HOW to drive the 6.5L with Automatic Transmission- "D"/Overdrive or in "3"/3rd Gear

[Jochen Woern]

Hello All:

I was wondering what would be the best way to drive the 6.5L Turbo Diesel with Automatic Transmission on an average around town:

- "D"/Overdrive?
- "3"/3rd Gear?

I would like some input in regards to the three (3) major factors:

- Power/Performance
- Fuel Economy
- Longevity of the Engine, what is best for it?

It is clear that one should always drive in "D"/Overdrive at higher speeds on the freeway. However, I find that I do not get enough power at lower speeds in city driving conditions if I am driving in "D"/Overdrive.

Any input from all of you would be appreciated.

Have a great day,
Jochen Woern

[Robyn]

Normal driving is usually done in the "OD" position.
There should be no difference in the trucks power or performance around town when switching from D to 3
The transmission will not shift into lockup until approx 45 MPH in OD and it will also lockup in 3rd at a similar speed.
If there is a noticeable power difference then there may be an issue with the transmission.

I hardly ever run my dually in anything other than the OD position except when towing or possibly on a steep downgrade I may drop it to 3 or 2 for braking effect

Good luck and let us know

Robyn

[DA BIG ONE]

Have you recalibrated your vssb for the larger than stock dia tire, or? Your 4.10 rear ratio is now taller by the difference in dia of tire meaning you are going faster that speedo says if not recaled..OD and lockup is now slightly higher too.....

I run 3.42's w/33" dia tires and that gives me really tall gears under all situations. I can drive in 3rd only and get lockup @58+ mph w/same rpms as if I was running stock sized tires and 4.10's I do this up to say 62mph w/o issues.

[chickenhunterbob]

"OD" to go ahead, "R" to back up.

[a5150nut]

"OD" to go ahead, "R" to back up.

I'm sorry. I thought I closed the door on coop..............

[Cowracer]

Just to clear something up.

OD is not some additional "thing" that kicks 'in' or 'out' depending on where the gear lever is. It is simply the 4th gear.

In mecanical terms, for the longest time, high gear in most cars was direct drive, or in other words a 1:1 ratio. For each revolution of the input shaft, you get exactly 1 revolution of the output shaft.

Since the late 80's, in an effort to reduce fuel consumption, most cars and trucks have offered a high gear ratio greater than 1:1. In the 4L80e, the high gear is a 0.75:1 ratio, or for every 3/4 of a turn of the input shaft, you get 1 full turn of the output shaft. The output shaft is overdriven, hence the term. Gears 1-2 are still underdriven, and 3 is still direct drive. All placing the selector in 3 does is prevent your truck from shifting into 4th.

I dont know where it started from, but a lot of people think that if you run in town in OD you will burn up OD, or the engine or something. This is utter nonsense. The only way it hurts is IF you are loaded heavy, and IF your rpms are too low, you may not have enough ATF pressure to ensure the bands are locked up tight. I think too low is around 1700 rpm, by the way.

So look at it this way, on any old non-overdrive car would you run around the city in 2nd thinking you would save fuel, or increase the life of the engine? If not, then why do it with an OD tranny?

Tim

[DennisG01]

Just to clear something up.

OD is not some additional "thing" that kicks 'in' or 'out' depending on where the gear lever is. It is simply the 4th gear.

In mecanical terms, for the longest time, high gear in most cars was direct drive, or in other words a 1:1 ratio. For each revolution of the input shaft, you get exactly 1 revolution of the output shaft.

Since the late 80's, in an effort to reduce fuel consumption, most cars and trucks have offered a high gear ratio greater than 1:1. In the 4L80e, the high gear is a 0.75:1 ratio, or for every 3/4 of a turn of the input shaft, you get 1 full turn of the output shaft. The output shaft is overdriven, hence the term. Gears 1-2 are still underdriven, and 3 is still direct drive. All placing the selector in 3 does is prevent your truck from shifting into 4th.

I dont know where it started from, but a lot of people think that if you run in town in OD you will burn up OD, or the engine or something. This is utter nonsense. The only way it hurts is IF you are loaded heavy, and IF your rpms are too low, you may not have enough ATF pressure to ensure the bands are locked up tight. I think too low is around 1700 rpm, by the way.

So look at it this way, on any old non-overdrive car would you run around the city in 2nd thinking you would save fuel, or increase the life of the engine? If not, then why do it with an OD tranny?

Tim

Well said, Tim. Another way to look at it: If the tranny is constantly upshifting/downshifting while at a relatively steady speed, you're in too high of a gear. Either speed up or select a lower gear. You should also downshift if the engine is "lugging" (this is what Tim was talking about in his 4th paragraph). Besides, the enigne actually operates more efficiently in a slightly higher RPM band.

It has taken me YEARS to convince my father that when he is towing, he should keep the RPM's in the 3,000 - 3,500 RPM range (350 gasser). For some reason he kept insisting that it was better to have the RPM's as low as possible. In fact, rather than give it a little gas to keep his speed up, he would let the speed scrub off to the point where the converter unlocked and it eventually downshifted by itself. I explained time and time again about higher tranny temps and more stress on the engine, but it wasn't until he rode along with me (while towing) and I showed him what was happening on my gauges at varying speeds. He's still reluctant, but getting better.