Hi guys
I have a 2010 dodge 3500 diesel with auto and 3.73 rearend
Our trailer is a 2012 fuzion toy hauler.
We took a trip a few days ago to GA and then to Alabama.

We stopped at the cat scales and here is the weights
Steer axle 5,100 Drive axle 6,440 Trailer axle 11,700

Gross weight 23,240 The best MPG I could get was 9.1 and that is running at 60mph dose this sound right or should I get more. I used the tow/haul mode but it was always a hard shift going up the hills.

Ron.

 

how are you measuring your MPG? using the onboard display?

I tow an 11k fiver and am getting in the 12.5 range hand calculated..

 

Yep the onboard display. Maybe next time out I will try the hand calculated way.

Also should I use the tow/mode? Was running around 60mph and rpm were around 1,500 Going up hills the truck would shift down rpm 2,100 or so then after the hill back to 1,500 A few times the truck would shift real hard going up the hills.

Ron.

 

Well, I'd say yes, but my Tow/Haul behaves differently than yours.. I can't lock out OD... plus you have a 6 speed 68Re vs my 48RE 4-speed.

I leave my Tow/haul on when towing and usually set the cruise control to about 65 in the flats, and 55 in the hills.. I use the gas pedal to kick it down to 3rd gear when going up steep grades if it starts to lug a little.

 

Yours has a gas pedal?? What for??

 

well it sounds better than Diesel pedal... I suppose I should call it a throttle.. ah.. who knows..

 

I took it as just having an "on/off switch"...

 

Ron;

Your Grossed combined weight is about the same as my rig. My Steer Axle is 4700 lbs and Axle is 7280 lbs Trailer 11,480 lbs or Gross Combined 23,380 lbs

My normal fuel mileage hand calculated is 11.3 to 11.9. One time on a trip from Gloucester Va to Charleston SC coming down 95 I got 12.7. Good Fuel.

It's my opinion, you do not have enough RPM's at your towing speed and enough HP/torque, to maintain that gearing. Hence the down shift and hard up shifts. The hard up shift is probably the increased pressures in the tranny that are created when running in the tow haul mode. The other part about the hard upshift is most likely when in 5th gear, the torgue converter is locked up and remains like that when it shifts into 6th. You'll get a hard bang.

Since the 68RE has two overdrive gears 5th and 6th, I would be towing in 5th when in the hills. This should elimanate the downshifting unless you come up on a 7% grade. Your truck is rated at 650 ft/lbs of torque.

Here is short mph/rpm chart using your tranny in various gears.

Gear 1 2 3 4 5 6
Ratio 3.231 1.837 1.410 1.000 0.816 0.625

RPM
1000 8 14 18 25 31 41
1100 9 15 20 28 34 45
1200 9 17 22 30 37 49
1300 10 18 23 33 40 53
1400 11 19 25 36 44 57
1500 12 21 27 38 47 61
1600 13 22 29 41 50 65
1700 13 23 31 43 53 69
1800 14 25 32 46 56 73
1900 15 26 34 48 59 77
2000 16 28 36 51 62 81
2100 16 29 38 53 65 85

So if you towed in 5th gear at 60 mph you'd be around 1900 rpm. Cummins says you should avoid rpm's less than 2100 when towing a max load for fuel mileage and load handling. Running in 5th gear at 1900 is close to a 4:56 rear ratio in 6th gear.

My truck has a 48re. I changed gearing from 3.73 to 4.10, added a triple lock torque converter, tranny mods, to reduce the load on the tranny when towing from 76% load with the 3.73's to 54% with the 4.10's towing my rig in OD.

Read my sig for other stuff. Anyway, headed up the turnpike, north of Orlando with the 3.73's and 4.10's at my towing speed which is 62 mph, I would get a down shift with the 3.73's (low rpms) and once and awhile with the 4.10's.
(200 rpms more with the 4.10's) If I increased the speed and rpm's on the same road with the same tow, never get a downshift. So running stock engine, with higher rpms does make a difference.

I have a Juice with the Attitude Controller. When I put that in the tow mode it increases the torque to 730 ft lbs (advertised) Thats 80 ftlbs more than your engine. Mine will not downshift when in this mode. EGT's will slowly reach 1300 if towing up a long hill at tow speed. If I increase tow speed EGT's are no longer an issue as I'm moving more air thru the engine.

So, I'm not saying you need more hp or torque just a little more rpm. Your fuel mileage should not change much since your going to be 5th with the downshift anyway.

Sorry for the long post.

After posting I saw the chart was jammed up. The numbers to the right of the rpm's is the mph at that RPM for each gear.

Dave

 

Thanks for the info guys.
I will try to keep the rpm's up when towing.

Was just scared when I would down shift to 5th and it would go up to 2,100 or so. How long can I tow in 5th? and just use it on the hills?

When we were towing it was around 109 outside and the truck temps motor was around 210-215 Transmission was 170-185

Should I look about getting a biger pan for the transmission or just leave it all stock?

Thanks Ron.

 

Ron;

Don't think it will hurt the tranny towing in fifth gear. You may see a slight increase in MPG just because you've taken some of the load off the engine.

Your tranny temp seems to be really cool, like not as hot as I would expect with the engine at 210. With my rig, my tranny runs 100 degrees above abient
temp. So if its 90 ourside its 190 or 192. It don't matter if I'm towing or not. A couple years ago runnning up I-75 around Vadosta, it was 102 on temp gauge. Tranny was running 205-209. I order for me to stay under 200 I had to slow down from 62 to 59. I stayed in overdrive. My normal towing rpm is 1950 with the 4:10's in OD.

Don't think you need another tranny pan. Just have 4 more qts of hot oil, if it gets hot. I don't know where you tranny temp is taken from, but like I said compared to mine its really cool. Could be just the difference in the two trannys and the way its set up. It could be reading from the Pan after the cooler.

I have a friend that had a 06 Mega Cab that traded for a 2008 Dodge 4500 with an Aisin Transmission in it. When he puts his rig in Tow/Haul it stays in 5th gear. His truck is running 4:44 gears. He also has a 6 speed tranny. It runs
2200 rpm's in 5th gear at 61 mph. It's a 6.7 Cummins like yours. That would be 1800 rpms in 6th gear which is were he runs it until he gets in the Hills.

My chart shows 1900 rpm at 59 mph in 5th gear, for your truck with 3.73's with stock size tires on it.

Forgot to mention 210-215 towing in the hills is normal with the outside temp
as high as you said.

Here is a tread you might want to read that has to do with mpg from the 4th Gen guys;

https://www.dieseltruckresource.com/...s-t295358.html

Dave

 

Thanks for the info Dave been a lot of help.

Our next trip out will be from FL to the Unadilla MX track in NY then off to
Steel city MX track. and that will be in late Aug.

I will keep you updated on how we do.

 

If your truck still has the complete emissions system on it, those numbers sound about right. I'm deleted and with my insight I can watch the engine load. Towing our TT on the flat stretches at 62 mph, in 6th, my engine is at 40-50% load and get 10.5 to 12 mpg. On the same road, same conditions, when I drop it back to 5th gear, I'm running just over 2,000 rpm, but my engine load drops down to 25-30% and my mileage pops up to 13.5-14.7 (all hand calculated). There was a little more drone at those rpm's, but I had a 5" chrome exhaust tip (that the previous owner put on) and once I removed it, the drone almost completely went away (plus I'm not a chrome exhaust tip kinda guy).

 

Great reply!

 

What is tow mode? and how do I tell what axle ratio I have.

2010 6.7 LB SRW get between 10.5 and 11.5 with a 4200# (pretty close to the loaded weight with me and the wife, fuel water and 10 foot single slide camper). 11400# gross. Got 12.5 mpg camper, me and no gear, dead level Tacoma to Portland 62 to 65.

 

Tow mode as used in my reply is related to Juice/Attitude device I installed in my truck. Look at the chart I posted that is for 3:73 rear. Compare the Rpm's
To speed for 6th gear. I'm working off my phone, so I don't have my spread sheets available for use. Extend the mph figures to the right as they are all pushed to the left.

Dave