First major tow with new Jayco 31BHS TT - 8 mpg for 4 tanks - Diesel Forum

David C · 05-09-2006, 12:28 AM

Pulled down to Mississippi to do Katrina repair for a week. Four volunteer carpenters in truck, about 1200 pounds of tools in bed, and the trailer. Truck had averaged 16.5 mpg for 89000 miles previously, but mileage was cut in half when towing. Four tanks emptied calculated to almost the same mpg. The fifth tank added has not yet been fully consumed.

Despite lower than expected mpg, the rig towed great. The Equal-i-zer brand hitch had been setup by dealer with truck and trailer empty, using 1200 pound bars. We had a level running non-sway tow. I believe I can fine-tune the hitch setup a little to better accomodate loading, but did not have time before the trip. When trailer was dropped on ball of loaded truck, the rear of truck dropped two inches. Installing the bars raised the rear about 1/2 inch.

I drove right at 70 mph when possible, and my other experienced driver usually ran 75+. Almost all miles were on interstates. Next trip will be less demanding on time, and I will try staying 65 or less mph to see what happens to the mileage numbers. The truck did hold gear better on long rises when running at the faster speeds, but traffic and speed limits do not always allow that.

I am pleased with the ride and the trailer model, but of course would like to improve mpg. Also running a new set of BFG 285/75/16 AT/ko E rated tires. They were smooth and quiet on the trip.

Sample · 05-09-2006, 01:15 AM

I know if I drive above 70mph my truck sucks the fuel.

allenp412 · 05-09-2006, 08:37 AM

I get about 12mpg pulling at 65mph (alligator alley)
When I run 75-80 I get about 8mpg.
25ft TT at about 9k

Allen

SmokeyWren · 05-09-2006, 11:04 AM

Speed makes a big difference. Because you're pulling a big barn door into the wind, the aerodynamic forces kill your MPH at higher speeds. Here's my experience towing a mid-profile 5er with a GCW of about 16,000 pounds with stock-size tires and a calibrated speedo across relatively-flat terrain on the plains:

73 MPH = 8 MPG @2,150 RPM
70 MPH = 9 MPG @ 2,000 RPM
67 MPH = 10 MPG @ 1,900 RPM
63 MPH = 11 MPG @ 1,800 RPM
60 MPH = 12 MPG @ 1,700 RPM, but downshifts too much.
58 MPH = 1600 RPM but downshifts to direct drive for every little bump in the road so I don't go there.

For my hot-rod towing machine, 1,800 RPM seems to be the sweet spot - decent mileage without the irritation of the tranny downshifting often. But with a stock engine, I had to cruise at 1,900 RPM to eliminate the constant downshifting.

So for yours, I'll bet slowing down to 63 MPH will get you about 10 to 11 MPG - provided your speedo is calibrated to 636 tire revs/mile so your odo/tripmeter is accurate - and provided your engine produces enough HP at that speed to not downshift for every little bump in the road.

For a stock engine with 285 tires, you may have to run 1,900 RPM to make enough horses. In that case you're looking at 68 or 69 MPH as your minimum comfortable speed, so 8 to 9 MPG may be all you an expect.

Plus stiff headwinds can knock off one or two MPG, and strong tailwinds can add one or two MPG. Hills and mountains also affect MPG. [img]/ubbthreads/images/graemlins/smokin.gif[/img]

ZR1PETE · 05-09-2006, 11:22 AM

My King Ranch CC dually running at exactly 64mph pulling a 12000 LB Cedar Creek manages 13.5 mph hand caculated. Me very much happy [img]/ubbthreads/images/graemlins/cool.gif[/img]
But then again, I not in any hurry.

David C · 05-09-2006, 01:18 PM

Appreciate the comments and detailed mpg data. Yeah, we were running faster than I really wanted due to time constraints. Next trip is family only so not under pressure to roll.

Also I did not mention I was using a Diablo chip on way south. On starting the generally uphill return trip (sealevel to about 1000 feet) I noticed the EGT was running too hot so pulled chip to lower temp. Could not see any difference in mpg, but had more frequent downshifts.

Wildman_78 · 05-09-2006, 03:53 PM

Do you guys notice any difrence with a small chip VS stock in over all MPG? I was considering a small chip to kinda take the 'hurt' out of some of the bigger hills. Am I thinking along thr right lines? I have already done the exhust, and noticed a defenite difrence.

SmokeyWren · 05-09-2006, 04:46 PM

[ QUOTE ]
Do you guys notice any difrence with a small chip VS stock in over all MPG?

[/ QUOTE ]

Sure. Unloaded, with the chip installed, I got worse MPG. Not because the chip was was poorly programmed, but simply because it was so much more fun to mash on the go pedal - and I have no will power. [img]/ubbthreads/images/graemlins/blush.gif[/img]

But heavily loaded or towing, no significant difference.

If you have enough willpower to drive exactly the same way with the chip as you do without it, then you might gain a smidgen of MPG when unloaded - such as using the truck as a commuter car. But not enough to write home about.

Slide5th · 05-09-2006, 09:27 PM

I run a 65HP tow chip,run at 65MPH when safe to do so,and gross 21800,get around 10.5mpg,running up and down the east coast.If truck was stock i don't think i would get any better consider the weight of my rig.

David C · 05-10-2006, 12:54 AM

[ QUOTE ]
Do you guys notice any difrence with a small chip VS stock in over all MPG? I was considering a small chip to kinda take the 'hurt' out of some of the bigger hills.

[/ QUOTE ]

What Smokey said!
The chip makes the truck seem more peppy even when not pushed hard, and on long hills the trans does not shift down as soon or as often. But the EGT does run hotter and if you have not opened the exhaust you have to back off throttle to reduce temp. That can be counterproductive to the reason for having the chip. I have original exhaust in place.
My chip has been in place constantly for over four years. Probably better programs are available now that would improve the temp vs performance conflict.
I am going to leave the chip off for a few months (if I can stand it!) to see what happens to mpg longer term. When I added chip could not really tell any difference, and doubt if I see change now. But I plan some mountain runs soon and think the high EGTs would be more of a problem than running without the chip.

Sparkydm · 05-10-2006, 08:39 AM

"My King Ranch CC dually running at exactly 64mph pulling a 12000 LB "
That's in the range I get pulling my boat which scales at
12.5K. I usually travel between 62 - 65 mph. It will easily go over
70 mph and would actually pull hills better but, I prefer to have
the fuel economy and people slowly passing me. It gives an added
safety margin for the bright people that tend to get in front
of long heavy loads and decide to do a brake test. [img]/ubbthreads/images/graemlins/biggrin.gif[/img]

Allister73 · 05-10-2006, 10:20 AM

Guys, I would tend to agree with DavidC. I have a Wildman chip, and pulling hills I do see an increase in egts, over stock, but even when I back out of the throttle, I haven't an innercooler! I can still pull a steep grade much faster than stock. I have done hand calc economy stck and chip. Stock=16.34, Chip=18.63. I kept track carefully so when I got the chip I could compair. I see a small increase while towing, but most of the increase is in patience. I do not get upset when 98 year old Granny passes me on a small hill. With diesel at 2.99/gal here in Colorado Springs, I have my wife paddle going uphill to see if it helps. Colin [img]/ubbthreads/images/graemlins/tongue.gif[/img]