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Which is better for fuel economy? I notice that when cruising at ~50-55 in D5 RPMS are well below 2000rpm, which is not always good for mileage. Should I trow it into D4 or not?
 

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I always leave mine in D5, as the lower RPMs usually equates to better fuel economy.
 

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MomsMDX said:
Which is better for fuel economy? I notice that when cruising at ~50-55 in D5 RPMS are well below 2000rpm, which is not always good for mileage. Should I trow it into D4 or not?

D5 all the time D4 for stop and go traffic, like in Downtown.
 

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Look at your instantaneous mpg readout; on mine, it almost always shows better mpg the higher the gear. Using Cruise Control to maintain your speed, shift back and forth between D4 and D5 to see which gives you better mileage under what conditions. The meter isn't dead-accurate, but it gives a good indication.
 

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Lower rpms = Higher mpg

I would keep it in D5 unless it begins downshifing on its on a lot.

In hilly terrain, in D5, it may have to downshift a lot to get up the hills. By using D4 in hilly country the transmission does not have to work as hard. All D4 does is make the 5th gear unavailable at high speeds.
 

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Here is my understanding (correct me if I'm wrong please)

P ........ i'm done, sleep well, beauty (no mphs)
R ........ go back, I forgot my valet, duh!!! (0-20mph only!)
N ........ this doesn't look good, a tow truck??? help!!! (no mphs)
D5 ...... step on it, lemme hear those 6x RPMs (good anywhere) (10-17 mphs city, 18-21 mphs highway - well don't expect high numbers if you keep listening to the revving engine!!! :D)
D4 ...... step on it, but remember how expensive is gas (usually skip ;))
D3 ...... step on it, i'm on the highway - LOOK OUT PEOPLE!!! (loose those 4 & 5 gears, who cares about those 22 mphs, we get 18 and are pretty happy with it, right? ;))
2 ........ step on it (GENTLY), it's wet/snowy outside (or a very slow stop-n-go traffic), cause she stops faster (0-40mph)
1 ........... do not step on it at all, lemme get u out of that hole or ice skating ring (better press that VTM Lock and keep your speed under 18mph!!!)

my habbit is to switch to 2 from D5, when traffic slows down and then back to D5 when traffic frees up (during rainfall mostly); that may be another reason why i do not get highter than 18 mph, but the truck is more responsive that way and easier to slow it down.
 

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Why would a higer RPM give better fuel mileage, doesn't make sense to me. Just more friction and heat going to waste. I also cannot think of any harm being done by cruising at 1500 to 2000 rpm, I would think that is ideal for cruising and maximizing gas mileage. You lose torque at the lower RPM, but the MDX does have a rather flat torque curve.

I would imagine that 99.999% of the time, D5 is the way to go. As for as engine breaking -- cheaper to replace breaks than to put more wear and tear on an engine by downshifting to slow down.
 

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weth,

As a past-owner of weird cars, I owned a '63 Studebaker Lark 4-door, 259 V8, 3-speed with overdrive (bought new). The overall gear ratio at cruising speed was so numerically low when in overdrive that the engine was close to lugging; I consistently got 2 mpg better mileage with the OD locked out. My favorite shift pattern was 1, 2, 2-OD, 3-OD. I was younger then, of course.
 

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D5

D5 with the overdrive engaged!:2:
 

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paul123 ... What if I want D5 without overdrive?

:16:
 

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if you drive on the highway or straight streets, D5 is 100% a way to go, but you would be killing your tranny much more if you go uphill on D5!!!!! on the wet or snowy surface, D5 is an overkill - you do not need the momentum created by shifting gears that make your suv 'dance' on the road... i care less about the breaks wearing out faster or not, but i noticed that suv handles much better when in D2 during heavy rain and going at less than 35 mph...

example... you end up on the piece of icy road and you are going at 30 mph and you see a stop sign at 200 feet, you going on D5. what would/should you do then?
 

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I certainly have no reservations moving the shift lever to meet road/speed conditions. There is alway too much of a good thing. But the biggest factor to keeping it in a lower gear than necessary at a reasonable speed, is gas mileage. Proper manual shifting is not putting undue wear of the transmission. Just think of all the shifting it does on it's own during normal driving, especially in commute traffic.
Speed shifting, excessive downshifting instead of proper braking when approaching a stop, throwing it into reverse while the vehicle is still rolling, not warming up your vehicle before driving it hard, and poor maintenance are the real tranny killers.
 

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srpbep said:
paul123 ... What if I want D5 without overdrive?

:16:
D5 will automatically put you in overdrive at correct speed.
 

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Overdrive

Wait a sec, just went out to the Acura web site and looked up the drive ratios:

1st 2.563
2nd 1.552
3rd 1.021
4th 0.727
5th 0.520
Reverse 1.846
Final 4.428

Doesn't this mean that Both D4 and D5 are overdrive???
 

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Re: Overdrive

srpbep said:
Wait a sec, just went out to the Acura web site and looked up the drive ratios:

1st 2.563
2nd 1.552
3rd 1.021
4th 0.727
5th 0.520
Reverse 1.846
Final 4.428

Doesn't this mean that Both D4 and D5 are overdrive???
When driving in D4 it will not kick into overdrive, check it out on the parkway, when in D5 you will notice the rpm's drop at a certain speed while in D4 it will not drop into the lower rpm.
 

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overdrive vs "overdrive"

In "olden times" overdrive meant "small auxiliary gearbox that provides additional gear ratio(s) by means of a selectable secondary final drive ratio".

Now when manufacturers talk about overdrive they just mean "drive shaft turning faster than the engine crankshaft " .
Thus BOTH D4 & D5 see the driveshaft "overdriven" relative to the crank.

Revs drop MORE in D5, but they will STILL drop in D4 compared to D3 and steady state speed.
 

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Just outta curiosity, how does the torque converter lockup play into this, if it does at all?
 

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paul123:

A lot of that "rpm drop" that you mention is due to the torque-convertor lockup -- the convertor is bypassed by mechanical lockup piston(s) to further improve gas mileage. That can occur in D3, D4 and D5, and it disconnects before any gear-shifting is done. It's controlled by the Powertrain Control Module computer, and you can't do anything to affect its operation. The service manual states that the lockup mechanism operates in 2nd, 3rd, 4th, and 5th gears, but not in 2nd if the gear selector is in the "2" position.
 
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