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candak
Dodge Dakota
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10/14/2005
08:33:42
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 Subject: gears and mileage
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Message:
Hi guys- as I was taking my trailer up hills on the highway I noticed that when I'd turn the OD off and 3rd kicks in, I have to back off the gas pedal to keep the same speed I had when I was in OD; my question is this: am I using more fuel in OD at 2000rpm at 100KMH up a hill loaded or in 3rd at 2600rpm at 100KMH with a lighter foot on the pedal? Probably an obvious answer to some. I'm just curious. I know it's better for the engine and tranny to be in third, though. The Dak is a 91 5.2 open diff (not sure the ratio).
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Mikes99Dakota
GenIII
10/14/2005
09:42:09
| RE: gears and mileage
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Message:
Depends I guess, maybe if you left it in O/D and see if it was going to downshift?
If it downshifts then keep it in third if not, you wil prolly have better mileage with it in o/d.
1999 RC Auto 5.2L
Mopar PPH, Magnaflow 3" w/cut-out, 3.90s/Suregrip, 50mm Fastman TB
Track Times:
9.47 @ 72.21mph
14.89 @ 91.33 mph
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davec
Dodge Dakota
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10/14/2005
10:00:29
| RE: gears and mileage
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Message:
I would imagine you would use more gas at 2600rpm than you will at 2000rpm. It takes more fuel to run the engine faster. There is the load factor (uphill), but I don't think it would come into play here. If I'm going uphill at 2600 or on the flat at 2600, the engine is turning the same speed regardless of load. But what do I know.
Your ratio, is probably 3:55. You should have a label (I'm thinking in the glovebox, but not sure) that lists your gear ratio.
How heavy is your trailer and do you tow often? If so, I'd be looking into an aftermarket cam for that beast.
Dave
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99DAK
Dodge Dakota
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10/14/2005
10:49:40
| RE: gears and mileage
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Message:
"If I'm going uphill at 2600 or on the flat at 2600, the engine is turning the same speed regardless of load."
You WILL be using more gas going uphill to maintain the same speed/rpm as on level road (assuming TCC is locked).
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davec
Dodge Dakota
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10/14/2005
12:50:46
| RE: gears and mileage
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Message:
Thanks 99DAK. I'm not sure what I was thinking.
Obviously the engine would be working harder to maintain 2600 uphill than it would on the flat. Which in turn would use more gas.
Been a long week, sorry guys.
Dave
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Kowalski
GenIII
10/14/2005
15:40:00
| RE: gears and mileage
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Message:
It's possible that you could be using less fuel at a higher rpm in third if the engine is more efficient at higher revs. Several of us have noted that with the 4.7 too. I was skeptical of people claiming higher milage with OD off til I went from 3.55 to 4.10 gears; saw a slight gain in mpg now even though running higher revs.
Lead, follow, or get out of the way
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