much less frontal area and less weight. You might just have it. Also your Buick has a sleeker shape.

Sad to say how local driving kills great highway mileage. I know how it is. Last 2 times I have gotten over 40 mpg going downstate and back, then going to work and back till the tank is done makes me never get a 40 mpg fillup.

Just do the best you can. You're doing a heck of a job so far.
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Old 07-27-2009, 09:38 PM   #3 (permalink)
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in theory... sure... more likely if you made a long enough road trip that the car was already warmed up, filled the tank, drove your 47mph untill the tank was empty....
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Old 07-27-2009, 11:15 PM   #4 (permalink)
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I've come close several times. Best I've seen is 39.5 on the SG doing about 60-65 over ~145 miles. I did see a 38 mpg tank over 600 miles driving up I-95 earlier this summer.

~62 mph seems to be the car's sweet spot for 4th. It can climb hills just fine then.

In-town, get to 30 mph and back off, let the torque converter lock up in 3rd.
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Old 07-29-2009, 07:43 PM   #5 (permalink)
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Quote:
Originally Posted by 99LeCouch View Post
I've come close several times. Best I've seen is 39.5 on the SG doing about 60-65 over ~145 miles. I did see a 38 mpg tank over 600 miles driving up I-95 earlier this summer.

~62 mph seems to be the car's sweet spot for 4th. It can climb hills just fine then.

In-town, get to 30 mph and back off, let the torque converter lock up in 3rd.
I agree that 60ish is optimal for FE, except when there are tons of hills then lower works better.

I have been able to get around 35ish at steady state in 3rd but at around 35mph give or take. Trouble is any acceleration royally drops FE and coasting doesn't recover it all.

Too bad there isn't a manual transmission for one of these

Anyway I finally had a BAD highway trip to antigo, ideal roads but the car wouldn't cooperate, I was very lucky to average 31.2mpg on the scanguage for the in trip and 36.4mpg on the out trip. There were crosswinds and head winds which normally aren't a biggy but this time I just couldn't urge the car to get much more than 34mpg even going downhill.

With all the terrible in town MPG I will have mixed in thanks to my new job haveing me going here there everywhere I expect this tank to be dismal.

I am really missing my electric car that is still in wausau.

Anyone EOC this car? It seems that there is a method of flat towing it without the motor running continously, any ideas?

Cheers
Ryan

Last edited by rmay635703; 07-29-2009 at 08:01 PM..
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Old 07-29-2009, 08:00 PM   #6 (permalink)
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Hills I dropped to ~60 and ground it out. I found that much lower gets the engine out of its torque curve so it burns more fuel to go.

NICE-on coasting down the backsides works nicely. I also do a ton of NICE-on coasting in-town. Last fillup with 80% in-town driving was 23 mpg. Although I'm at a weak 18 mpg right now since my car's going to sit, and I wanted the internals all coated in Marvel Mystery Oil before it sits for about a month.

How recently have you drained/filled the transmission? They really like short intervals on the fluid. I noticed mine will shift to 3rd at 27 mph before I drained/filled it back at 30k miles, and that dropped to 24 mph very soon after a series of drain/fills.

Also, shutting the car off at lights is a mixed bag since it goes open loop for 10-15 seconds after you restart, negating the fuel saved by shutting it off for a short time.
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Old 07-30-2009, 12:22 AM   #7 (permalink)
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i'm jealous that you are almost matching my new civic. i really need to get that scanguage to see where i'm faulting.
best of luck with the 40mpg goal, that is also what i'm striving for.

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Old 07-30-2009, 10:10 AM   #8 (permalink)
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Highway only these cars rock. City is atrocious, for lack of a better word.

Went for a 30 mile drive to burn off the moisture/excess fuel in the oil before my car sits for a while, and did my usual DWL up hills and coasted downhill. Averaged about 34-35 mpg.

rmay, you can fabricate a nice-looking upper grille block out of lexan and toggle bolts, and do some aero mods to the front of the car, such as keep the air from hitting the lower control arms. Together they'll net you 2 mpg.
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Old 07-30-2009, 07:09 PM   #9 (permalink)
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Quote:
Originally Posted by nahtanoj View Post
i'm jealous that you are almost matching my new civic. i really need to get that scanguage to see where i'm faulting.
best of luck with the 40mpg goal, that is also what i'm striving for.
You would run circles around me in town though. My father has gotten as low as 13mpg in town during the winter if that is any indication.

The trouble is, even though in closed loop after a short while my fuel consumption always is almost double after a moderately cold start for up to 15 minutes. In the summer it seems to take a minimum of 5 minutes, usually longer before the idle fuel consumption drops and the car runs more efficiently.

The car really is intended as a road car and not a town going vehicle.
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Old 07-30-2009, 07:25 PM   #10 (permalink)
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That's what I did for a grille block. It works wonders for warmup times. Right now I'm running with the lower half of the right side chopped off. Still somewhat aero, and actually enhanced my cooling, go figure.

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