I've got a Jayco 27 BH (Bunk House)... Pretty common TT ~6,000lbs loaded & 30ft long.

My previous truck an '06 Tundra w/4.7L V8 averaged a steady 8mpg towing this setup (once got 6mpg with HEAVY head winds). I bought this '05 2500 Cummins because it was cheaper than the Tundra and everyone I knew said it would tow the camper with ease and get ~12mpg.

Well I must be doing something wrong... because only one of those statements came true. The truck does pull awesome no complaints there. On my Tundra overdrive was useless so I had to pull in 4th gear (5-speed tranny) ALL the time flat, downhill...ect. And any good size hill (hill not hwy grade, but East/Central Texas hills) meant a reduction in speed by 5-10mph or a downshift to 3rd on the Tundra.

However, during our 4th of July camping trip last week the truck only netted 9.5mpg per the over-head computer. And before everyone says they are not accurate... I've noticed mine OH seems to be off by only 2mpg per each fill up, each time. So, that being the case this means the truck will only have gotten 7.5mpg when I fill up and verify by hand calculations.

It was hot this 4th... OH said 100-102 at hwy speeds. I tow around 65mph depending on traffic, and admit 70mph seems to keep the rpm's up for more power. I don't go over 70mph though,... I'd say 68mph is average for me for a nice straight road.

I tired towing with TH on & off... didn't see much difference between the two options both don't seem to shift into Overdrive until ~2,500rpm's or ~68mph (unless not accelerating much at all like in small towns). My technique was to go ahead and get to 70mph so it would shift into overdrive then slow down to 65mph if needed. Once in overdrive it pretty much stayed there (which was nice) and in rolling hills I coast down at 65mph the start accelerating a little bit before the bottom so the engine could start to build boost... then I just let the boost carry me up the hill.

Any suggestions? I keep hearing reports from other people who tow 5er's much heavier than mine and get low double digit mpg #'s. What should I change? I'm the kind of guy that likes mods... but I don't like impractical mods that reduce reliability or end up breaking things. If something has a small net gain but cost a lot I'd rather buy diesel with the money instead. I only average about ~10,000 miles a year 70-75% of that is towing our camper.

Thanks

 

I pull the camper in my sig, and last weekend I saw about 10mpg. I don't have any mods to the engine or tranny, just the lift and tires. I've tried the tow/haul mode and it does good for going down hills, but I find myself using the O/D off because it seems to keep me in the power (2-2500 rpms) a lot more. I think the lift and tires with the 3:73's messes keeps my rpms too low to use the Tow/Haul effectivley - unless I'm not doing it right.

 

One of the issues is , with the newer trucks [ not sure when they started ] they had 2 differential ratio's , 3:73 & 4:10 .
I never thought that was good unless you were towing very heavy loads [ near max , 18,000 lbs + ] .
With the older trucks , the chose was 3:54 & 4:10 , the 3:54 giving better millage , then tuning up truck for more HP's , to lug the heavier loads .
I your question you should give some MPH & RPM , numbers , go get some idea of what you have or not , fill in the signature with more detail , stock , moded , tires ect.

 

The OH computers are off by a percentage generally not a straight 2mpg... So 2 mpg at 20mpg is only 10%, meaning your off by 1 at 10mpg... But go off hand-calc only.

The truck has 208K miles on it.. what shape is the tranny in? Fuel/Air filters? Injectors?

6Klbs seems low for a 30' TT.... unless its a featherlite.

 

4.10 rear end, 6 speed stick towing 16,000 pound fiver 36' long. Run 60 to 65 if traffic allows. Consistently get 12.7 (within .2 either way) on trips to Alaska, Newfoundland, Mexico and all points in between. That is calculated by hand to verify and computer which is always within .2 either way at the end of a trip.

I seldom use the cruise except on very level roads. The cruise is very aggresive and really hammers the juice to try and maintain speed. I have tested the overhead on 25 mile stretches both ways and find the foot does a better job if there are many overpasses or hills around. It will also jamb it hard going up a hill when maybe letting it slow down a bit would be better. After comparing with a friend with auto running with me with a lighter rig, the cruise will cause the auto to downshift many times when it doesn't need to. I do find going anything over 60 costs me in mileage. Very high frontage on that fiver and speed kills mileage, even running solo.

Bob

 

1950rpm @ 70mph per my ScanGauge II, so pretty sure I have 3:73

Fuel filter changed by me ~500miles ago

Air filter looked clean but I blew it out anyway same time I did fuel filter

Adjusted valve lash 2-3 weeks ago by me to .10 intake .20 exhaust

Transmission was serviced ~4 weeks ago, had part (or half) of the valve body replaced because the truck was extremely hard to shift out of Park (issue was in some part of the valve body only ~a $100 part) Shifts were/are fine (a little tight), torque converter locks up like it should.

Truck is in great shape for 209K... Gets 19mpg empty easily.

Maybe I should try 60mph towing instead of my norm of 68mph? However, it seems the rpm's drop a little to low for hills and such at that speed.... and 60mph is really hard to do.

I understand towing a TT or 5'er is much different than towing a 15K goose neck flatbed due to the wind resistance. Are there others out there that get good #'s towing RV's 65mph or up? Honest, really numbers.... Just trying to figure out if something is wrong with the truck. I might go ahead and fill it up just so I'll know what the hand calculated rear # is... but it's not going to be better than the 9.5mpg the OH says.

 

On trucks (any generation of them), speed and frontal area is the enemy. Try slowing down a bit. On mine, towing at 62 mph vs 69 in the wind gives me a 4 to 5 mpg difference.

 

No slide, aluminum siding, 27ft long box + 3.5ft of hitch&bumper... Sticker inside says 5,050lbs w/out fluids, & 7,500lbs GVWR. So, it's 6,000lbs easily loaded (I only put ~5 gallons in the fresh water tank, other tanks empty while towing).

 

Regarding the injectors... When I go to Wal-Mart I see two kinds of PS. White w/black bottle and another one called PS Kleen (silver bottle). Which one should I get and will a good dose help/hurt?

Bought the truck with 207K so I don't know the history, but when I changed the fuel filter it was black'ish in color and kind of slimy. Which PS kills the algae stuff, if that's what this was?

 

I also pull the R/V in my Sig. I average 10-11 MPG pulling this 14,000 pound R/V all over the U.S. Running empty I get 22 MPG. This truck runs great.

 

Yeah, I average about 12- 14 mpg pulling a 10K lbs fiver.

Auto tranny with a shift kit, Smarty JR, and an open exhaust with an Amsoil Nanofiber air filter.

Head wind will kill you.....I tow in T/H all the time and ue cruise wherever I can. It really isn't bad unless you are in the mountains. You need to get that run at the bottom to keep the tranny from shifting.

 

i never have figured out what a auto might be good fore. that aside change the cam to pdr and 50 hp nozzles from ddp, do both at the same time to save labor and get a smarty jr. they all work together to reduce the emissions effect on mileage and will get you into the double digits. leave the smarty on economy setting, the auto can not stand stock torque much less the upper two settings.

 

Get the silver bottle. Add about 16oz to a full tank of fuel and run her hard (preferably towing).

MikeyB

 

i just noticed something you adjusted the valves at .10 and .20 i can not remember the year model they changed to i believe .12 and .28 look on the plate to see what you need i know my 06's are the new one because i did the same thing when i changed cam and ran it fore a week before catching it

 

Wow what's all that going to cost ball park wise? I have no idea, but I just quickly added up the "potential" cost savings of 8.5mpg vs. 12mpg. I came up with a cost savings of $425 a year in fuel cost. I'm hesitate to believe I can achieve 3.5mpg better with mods. Knowing my luck it will be much less than that.

How much mpg gain can I get from just a Smarty Jr. (real world, no marketing)? Is there any mpg gain in losing my cat and/or muffler?

I've got a 1000 mile camping trip coming up at the end of the month. Maybe I should wait until after that trip to see what the mpg numbers are on longer trips, before I dump money into it.