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Is the bad fuel mileage?

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We were finally able to get out and take a trip last week. Went from Colorado Springs to Custer, SD for a few days. This was our first trip with the truck and I loved it except for the fuel consumption.

2011 Volvo 730, D 13 set at 435 HP, 3.55 gears, I shift with 707k miles.

I was towing 19k. and the truck weighed in by itself at 21k so total package was 40k. That’s pretty good with the cipherin’ right there! We like the road less traveled when we can and avoid Denver at all costs so we went east and then north through eastern Colorado and western Nebraska so we had plenty of wind.   

I don’t have exact mileage vs fuel used. We left with two full tanks so 250 gal. of fuel and went 950 miles total. My fuel gauge is showing 3/8 tank left. I don’t want to fill it up for an exact amount of fuel because if I have contaminated fuel or something it would be less of a mess to deal with. Not sure that is the issue but…

The dash shows I averaged 3.4 mpg on the trip and that is what it shows bobtails as well. I’m sure that thing isn’t the most accurate tool to go by. If the fuel gauge is accurate, the math says I use about 150 gal so the mileage would be around 6.33. That’s still half of what I got bobtailing it back from Seattle.

I’m trying not to overlook the easy stuff so first I checked the air filter and I have a new one I could install but it looks clean.

The fuel filter also looks OK, might need to swap it out, don’t know if that would be enough to cause a 50% reduction.

Couldn’t find any signs of a fuel leak.

Might be time for injectors but wouldn’t that go bad over time?       

Am I missing something?

Andy

 

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Ignore the lie-O-meter.  The only way you'll get accurate fuel mileage is by actual fuel consumed.  So unless you can accurately determine fuel levels in your tanks, you're only guessing at this point and at worst, getting anxious over a problem that may not even exist.

Dip your tanks and determine if there's water and/or sediment.  Replace your primary fuel filter.  Depending upon what type of filter you have, you can cut open the old one and see what might be trapped in the pleats.  If these don't suggest contaminated fuel, manually calculate fuel useage.

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D12 with 3:73  12 speed freedomline,for the last 7 years I have got from low 8 's to a little over 9.

Wind is a factor and your ground speed, one of the best runs ever was coming back from Fl this spring , Even thought I way exceeded my usual speed a flag stiffening tail wind had my avg at 9.2.

that was a full tank(s) from Macon to Detroit,got home with a 1/4 left.

 

I use the lie o metre because i checked it and its close enough for my use

Edited by hone eagle

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I hope your 3.4 mpg dash display is wrong.  My display is usually within .1-.2 mpg of what my calculated number is.

Our 2006 VNL 780 D12 465 hp with 2.86(?) gears, 579k miles, and a loaded towing weight of around 41k lbs gets between 6.3 and 7.5 mpg  loaded when towing at 60 mph depending on wind and terrain and stops/starts.  But I have seen as low as 5.3 mpg while towing and traversing steep roads.  Bobtailing at 55-60 mph usually gets us 9.0-10.5 mpg....again depending on the conditions.  Bobtailing with a strong tailwind on relatively flat land has put us over 11 mpg a couple of times.

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44 minutes ago, Parrformance said:

Have you spotted any black smoke out if the stack?

Does it look as though the turbo is original?

No smoke at all and it does look like the original turbo. I took it to our local Mack shop because they're the only shop in town that will work on a Volvo. The mechanic that looked at it said new injectors but his boss heard that and checked in to it and said he didn't think injectors.   

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What speed and engine RPM were you traveling at?    There is a sweet spot for each truck, also how much back of the cab to trailer?      Are the tires aired up?     Do you have a brake dragging?     There are a lot of little things that skew mileage.

 

Steve 

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1 hour ago, Steve from SoCal said:

What speed and engine RPM were you traveling at?    There is a sweet spot for each truck, also how much back of the cab to trailer?      Are the tires aired up?     Do you have a brake dragging?     There are a lot of little things that skew mileage.

 

Steve 

All good questions and more info I should have shared. 65 most of the way at 1400 rpm. Tires are new and aired up. I have a monitor and didn’t notice any excessive tire temps so I don’t think I have a break dragging but I’ll check that for sure.   The bed is 10’ from dorm to hitch but it shows the same mileage bobtail. 
 

thanks for the help

 

andy. 

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What speed were you running?  Most of these trucks were set up- HP, TQ, rear end gears, transmission, and tire size to have an optimum mileage at 65mph.  So running 70 will hurt the economy.  And as stated above, what was the wind like?  Hill country with climbs?  Tire pressure?  Distance to the trailer?- 

Distance to the trailer- Roger Jones and I had identical Volvo 610's.  Same engine, transmission, rear end, tire size.  He went with a long deck, while I went with a truck that had been singled short.  Pulling similar weights, I usually get 10.5mpg while he averaged 8.5 to 9.

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3 hours ago, spindrift said:

Ignore the lie-O-meter.  The only way you'll get accurate fuel mileage is by actual fuel consumed.  So unless you can accurately determine fuel levels in your tanks, you're only guessing at this point and at worst, getting anxious over a problem that may not even exist.

Dip your tanks and determine if there's water and/or sediment.  Replace your primary fuel filter.  Depending upon what type of filter you have, you can cut open the old one and see what might be trapped in the pleats.  If these don't suggest contaminated fuel, manually calculate fuel useage.

I dipped the tanks tonight and it looks like the gauge should be accurate. No sign of water or sediment. The fuel filter looks dirty to me so I’ll swap it out tomorrow night and go fill it up to get more accurate numbers. 
 

you might be right in the money about making something out of nothing, plenty of other things around here to work on without creating something. 
 

thanks for the new term, lie-o-meter, is new to me  

Andy

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Gotta hand calculate over several fill-ups.  Going from CA to S. Carolina we got between 7.5 and 8MPG.  60-65MPH, 1400-1450RPM, towing a 27K 5th wheel.  DD15.  Lots of variables.  Rear end ratio is also huge.  Wind is also a factor.  Going E, with my dodge and a lighter 5th wheel, we got 9MPG with constant headwind.  Go West on return, with strong tailwinds, we got over 11MPG!  Here is a quote from facebook by Greg Shields who used to customize OTR truck for towing HDTs: "

I have had the unique opportunity to use many RV Haulers with D12s, D13s, and D16s. I have also towed with horsepower ratings of 435, 450, 485, 500, 535 and up to 600 HP! Please note that I drove the same roads for hours and days at a time, with the same loads of Smart cars, tools, and the same trailers (5th wheels) between these various RVHauler powertrain combinations. Certainly, this is only my opinion, and other folks have other experiences.
Engine size / HP is not a top factor in fuel economy in my side by side comparisons or in my uses over the years.
#1 Speed that you drive
#2 Wind (headwind, sidewind, tailwind)
#3 Hills / Grades
#4 Rear End ratio
#5 Engine size
#6 Engine mechanical condition (injectors etc)
#7 Fuel grade and quality
The next variables are somewhat lumped together, and I find it hard to say which have more impacts than others...
I shift transmission Vs ZF Meritor and other autoshifts
Trailer and load weight
Tire inflation and fuel efficiency
How often and how hard you put your foot down on the throttle
I can take any of the above variables, and make it overwhelm all the other variables - and get awful mileage.
If we made all the other variables identical between RVHaulers and just play with the engine size, transmission, rear end ratio and HP - here are my thoughts...
We try to get a reasonable combination of the variables above - and we do ok - 11 MPG. If we have one really really out of spec or a less-than-perfect combination of variables - we are in the 7 MPG range. It seems we can be in the 7's quite often. I personally have spent hundreds and hundreds of hours enjoying my RVHaulers and traveling to (almost) every corner of US / Canada. I am no longer entirely focused on fuel - I now tend to care about safety, comfort, longevity, performance, and lastly fuel economy - that is just me.
My favorite combination - D16 at 500 hp, ishift, and a 2.67 rear end ratio. I LOVE the horse power and torque - this is my preference, and again every driver will have their own likes and dislikes. I LOVE driving up the steepest 10 mile grades at 75 MPH, and passing every LGT (Little Girly Truck). Ok, and the rear end ratio is fantastic - cause it just hums along at 1100 RPMS at 65 MPH. 10-11 MPG with this combo but I do the majority of my driving (80%) in the rocky mountains - crummy fuel economy conditions. Yup, the performance matters to me, and I will compromise the fuel efficiency for the ability to accelerate, climb hills and pass. Hey, I have worked my whole career, and I have given myself permission to have something that "turns my crank".
AN ASIDE - (Manly man moment) The biggest thrill towing was courtesy of the RVHauler named PRINCE that I had the honor to use for 1.5 years - the Volvo 880 with 600 HP. That engine would actually twist the frame a bit on hard acceleration. AWESOME.
The best fuel economy is going to come from D13 in and around 435-485 HP, i shift or ultrashift, and driving around 65 MPH. (not doing 75 MPH passing everyone going up-hill). Closer to 11 MPG average is feasible.
Ratios to stay away from 3.55 3.73 - nope, no way. They are going to push your fuel economy lower.
I have some YouTube videos where I did side by side comparisons - same engine, same weight, same driver, same speed, same accelerations, etc, and ONLY changed the rear end ratio - the result - 1.5 MPG difference saved when you go to a 2.67 vs a 3.53. As you can see - change one variable and you can see a significant difference. I hope that helps."
 

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I have to agree with "most" of what Brad said,

 

My truck has a C13 1650/500 and .74 OD with 3.70's      The OP has 3.55's with an I-shift is that .82 or .74 in high gear?     Final drive gearing is the real number, my 3.73's with .74 OD have an effective 2.738 ratio not much different than a straight through trans with 2.67 gearing.

My truck and Kentucky trailer are about 45K and I drive at 70-75 where able, I see 7.5- 9 MPG, the trailer is 28" from the back of the cab

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If you have the standard cylindrical tanks you can go to https://halltank.com/tank-charts/ and input your dimensions.  It will then give you a list of inches to gallons.  So if you dip your tanks, measure the depth, then use the list you will know how many gallons of fuel remain.  For my use it has been very accurate.  If you do this you can find your fuel usage without filling up.  Hope this helps.

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7 hours ago, Steve from SoCal said:

the trailer is 28" from the back of the cab

I believe that's what hurts mileage for many of us.  We have roughly 13' from BOC to front of trailer.  We're pushing air twice.

Over the years, we've averaged 7.2 mpg.  Head winds have pushed it as low as 5.5, and tail winds have netted around 9. Dash readout on ours is very optimistic.

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Do you know the DEF ratio from the previous trip?  Was the DEF tank full when you left?   Maybe refill the DEF tank and divide by 4% (or your actual ratio) to get a rough idea of fuel burned without refilling fuel?

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My dash meter tends to be slightly pessimistic. Two weeks ago ran west across 94/90 to Bozeman, 6.1 mpg pulling a paltry 6500lb TT. There was a really good headwind most of the way, and I was making pretty good time.

Return trip across Wy and SD did’t have a lot of head wind but plenty of cross wind. Got up to 6.5 by the time we got home. Didn’t go any faster than 77 as that’s all she’ll do.

I don’t care to hand figure mileage, it’s not that important. We had a great time, that is what’s important.

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2 hours ago, Moresmoke said:

 

Return trip across Wy and SD did’t have a lot of head wind but plenty of cross wind. Got up to 6.5 by the time we got home. Didn’t go any faster than 77 as that’s all she’ll do.

 

It's hell not being able to speed in Montana.....  We can barely get there if there is no wind.  We either need another gear or a better rear gear....  

 

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The longer I have my truck, the more the fuel mileage decreases. When I first purchased I was getting over 9 on the computer read out. Of course it was "Bob Tail" for almost 8 months before finally hooking up to my first trailer. Seemed to stay the same for a while and then I started to change the truck and finally the trailer. I'm a lot more heavy, have removed the side fairings(Wish I hadn't), have a taller box (Drom) and of course a much heavier trailer. I no longer keep the display on the MPG setting and instead it's on the clock and sometimes my "average speed". I fill up when I need or want to and am happy my truck is providing me with a driving experience many others can only dream about. "Priceless". 

 

Rod

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On 6/22/2020 at 9:56 PM, Steve from SoCal said:

I have to agree with "most" of what Brad said,

 

My truck has a C13 1650/500 and .74 OD with 3.70's      The OP has 3.55's with an I-shift is that .82 or .74 in high gear?     Final drive gearing is the real number, my 3.73's with .74 OD have an effective 2.738 ratio not much different than a straight through trans with 2.67 gearing.

My truck and Kentucky trailer are about 45K and I drive at 70-75 where able, I see 7.5- 9 MPG, the trailer is 28" from the back of the cab

Howdy Steve,

Your trailer being “28” from our back of the cab”, doesn’t that greatly affect your ability to maneuver in tight places?

As most of our trailers are 102 wide we need to have a a bare minimum 51” between the trailer and the back of the cab in order to get the trailer 90 degrees to the back of the cab.  51” gives NO margin for error of any kind.

Real world number to allow for uneven ground or flex of any source or kind puts the distance needed from the trailer to the back of cab to anywhere from 53” to 56” depending on one’s personal preference for not causing any damage when maneuvering into or out of tight situations.

 I would appreciate knowing if the 28” distance from back of the cab to the trailer has caused you any maneuvering problems, thanks for any information you can share.

Dave

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59 minutes ago, mr. cob said:

Howdy Steve,

Your trailer being “28” from our back of the cab”, doesn’t that greatly affect your ability to maneuver in tight places?

As most of our trailers are 102 wide we need to have a a bare minimum 51” between the trailer and the back of the cab in order to get the trailer 90 degrees to the back of the cab.  51” gives NO margin for error of any kind.

Real world number to allow for uneven ground or flex of any source or kind puts the distance needed from the trailer to the back of cab to anywhere from 53” to 56” depending on one’s personal preference for not causing any damage when maneuvering into or out of tight situations.

 I would appreciate knowing if the 28” distance from back of the cab to the trailer has caused you any maneuvering problems, thanks for any information you can share.

Dave

Hello Dave,

 

The trailer is a 48' Kentucky semi trailer with a 36" king pin setting.     My Teton trailer is 62" to BOC.     RV 5th wheel trailers have little or negative king pin setting for use with pick up trucks.     Where an RV need the distance of the hitch to the outer body for clearance, a semi trailer with a deep pin setting includes the pin depth in that figure.     The 36" pin has my Kentucky trailer positioned where 3 feet of the trailer swing clearance is baked in.      With the front corners beveled the swing clearance on my semi trailer is 58"      Doing the math 58-36 is 22, add 6" and there is the 28" trailer to BOC.   

 

When I was building my truck I knew that to keep the overall length to 65' I would have to be very close coupled, I am at 65' +2.5" for the dot bar at the back of the trailer, I may rework that if it becomes an issue.     The 6" allows about 8-9 degrees of dip and the bed acts as a limiter, the bed prevents the trailer from dipping more than 7 degrees.     I used the approaches to my shop to confirm there was enough margin for going up drive ways,  the approach to my shop is 30" of rise in 12 feet.   I devoted the time and engineering to get what I have, I chose this exact truck model for this reason.    The short nose allows me to hit the 65' number, a long nose 387 would have been 8" too long.     I could have used a truck with a smaller sleeper to get that number but, it would have been much more difficult to conform to the RV requirements.

 

Steve    

20200319-150436.jpgimage share upload

Edited by Steve from SoCal

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On 6/24/2020 at 10:46 AM, Steve from SoCal said:

Hello Dave,

 

The trailer is a 48' Kentucky semi trailer with a 36" king pin setting.     My Teton trailer is 62" to BOC.     RV 5th wheel trailers have little or negative king pin setting for use with pick up trucks.     Where an RV need the distance of the hitch to the outer body for clearance, a semi trailer with a deep pin setting includes the pin depth in that figure.     The 36" pin has my Kentucky trailer positioned where 3 feet of the trailer swing clearance is baked in.      With the front corners beveled the swing clearance on my semi trailer is 58"      Doing the math 58-36 is 22, add 6" and there is the 28" trailer to BOC.   

 

When I was building my truck I knew that to keep the overall length to 65' I would have to be very close coupled, I am at 65' +2.5" for the dot bar at the back of the trailer, I may rework that if it becomes an issue.     The 6" allows about 8-9 degrees of dip and the bed acts as a limiter, the bed prevents the trailer from dipping more than 7 degrees.     I used the approaches to my shop to confirm there was enough margin for going up drive ways,  the approach to my shop is 30" of rise in 12 feet.   I devoted the time and engineering to get what I have, I chose this exact truck model for this reason.    The short nose allows me to hit the 65' number, a long nose 387 would have been 8" too long.     I could have used a truck with a smaller sleeper to get that number but, it would have been much more difficult to conform to the RV requirements.

 

Steve    

20200319-150436.jpgimage share upload

Howdy Steve 

Thanks for your reply and information it all makes sense now I thought you were dragging the typical RV trailer 

Dave

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Work has been getting in the way and I haven’t had time to jump on here and thank everyone for the all the input. Great information, as usual!

 The fuel filter was dirty so I changed it out and went ahead and swapped out the air filter as well. Clean fuel and air, makes for a happier engine. Who would have guessed?

I also believe I didn’t start out with as much fuel as I thought. Took Blueflame’s advise and dipped the tanks. Right was at 14” and the left was at 9”. Don’t know if that’s normal or not and I won’t put any thought to it because the left side cap was just sitting there and I know for a fact it was tight so I suspect someone got some discounted fuel one night. We’ve had some of the nonsense going on in the area.

Best advise of all, fill the tanks and enjoy the ride. Sure was nice not being pushed around by the trailer!

Thanks again all for putting up with the newbie questions.

Andy

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