MPG @ 55 to 60 MPH

[quarrles]

Lots of good information here about diesel mileage. My experience, 2004 GMC 3500DRW Duramax and Allison tranny is to keep my RPMs at or below 2000rpm, approximately 64-65 MPH with 2008 Montana Big Sky 3400RLQ in tow. Mileage is consistent excluding hilly terrain @ 14.2mpg on onboard computer and 13.8mpg by fill and calculate method. I can not really compare to other folks calculations except to say that we all drive differently and that all conditions will be different.
We have ordered 2008 GMC 3500 DRW Duramax primarily for the new Allison tranny and to match our TV with F/W age. Will install a PullRite 18K super slider in new TV versus 16K Reese on current Tv.

[dsprik]

If I run 67-68, will I get better mpg with my 2002 D/A than I will at 62-63? My near 55 mph speed really downshifts Allison a bunch. Keeping my mph at 67-68 may be cause for a lot less downshifting/higher rpms than at 62-63. I guess it would depend whether your route was flat or hilly, though.

I also think that running in cruise control in hilly areas - something I do - also uses more fuel than driving with it off. What are your thoughts on this?

[richfaa]

I just ran over to the fairgrounds in Goshen pulling the 3400 anchor for the first time with my shinny new Ford 6.4L diesel. I am not impressed. Pulled the same camper over the same roads at the same speeds with the 05 V-10. The V-10 kicked butt..MPG 6.4L 8.2mpg.

[Hemlockusa]

Your not near broke in RIch, but what mileage did you get with the 6.4.????? Remember your hauling a BLENDER.... And also Rich, YOu will get a lot better mileage going to BRANSON from you location. It's all down hill. I will be looking for you and Helen there in MAY 2008. I have to give you that $10.00 to help out.. Me I can't afford that 8 cylinder, When I buy, I will have to go with the 6 cylinder. That's for us poor folk's.... Ha ha

[sreigle]

I have no idea what mileage the 6.4 will get when broken in. But I do know that stretch you drove is basically flat. I think when you get into some serious hills and mountains you'll see the difference in towing. Also, all of my diesels (gassers, too) have done more downshifting on slight hills until broken in. With the diesel you're probably looking at being past that point at about 10k miles. And it will get better from there. If like the 6.0 it should peak at around 30k-33k miles.

[Eagle Man]

It needs more miles on it.

[padredw]

Note to dsprick:

With two pickups, first one gasoline--second diesel, I never used cruise control. Holding a constant speed will IMO certainly use more fuel. I let up on the uphill (except mountain passes) and allow to speed up a bit downhill.

Also, in contrast to many other members of the forum, I use the tow/haul only in the mountains. I get good "shifting" in drive otherwise and tow in overdrive on level.

Not to tell anyone else what they should do; just my own opinion and practice.

[sreigle]

Dave, I used to use cruise all the time. Now I kick it off when doing hills and allow the truck to slow a bit going up and gain some speed back going downhill, all in the interest of fuel economy.

My foot must not be as steady as Padre's because on relatively flat land the cruise gets better mileage than I can without cruise.

I use the tow/haul all the time, with few exceptions, because I have seen on the gauge how the transmission runs cooler in tow/haul. That may not be true on all vehicles but it was on my Fords. I don't yet have a transmission temperature gauge on this Dodge so am running tow/haul just to be safe. I turn the tow/haul off in town on the Dodge because with the exhaust brake on AND the tow/haul on, low speed downshifts in town can be a bit jerky/sudden. Not harsh, just a sudden deceleration that bothers my passenger.

What works for me on my trucks may not work for you.

[Eagle Man]

quote:Originally posted by padredw

Note to dsprick:

With two pickups, first one gasoline--second diesel, I never used cruise control. Holding a constant speed will IMO certainly use more fuel. I let up on the uphill (except mountain passes) and allow to speed up a bit downhill.

Also, in contrast to many other members of the forum, I use the tow/haul only in the mountains. I get good "shifting" in drive otherwise and tow in overdrive on level.

Not to tell anyone else what they should do; just my own opinion and practice.

The GM manual says to use T/H if the GCW is equal to or greater than 75% of the GCWR. Has something to do with the Allison working the way it's supposed to work when pulling heavy loads.

[dsprik]

I just started this practice - after pulling for over a year full time with cruise. Coming to the rally today, I only used cruise on the flat areas. When I saw a hill that potentially was going to cause a downshift, I kicked off my cruise and feathered off of my gas so as to not let it downshift. I also went to the trucker trick of letting myself gain speed going down a hill just prior to another one. This has got to be better than full time cruise and letting it smack the 3000 rpm level like it was doing...

I need to get out of the habit of thinking of myself as a 4 wheeler when towing, and start thinking of myself as a driver with a load...

[Allen in MT]

I've got a dodge 3500 6 speed and find that when I stay under 2300rpm that is where I get the best milage, anything above 2300rpm and it goes down. I tow the mt 3400rl and it drops about 10 mpg. has anyone got the bully dog chip in their dodge and does it help with power, milage or both
Allen in MT

[Ozzie]

Regarding the use of cruise control and hills...my previous TV was a gasser (didn't buy it for towing an RV), that poor thing just died on the hills. I had to get a 'run' at the hills to keep it from screaming in the lower gears to make it.
I've done some remodeling work for more than one highway patrol and asked them if they pay attention to someone taking a run at a hill when towing an RV. The response from both of them was as long as they don't maintain the higher speeds they don't bother.

Now that I have a diesel, even though it has the power in the hills, I feel it is a good practice to still take a run at the hills to keep it from downshifting. You can still do this with cruise if you want, just feather it a little in advance of the hill and you're good to go.
I have found that mileage drops pretty hard with cruise on if you just let it have it's way.
Sometimes it's worth it to just relax and not worry...everything has it's price.

[dsprik]

Bruce, you make a ton of sense... Thanks for the info on the Highway Patrol...

[Montana Sky]

quote:Originally posted by dsprik

If I run 67-68, will I get better mpg with my 2002 D/A than I will at 62-63? My near 55 mph speed really downshifts Allison a bunch. Keeping my mph at 67-68 may be cause for a lot less downshifting/higher rpms than at 62-63. I guess it would depend whether your route was flat or hilly, though.

I also think that running in cruise control in hilly areas - something I do - also uses more fuel than driving with it off. What are your thoughts on this?

Dave,
My truck also gets its peak fuel economy towing between 67-69 mph which puts me right at 1,900 rpm's. On the flats and rolling hills I will roll along right at 68 mph. The tranny will hold 5th gear on the rolling hills unless I start out slower, than it will down shift into 4th. Once into the mountains I turn the cruise off and just use my gut feeling to tackle the speed on the climb up and decent down.

[dsprik]

Thanks, Dave! I believe I have been wasting a little too much fuel this past year relying on my cruise control too much. Oh well... it's only money... I will change my driving habits. At $81 a bbl, I may start turning the truck off going down hills. Probably a bad idea...

[Montana Sky]

Dave,
Try a few tanks rolling along just shy of 2,000 rpm's -- as long as your comfortable towing at 68 mph. I do use the cruise on the flats, but more often I find myself not using it.