Lugging my CTD??

[alexanderJ]

I pull a 6000 lb travel trailer and usually drive around 60 mph on the highway, frequently dropping down to 55 mph on country roads. 60mph is just a hair under 1600 rpm. I get the feeling I may be below the torque curve and lugging my CTD.



Since I can't lock out OD on my '05, is my only answer to speed up?



Looking at the overhead, 60 sure gives better fuel milage than 65 or 70mph. I know the overhead is usually generous but would I actually get not only better performance, but also better fuel milage at say 1700rpm?



I still can't undrstand why DC decided the '05 would be the only year they would not allow OD lockout.

 

[CUMMINZ]

Running your CTD at 50-60mph is a perfect time to run it in tow/haul mode.

 

[jimnance]

You are at the bottom end of a very flat torque curve. Being at peak torque is the ideal place to be from a performance point of view. On a hill you want to be higher on RPM to generate more work via the extra horespower you will make. On the flats you are perfect, IMHO.



Tow haul will decide if you need another gear. Admittedly, sometimes I'd chose a slightly different spot for the shift, but it does a pretty good job considering it's a four speed auto.

 

[GaryCarter]

It's not lugging unless you don't have enough torque to increase speed; not the case on flat ground. My truck is quite happy down to about 1400 RPM in OD with tow/haul on.

You are never going to lug an auto (stock) because it will downshift before you ever apply that much torque.



Gary

 

[alexanderJ]

Thanks for the replys. I always run in T/H mode when the trailer is hooked up. It appears based on the comments I need to let the computer decide what gear I need/will be in. So far I've been comfortable with that and don't feel any particular strain on the truck. I need to add some gauges to check egt/boost and maybe that will tell me if there is an issue with my speed.



I know that probably 90% of the CTD's pulling trailers have no clue as to what's going on with their engines, so I'm not sure, based on my light load, if I need to be concerned either. I just want to make sure I'm not doing anything tyhat could be corrected, but on the other hand, I'm not sure what control I have with the '05 48RE.

 

[GLASMITHS]

Thanks for the replys. I always run in T/H mode when the trailer is hooked up. It appears based on the comments I need to let the computer decide what gear I need/will be in. So far I've been comfortable with that and don't feel any particular strain on the truck. I need to add some gauges to check egt/boost and maybe that will tell me if there is an issue with my speed.



I know that probably 90% of the CTD's pulling trailers have no clue as to what's going on with their engines, so I'm not sure, based on my light load, if I need to be concerned either. I just want to make sure I'm not doing anything tyhat could be corrected, but on the other hand, I'm not sure what control I have with the '05 48RE.

Maybe you should talk to a transmission guy about cooler flow at that low rpm.

 

[JERRYKAM]

I also tow a 6000lb (loaded) TT. I live in CO and most of my towing is above 8000ft. Operating in Tow/Haul generally provides acceptable shifting, however there are times when I wish the transmission would remain in 3rd gear a bit longer before upshifting to 4th. When pulling a fairly long steep grade at 50mph or so the transmission will downshift to 3rd and stay there. But as I slow to 30mph for a curve it will typically upshift to 4th prior to coming out of the curve. As I accelerate back to 50mph unless I press the accelerator almost to the floor the transmission tends to stay in 4th. My standard practice in this situation when I want to down shift without hitting the throttle, is to simply press the tow/haul switch three times (quickly). This recycles tow/haul back into 3rd...



As you have stated, Tow/Haul is not perfect but it does a reasonable job of shifting when necessary, what good is an auto trans if it can't shift properly. Thats why we bought a truck with an auto in the first place.



Now for the problem. I have a Trans temp, Boost and EGT gauges installed. When climbing as noted above any time the trans upshifts to 4th and I begin to accelerate out of a curve EGTemp will skyrocket. 1300deg in just a few second. This is my self imposed limit at which I recycle tow/haul to get back into 3rd or manually dropping into 2nd.



Prior to installing gauges I would simply let the transmission do its thing. Only occasionaly dropping into second if I felt the engine required a bit more RPM. Ignorance was bliss. Now I have come to realize EGTs can easily exceed 1300deg I'm a lot more attentive to what temps are doing.



As a side note when pulling in 2nd gear, TC unlocked, EGTs are fine but the trans temp will quickly climb to 250deg plus (my gage only goes to 250deg) and the probe is on the torque converter discharge line which is where the highest temperatures are generated.



Keep in mind I'm towing a relatively light trailer, and my truck is stock. I can only guess what the temps would be if I were towing a heavyweight 5th wheel.



I have posted an inquiry to Cummins requesting a clarification as to what the max EGTs the CTD is rated for. I have been told by my dealer that it is rated for 1250deg continuous. I have heard from other sources that it is also rated for 1500deg short term. Of course no one seems to know what "short term" translates to in minutes.



Assuming Cummins responds to my inquiry, I'm not holding my breath, I will post their response

 

[GaryCarter]

Jerry, you can try putting your selector in second when running in that gear for prolonged periods. With my 2005, that will make it lock up in second. Don't know about your 2006.



Some people have told me theirs lock up in second with the selector in OD, but the service manual for mine specifies selector in second for second gear lockup.



YMMV.

Gary