Well I just got back from a 600 mile round trip towing a 25ft travel trailer with a loaded weight of about 7,200lbs. I noticed a few things of concern during the trip.

1. At an average speed of 60mph I only acheived a whopping 8.5 mpg....I guess I expected a lot better than that considering that when the truck is empty I get almost 22 mpg on the freeway.

2. When accelerating hard up a hill at about 60 mph I hear a loud whining sound that fades away at 64-65, the noise gets louder the longer and steeper the hill is when I stay at that speed.
I also notice a different pitched whining sound from 28-40 mph when there is no load. (I know it's not the turbo. This is a MUCH louder sound that resonates through the whole cab.)

3. I had to manuever the trailer though some rough/muddy spots so I put the truck in 4lo. While in that position everytime I went from drive to park the tranny would grind. Also while in drive if I hit the brakes too hard there would be a grinding sound.

4.Lastly, the Tow/Haul mode works great about 85% of the time. However when I got to winding hills where the speed and pitches vary alot the tranny felt like it was lost. It is way too happy to drop into overdrive and then when in downshifts into 3rd I don't feel like I am getting a solid connection between the engine and tranny like I should be.. I.E. the engine is reving hard and fast but there is little accleration. I really felt like the truck was going to fall flat on it's face at times...

Overall I love this truck but these few things have me a litte concerned about the longevity of it being used as a recreational tow vehicle. Any thoughts would be appreciated. Thanks.


P.S. I have 9,000 miles and no mods except for pyro, tranny and boost gauges.

 

I have had the same concern about the 4lo thing with mine. I tow with mine about 95% of the time (it is my job) I tow 10k empty and average 10k load. When shifting from park to reverse or vice versa it will grind because there is so much torque on the trans/transfer case. I found that it is best to shift first into neutral then a quick shift to park or gear. This lets the trans shift with no load on it. As for the other things I have never had a single problem like that so I have nothing to input. sorry man!!

 

That mileage sounds low, but I've also never towed anything that large with my truck. I got about 13.6 with the cruise set at 70 mph towing a 3/4-ton extended cab long bed Chevy truck on an open trailer (total trailer weight ~7000 lbs, I'm guessing) when I had the same number of miles as you do, so your mileage may not be too far off. Your mileage WILL improve as you rack up the miles on the truck.

Your turbo will be working harder when towing than when not, and that may have something to do with the sound. As far as the falling flat on its face, keep in mind that you're towing a rather heavy load. On an uphill, your engine temps will increase. The computer in the Cummins will start cutting power as your temps increase to reduce the possibility of overheating and protect the motor. This is a good thing, but it may be the cause of what you're describing. The fact that you have the automatic only makes matters worse seeing as the automatic will always create more heat for your cooling system to dissipate. That said, you may have a problem with something and it might be a good idea to bring it to the dealership and see what they say.

I can't give you any advice on the 4x4 or the auto tranny being lost... I have a 4x2 and a 6-speed, and I love it!

Good luck!

 

i second the neutral then park shift, i have done that for years on all of my 4x trucks. it just lets everything slow down and takes the load off.

 

My 04.5 used to give me 10MPG on a good day with the 10K 5er behind it. It was equiped with the 48RE. My new 05 with the 6 speed gives me 12.4 on a regular basis over the same route. It seems to me that the noise may be the fan as it comes on and off. Also, if I remenber correctly the fan is variable speed. The harder it works the more noise it makes. I don't get any fan noise with the 6 speed as there is no tranny cooler in front of the radiator. You might see if there is any corralation between your tranny temp and the noise.

Check the bug line on your TT. If it is very low on the front, you may be getting a lot or drag from the trailer. A solution to that would be a cap for the truck bed. Anyway, enjoy and spend more time in the hills with the trailer.

 

#4: Sounds like you're used to having the torque converter locked-up and when it isn't, there's a lot of slip (engine revs up but, the power does not get transfered to the wheels).

I'm not trying to make you feel bad but, I have a travel trailer that weighs 7000+ lbs and, on a number of occasions, at 55-57 mph. have gotten 15 mpg's on flat land with no head winds. 14 mpg's at 60-62 mph. 13 mpg's 70-75 mph. 8.5 mpg seems low. It might not be a bad idea to get your truck checked-out.

I hope you get it working the way you want.

Joe F.(Buffalo)

 

I too agree its low. I towed same weight 500 miles last weekend and averaged 14mpg (steel 20ft tandem trailer with CJ7 lifted Jeep, 2 ATC's, and 4 coolers). I have the nv5600 and 285 tires with speedo corrected though.

However, I get like 18 unloaded which makes me think there is something wrong. Going from 22 to 8 mpg? Something else is going on.

 

I just towed 10k lbs over CA HWY 395 from Bishop to L.A. (lots of inclines) and averaged 9.5mpg. Mine has nearly twice the miles as yours and still seems to be improving with use. 8.5 seems a little low, but if your terrain was more extreme, that could account for it. Then again, the only time I can ever get 22 empty would be downhill with a tailwind.

Power-wise, my bone stock CTD pulled at least as well as my much lighter 2wd PSD 7.3 did with the Hypertech PPIII programmer installed.

Sorry, but I don't have the T/H problem you do because my 04.5 48RE stays out of OD in T/H and you can feel when it locks up. Why they saw the need to change this for 05, I don't know.

I concur that one of the sounds you're hearing could be the cooling fan. Until I figured out what it was, I thought I was hitting rough patches in the road (like the roar of tire noise) except the road visibly didn't change. Then, it occurred to me that it only happened in the heat of the day on long uphill grades . . . duh!

I use 4LO for maneuvering my fiver into its storage space (up over a curb onto a horse trail up and onto the driveway). It lets me do it ssssslllllllloooooowwwwwwlllllllllyyyyyy. I, too, noticed that engaging the tranny in 4LO kinda slams in. I like the idea of going thru neutral . . . I'll give that a try myself. I already discovered going thru neutral to switch from 2HI to 4LO works very well.

 

I agree but disagree with most of you about the low mileage. First what is the frontal area of your TT???
This make a big difference in fuel mileage, more so than weight will. If you pull a 500lb barn door behind your truck so that it catches all of the wind your fuel mileage will be real low, however if you pull a 10k enclosed car trailer that is the same or less height as your truck your mileage should be the same or better. It all has to do with wind drag, the less drag the better mileage
You may actually need to increase your speed by 3-5 mph to get better fuel mileage. As someone did say, check your bug line and see where it is on the trailer. You may need to increase speed just to get the truck up to it's happy zone for pulling also.
What was your rpms when pulling at those speeds???

More info about your truck would help also?? What is your gear ratio?? 3.73 or 4.10?
These can make a big difference in your mpgs.

Now NOT to make you feel bad I pull 5vr at 63-70mph and get 11-13mpg all the time. I have seen a few occasions at 8.5 mpg, possible bad fuel. This has been during my current cross country trip, lots of mountians to deal with.

 

i think if you went 70mph you would get better mileage

when you are at 60mph you are at around 1600 RPM. now thats where the torque is, but at a lower RPM the engine is working to keep the load moving. When you are at 70mph at almost 2000RPM the engine isnt having to work so its not lugging at all and having no problem pulling that, and the mileage would go up.

Up mountain passes unloaded i get better mileage at 80 than i do at 55 because at 55 im pushing 1500 RPM lugging the engine

now thats if you have 3.73's of course.

 

At 60mph, the wind shouldn't be bringing him down to 8mpg.

At 80mph, the wind would have a large effect.

I could pull a 20x20 barn door at 80 and get better than 8mpg.

 

Thanks for the replys.


I have 3.73 gears.

The whining sound could definitely be the fan as the clutch engages, it makes sense being that the noise changes with the RPMs. Althought I have never heard a cooling fan that loud before.

In regards to towing at 70 mph. I would love to get improved mileage but I am not willing to pull a TT faster than 65. I have seen many accidents with trailers and that extra 5 mph can make a big difference in safety. Thanks for the suggestion though.

I think for the time being I am going see how the next few trips go and if things do not improve I will take it in to be looked at. I REALLY REALLY wish that Dodge or some aftermarket company would come out with a way to change the shift patterns for the tranny though. Overdrive lockup is WAY to early in Tow/Haul mode, 60 mph lockup would be nice that way in the hills I wouldn't have to worry about "hunting" It is pretty irritating to be climbing a hill and hit a brief flat spot so it immdiatley shifts into 4th, then 300 ft later your at a hill again and need to downshift........oh well can't have it all I guess. I sure do love the Cummins motor though!!!


J

 

Your owners manual tells you to always put the truck into neutral or park before shifting into 4LO. Now you know why.......

 

Do your best to keep your rpms up as possible especially on entrys of hills, if your using cruise it wont realize your on a hill till your already there and losing mph and rpms, along with mpg. Diesels have a different power range than it sounds like your used to and when your in over drive tring to stay at one speed your gonna lose. Especially with 3.73s. Work with it a little bit and you should see a noticeable difference after you get used to it.

 

Thanks, but I know how to get INTO 4lo. What I was saying is once I was in 4lo there is griding while shifting between gears and also while the truck was going foward if I hit the brakes pretty hard there was also grinding. Something funny is going on there.



J