07 1100rpm cruise with 68rfe auto?

[Lorenz]

New to me truck.



The 2007 6 speed auto seems to lug the engine a lot more than my 03 48re auto. On a gentle cruise 40-50mph I saw 1100 intermittently. This can't be right?

 

[HBarlow]

It probably has the undesirable 3. 42 differential gears (unless it is not used for much towing. ) Coupled with the very tall second overdrive of sixth gear range of the 68RFE that's about what to expect.

 

[subodh]

lock tc in a lower gear?

 

[Jim W]

In city driving I tend to use the manual sift toggle switch on the wand for the transmission selector. Since the speed limit is usually under 40 MPH. I will keep the 6 spd auto out of 5 and 6 gear range. This keeps the truck in the 1800 to 2000 RPM range were I like it. I will let the truck shift normally and not use the toggle switch only on the highways. Where I can use the overdrive and double overdrive to keep the RPM's in the 1800 to 2000 RPM range. My gear ratio is 3:73.

Jim

 

[Bob4x4]

Sean,with a light enough load that will be normal,even my old 05 does pretty much the same thing. I wish I had your paddle shifter...

 

[Lorenz]

3. 73

I remember reading in my old manual not to "lug the engine". 1400 rpm and below was lugging. This is gonna take some getting used to.

 

[Lorenz]

My '03 would jump ship on its own, and downshift when it saw 1400-1350 RPM under an easy load/ no load.

How do you think longevity is effected with the 68rfe acting like this? It sounds great for MPG, but this behavior has to be hard on the OD units and the trans in general.

 

[Bob4x4]

I haven't seen a single 68 failure on a stock powered truck yet,that says a lot in my book.

 

[dlmetzger]

I've been curious about how low rpm on the 68RFE auto will go while driving the truck around town. My engine will lug down to 1100 rpm in sixth gear (which is 44 mph) with no load. I would think Dodge is well aware of the limits on the Cummins engine.
I've read on the Cummins site that they suggest that the rpm be kept at 2000-2100 for the best mileage. I'm guessing the difference is that Cummins is speaking to an engine under load.

 

[Hoefler]

If the load is light or non-existent, you are not lugging it. The transmission and the controller will not let you lug it. Just put it in gear and go. If you run in tow/haul mode, it will shift before it gets that low.

 

[Lorenz]

Thanks guys.

Reflashed today and brought everything up to the latest and greatest... No difference in the shifting department. It does idle a bit smoother.

 

[gsbrockman]

My $0. 02 take on the matter is that the lower rpm's create higher EGT's that will in turn keep the particulate filter a little hotter to burn off any soot.



Truck in my signature is at 48k miles and hasn't regenerated since 21k miles :-laf

 

[daverobb]

My truck is 3. 73 rear gear equipped. At 100 KPH (62 MPH) the tach reads 1600, at 110 KPH (68 MPH) it reads 1750 and at 120 (74 MPH) it reads 1900 RPMs. These would be in 6th gear.
In town, I never let the transmission shift higher than 4th. This keeps the 6. 7 in or near its sweet spot and helps keep the DPF clean. I always run the E-brake.

 

[Cosmo]

H&S Overdrive

Look it up. The difference is amazing. Instead of shifting up as soon as possible in every gear (6th at 40mph is asinine) it holds gears to keep the engine in a more efficient RPM range.

As far as fuel economy goes, my daily commute is about 10-12 miles each way, 5 miles of 70mph freeway and the rest is mostly 45-50mph surface streets with stoplights. I average about 17 mpg, and I'm never mad at my trans for being in the wrong gear anymore.

 

[mxaaron]

It probably has the undesirable 3. 42 differential gears (unless it is not used for much towing. ) Coupled with the very tall second overdrive of sixth gear range of the 68RFE that's about what to expect.

If by undesirable you mean better fuel economy, and lower rpm highway cruising, than yes it is very "undesirable. "



However if you tow trailers 10,000 lbs and less, the 3. 42 is quite adequate with the power plant our trucks have.



To the guy who say's he's at 1900 rpm at 74, unless the auto is quite a bit taller than our manuals (and maybe it is... . ) it sounds like you might have those "undesirable" gears too.

 

[mxaaron]

3. 73



I remember reading in my old manual not to "lug the engine". 1400 rpm and below was lugging. This is gonna take some getting used to.

1500 produces the max torque rating. I don't think 1400 is lugging. (Certainly not unloaded. )

 

[Cosmo]

1500 is max torque, but that's at WOT. Simply cruising part throttle it may not be as efficient as higher up in the RPM range.