Quite dissapointed in mileage

[dobienut]

Took my truck and trailer (trailer rated for 14000kg) and drove 3.5 hours to pick up a backhoe attachment, drove back. Filled up and checked my mileage and was very dissapointed to see the result! 11.6 mpg

[LiveOak]

What speed do you typically drive at?

[flagmanruss]

Well, I took my camper on a few jaunts this year... I was pulling 10s. The trailer has all of the aerodymanics of a brick & it seems pretty darn heavy. I'm planning to take it by the truck stop scales in the Spring, in fact. But then I have 4:10 gears & my best mpgs running empty & babying it (40-50) is 18.7. I don't know your weight or windage... and winter fuel... I'd be disappointed too but not overly surprised.My old Chevy is gone now. C30, camper special, 454, built, towing cam, Edelbrock intake, 650 AFB, headers, 3:73s got 11. It didn't matter towing heavy or running empty, it got 11.

[dobienut]

What speed do you typically drive at?

Well I cruise along between 70 -75 mph which is truckin along, but seems wierd how I knowof guys towing 4 snowmobile enclosed trailers getting better mileage, and I can be sure they aren't slowpokin

[dually]

Winter fuel blend? It kills my mpg.

[LiveOak]

#2 diesel has an approximate 5% higher btu content than #1 diesel. If you are burning #1 diesel (I suspect you are that far north), you will see a slight drip in fuel mileage as compared to #2 diesel.

http://en.wikipedia.org/wiki/Fuel_efficiency

The big fuel mileage killer is the speed at which you are driving. The most efficient speed for these trucks is around 45 mph or about 72 kph.

In any particular object moving through the air (as a ground vehicle), there is a sweet spot in which the least amount of energy is required to move it the farthest. In this instance the types of drag that come into play are "parasitic drag" and "profile drag". These are both combined into "form drag". This comes into play MUCH more in aviation as you might expect and "induced drag" plays into the equation.

For the purposes of illustrating how drag comes into play more and more with increased speed, we are looking at "form drag" with motor vehicles. If you look at the chart, you can see where the induced and form drag lines intersect. This is the max efficient airspeed for an aircraft. Now, our trucks are not flying but note how the form drag line radically climbs with increased airspeed. As the airspeed is doubled, the form drag is SQUARED. That means LOTS of drag going fast.

http://en.wikipedia.org/wiki/Parasitic_drag

Summed up:

Power

The power required to overcome the aerodynamic drag is given by:

Note that the power needed to push an object through a fluid increases as the cube of the velocity. A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 80 hp (60 kW). With a doubling of speed the drag (force) quadruples per the formula. Exerting four times the force over a fixed distance produces four times as much work. At twice the speed the work (resulting in displacement over a fixed distance) is done twice as fast. Since power is the rate of doing work, four times the work done in half the time requires eight times the power.

http://en.wikipedia.org/wiki/Drag_(physics)

Fuel consumption changes radically with the above drag increase.

In another life, I had to compute this and other factors & requirements prior to take-off. By selecting the optimum altitude, airspeed, cabin heat, and engine anti-ice requirements as well as other factors, fuel consumption would vary between a minimum of around 700 lbs. per hour vs. using max. continuous power or 30 minute limit power which would increase fuel consumption to upwards of 1,200 lbs. per hour. Or about a 100 gallons per hour vs. 180 gallons per hour.

If I cruise at about 50 mph or 80 kph, I typically get about 22 to 24 mpg. If I increase this speed to 75 to 80 mph or 120 - 128 kph, my fuel mileage drops to around 11 to 13 mpg depending upon how much weight is on the truck. If I am towing, it drops even more.

Another issue in addition to the right foot that could effect fuel mileage is a dirty or inaccurate reading IAT sensor.

http://smokindiesel.com/Technical.htm

http://dodgeram.org/tech/dsl/sensors/IAT/clean.htm

Most diesels will get slightly lower fuel economy in cold weather due to more fuel being required to maintain environmental heat in the engine.

Be sure to check and verify no boost leaks in the turbo plumbing.

Mike has a great write-up on cleaning & inspecting both the IAT and MAP sensors:

http://mopar.mopar1973man.com/cummins/2ndgen24v/map-sensor/map-sensor.htm

Try all the above or what you think may apply in your case and see what if any improvements you can make in fuel mileage.

[Wild and Free]

Took my truck and trailer (trailer rated for 14000kg) and drove 3.5 hours to pick up a backhoe attachment, drove back. Filled up and checked my mileage and was very dissapointed to see the result! 11.6 mpg

What type of trailer Gooseneck or bumper pull? How long is the trailer? Like posted above was it #2 or winter blend fuel?

[Mopar1973Man]

Just going from 55 MPH to 65 MPH your wind drag will nearly double but going from 55 MPH to 75 MPH the wind drage will nearly be 4 times... Speed is not your friend... This is just a truck alone... Tyipcal drag co. is about .46 to .48 but now the graph doesn't include trailer of larger frontal area but you can imagine the curve gets more aggressive with a larger frontal profile and more speed.

[Wild and Free]

But what about going 75 with a 25 mph tail wind?

[white01]

But what about going 75 with a 25 mph tail wind?

better fuel mileage than a head wind!!!

[Mopar1973Man]

But what about going 75 with a 25 mph tail wind?

Technically it would be like just subtracting the 25 from the 75... So it would be the same as driving 50 MPH. Simple logic...

[Topahat]

Well you are getting air out with that exhaust but are you getting air into the motor. Plus grab up a chip to smooth out your fuel curve because the MAP sensor just spikes up and down continuously. If you are running a wide and tall tire narrow it down some (takes extra power to turn that rubber) and check tire pressure. Plus its notorious for a manual transmission to consume more fuel due to inconsistent shifting. I aint saying your a bad driver, just saying shift points are never the same.

[JOHNFAK]

Took my truck and trailer (trailer rated for 14000kg) and drove 3.5 hours to pick up a backhoe attachment, drove back. Filled up and checked my mileage and was very dissapointed to see the result! 11.6 mpg

Lost - what kinda of trailer - an empty one ??? But rated for 14000 ?? I have been all over this on 3 forums. A loaded RV/TT will get 10-14 mpg on a 24v. Generally 12-13. Anyone that said different pretty much didn;t sound like they knew what they were talking about. Obviously there is some variation if what your towing is not a RV/TT and doens;t weigh 7500-12000 lbs. Individual truck styles also vary - different gears , chips, injectors, transmissions, HP. Unless it was empty - 11.6 sounds ok to me.

[Wild and Free]

Technically it would be like just subtracting the 25 from the 75... So it would be the same as driving 50 MPH. Simple logic...

There have been times when I got better milage driving into a side wind rather than driving with a side wind.

[Blueox01]

Lost - what kinda of trailer - an empty one ??? But rated for 14000 ?? I have been all over this on 3 forums. A loaded RV/TT will get 10-14 mpg on a 24v. Generally 12-13. Anyone that said different pretty much didn;t sound like they knew what they were talking about. Obviously there is some variation if what your towing is not a RV/TT and doens;t weigh 7500-12000 lbs. Individual truck styles also vary - different gears , chips, injectors, transmissions, HP. Unless it was empty - 11.6 sounds ok to me.

It's an empty trailer Gooseneck Flatbed w/a GVWR of 14k ,Round trip 3.5 Hrs half empty/half loaded. Empty the Trailer is about 5k,he does'nt say how much the attachment wieghed.

[JOHNFAK]

It's an empty trailer Gooseneck Flatbed w/a GVWR of 14k ,Round trip 3.5 Hrs half empty/half loaded. Empty the Trailer is about 5k,he does'nt say how much the attachment wieghed.

oh - well that does suck a little bit

[Blueox01]

oh - well that does suck a little bit

Take that back,he's from Canada says it's 14000kg,not sure what that in LBS.

[JOHNFAK]

Take that back,he's from Canada says it's 14000kg,not sure what that in LBS.

2.2 lb to kilo Its rated for 14k kgs tho right - 30000 lbs. But if its empty - then its only towing 5000-7000 lbs and pretty low drag resistance ?? Didn;t catch if he towed anything back apart from an attachment - so what was final weight ?? Was it 3.5 hours of mainly empty ?

[flagmanruss]

I'm always a bit surprised at the drop in MPGs with my single axle landscaper's trailer... empty. I've greased & readjusted the wheel bearings. Grease was fine & they were not too tight. It's not as bad as the horse trailer or ToyHauler (Huge flat front, worst). It would seem that turning a 4 extra bearings should not be that much drag.

[dobienut]

Sorry guys, haven't had much time to check in the past couple days...i'm pulling a 16 ft bumper pull with 15 inch tires. Running the XZT programmer on my truck