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Old 09-03-2014, 10:16 AM   #1
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Has the miles per gallon of diesel fuel diminished?

It has been about four years since I towed my 27 FB International with my 2008 Dodge/Cummins 6.7, but as I remember, at about 62 mph, I was achieving 14 mpg.

Now, with my new Serenity 30 RB, having pulled about 1500 miles on this trip, heading northwest, with some significant winds from the west and southwest, I am looking at from 10.5 to 12.5 mpg. Yikes!

I chatted with a fellow at a rest stop who was pulling an Airstream for the past 13 years and he stated the mpg he achieved has diminished in the past several years.

My question is this: For those who are pulling with diesel engines, has anyone else noticed a decrease in fuel mileage over the past few years?
Of course, the wind factor may be entirely to blame, and the fact I am 500 lbs heavier may be the problem. but I was curious about others experience.

I am head east in a week, then back south east so I will reassess the overall fuel mileage once the trip is complete. I was just disappointed to be pulling at about 62 - 64 mph and have what I consider to be poor fuel mileage.

Thanks for any thoughts on this issue.
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Old 09-03-2014, 10:21 AM   #2
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Great question, I look forward to the responses. From personal observance and discussion, I know it's well regarded that ethanol forced on everyone with a gasoline engine saw a decrease in MPG.

Wondering if there has been a change in the diesel formulas as a result of EPA/Government mandating.
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Old 09-03-2014, 10:23 AM   #3
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I haven't seen any kind of difference with my '04 Cummins Ram based on similar towing and weather conditions when using the fuel from the same location.

When I change anything I do get differences though, and the things that I think will not effect me much, seem to effect me the most. Go figure.
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Old 09-03-2014, 10:46 AM   #4
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I tow with a 6.0 Ford excursion and have not noticed any change. In fact I just had both coolant and oil temperature sensors changed because of erratic reading and saw a couple mph improvement.

Anything that influences the CPU can change the fueling ratio. You might have someone you trust hook an OBD2 reader and check the engine settings. Do not take the truck to a dealer, God know what they will do.
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Old 09-03-2014, 10:55 AM   #5
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Bio diesel gives me a lower mpg. You never know the actual percentages. In Texas it is labeled on the pump. But even that is not accurate.

For instance, with single hose gasoline dispensers the State regulators "flush" the line with 5 gallons prior to taking sample.
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Old 09-03-2014, 11:52 AM   #6
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Yes, I plan on having the truck "improved" with more open exhaust and adjustments to the computer settings to improve fuel mileage.

And, avoiding the dealer…. absolutely. One I had trusted in the past may have screwed up mine when they did some repair on the catalytic converter and charged me for something like a "clean flush" which actually may have messed things up in the exhaust system.

Is anyone running a straight through exhaust with a chipped out computer?
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Old 09-03-2014, 12:32 PM   #7
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I lost about 1-2 mpg after the sulfur was reduced in 2007. But have noticed no change in the past few years.

I've been able to get that 1mpg back using fuel additives, but normally don't bother.

I have an 04 1/2 Ram with the 305hp/555ft-lb and heavy duty 4-speed auto (as opposed to the regular duty 4-speed auto). Probably have pulled the triple axle 25,000 miles with it and so far very happy.

Best of luck,
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Old 09-03-2014, 07:20 PM   #8
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I wouldn't think sulphur reduction would make any difference in mileage.

Bio diesel blends will. And summer vs winter blends will.

But the largest variable remains the driver.
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Old 09-03-2014, 09:37 PM   #9
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I once owned a 1998 vw jetta tdi and was able to pull down 48 mpg on a regular basis. When ULSD was introduced the car would never get better than 44 mpg.
Winter diesel will drop my Dodge diesel by 2 mpg.
From what I have read the biodiesel will also drop mileage.

Deleting the emissions is supposed to help by 2 or 3 mpg amount other improvements.
You may not like the straight piped exhaust as the drone can drive you crazy.
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Old 09-03-2014, 09:59 PM   #10
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Old 09-04-2014, 04:15 AM   #11
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I haven't noticed any great reduction in my diesel mileage. But a variance of 1-1.5mpg is negligible in my book on the truck. I typically get in the 14.5-15.5 range anyway with my 7.3 PSD 4:10 gearing DRW, CC. It is a heavy beast and not geared for maximum mpg anyway. I did talk to the guys at Gale Banks a while back and they recommended a larger exhaust, better air filter system and an upgraded turbo housing. IIRC it was a bit over $2500 at the time, should get a 10-15% increase in mileage, plus some power gains, again not really huge on a 15 mpg truck. I passed on it for the time being, the truck has only been getting 3,000-4,000 miles a year put on it at this point.

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Old 11-04-2014, 11:15 AM   #12
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Has the miles per gallon of diesel fuel diminished?

Most operators noticed a diminution in mpg with ULSD. I now use Power Service in every tank and only Esso or Shell diesel. MPG is back at what it was and occasionally better.

The rule for best economy in a CTD is 666: 6-psi boost or less; 60-mph or less; and 600F egt.

Don't assume truck or TT alignment is perfect, verify. Same for bearing preset. Brake drag on both. Steering gear slop. I'd also recommend KONI FSD shocks. Closed shoulder highway rib tires are best for FE and longevity. The champ is currently the Bridgestone Duravis m500

. I've added a small anti-roll bar to the rear of mine (and increased the size of the front one). A Panhard Rod (also called Rear Track Bar) are other additions to reduce steering wander. TT tires to sidewall max pressure and TV to best pressure versus measured load. FE is a about the small things adding up.

Of course, FALR on a Dodge is a good idea. As is a Pro Pride hitch.

A pre-emissions CTD can pull a bigger A/S at 14-16 mpg with the above nearer to 60-mph. Have found around a dozen other examples in South Central US


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Old 11-04-2014, 11:29 AM   #13
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Quote:
Originally Posted by slowmover View Post
Most operators noticed a diminution in mpg with ULSD. I now use Power Service in every tank and only Esso or Shell diesel. MPG is back at what it was and occasionally better.
Which Power Service do you use?
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Old 11-04-2014, 11:40 AM   #14
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Power Service Silver.

Also the tank cleaner formulation every so often.

Lubrizol came up with a new additive that cleans injector interiors not just tips. PS uses it.

The others are all okay but Schaeffers 2000 is the one to have. I'd use all their products throughout the truck but lack storage space for bulk. Worth ordering (as I used to do on all our vehicles).

5W-40 synthetic engine oil allows my engine to turn over more easily even down south here in Hades. Rotella posts the best numbers according to the tribologist I consult. Donaldson Stratapore oil filters and MOPAR deep air filter.


Need to add that fuel filters should be changed ahead of schedule (Baldwin only on CTD)

Plug in truck coolant heater year round is another nice as to reducing engine friction. Can be seen at pump. 90 minutes to 115F.


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Old 11-04-2014, 01:12 PM   #15
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Quote:
Originally Posted by Msmoto View Post
My question is this: For those who are pulling with diesel engines, has anyone else noticed a decrease in fuel mileage over the past few years?
Of course, the wind factor may be entirely to blame, and the fact I am 500 lbs heavier may be the problem. but I was curious about others experience.

I am head east in a week, then back south east so I will reassess the overall fuel mileage once the trip is complete. I was just disappointed to be pulling at about 62 - 64 mph and have what I consider to be poor fuel mileage.

Thanks for any thoughts on this issue.
Hi Msmoto,

I do not currently pull using a diesel power train such as yours, I am a diesel tech and fleet manager that uses the Cummins B, C, M, and X, among others.

Yes there are many variables that are just too subjective to distill a definitive answer with some trends to graph. Very generally, AIR FIRE FUEL.

AIR: reference to condition and ability of the base engine to pump and power.
FIRE: reference to combustion
FUEL: reference to agent used to create the flame event

They are interdependent; the greater truck is an interdependent machine with the power train as it's heart.

Let's explore a scenario: a diesel power train such as yours averages x over y time fuel usage to provide you a fairly steady, normal level of performance. You're satisfied until fuel economy starts to suffer, and it's of note enough to discuss. As a tech, the systems pre-checks such as tire pressure and condition, axle alignment, service/parking brakes dragging, even just a little due to debris build-up, clean and clear engine air filtration, clean and clear cooling package fins, engine coolant condition, coolant thermostat cycle time, DPF condition (logs of cook cycles, which require fuel, like a self-cleaning oven), fuel system condition and fuel quality, any aftermarket modifications such as lifts, tires, software mods, unnecessary cargo weight...to name a few things you can do yourself.

A customer with a 6.0 years ago had a similar issue. No codes, steam, burping, ran great. It ended up being a twinkie wrapper partially blocking the big Donaldson air filter intake. Another had a 6.5 Detroit turbo diesel that was experiencing higher than average fuel consumption, with ended-up being dragging service brakes. Finally, a late Ford SD 7.3 owner was distraught that his puller had descended into the 5-6 mpg range within a 4 week period. The base engine had very high crankcase pressures, and was near the end of its service life. It kind-of was a learned compensation on his end...more and more throttle, then a spate of diesel fuel price spikes. It still pulled well (by his standards, but once in a newer unit on the lot he understood how much he had been flogging a worn-out engine. Likely not your problem, however a sensitive, observant operator notes fuel consumption, which is you.

Hope this provides some mental carrots.
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Old 11-04-2014, 02:30 PM   #16
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Excellent post!!

I forgot about the hoses to the CAC


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Old 11-04-2014, 03:15 PM   #17
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Once you get out of the mountains, I can roll 14 mpg down I-77 headed south with the AS, consistently. Its always less coming back home. It will be less here at the end of the week, I had to put the BFG's back on. They do not roll as easy as my old Michelin's. I finally wore them out. Well more specifically they are ten years old and have some substantial cracks in them, so I put the BFG's back on.
Next time Costco has the rebate on the Michelins I plan to get a set.
Haven't really noticed a decrease in fuel mileage.
I try to do everything 'Slowmover' recommended, except I don't have th eheater for the coolent. I keep a trickle charger on the batteries and use the Hastings air filter, Fleetguard fuel filters. I like the Rotella synthetic oil, its very good.
I have the deep transmission pan and aluminum PML rear differential cover that adds extra oil (synthetic 75w-90), recommended in the AAM axles.
4.10
Just changed the coolant in preparation for this two week trip coming up. It was time. I have a special brush for the inter-cooler fins.
Have been adding the Power Service cetane boost and 2 cycle oil every now and then since the EPA removed all the sulfer. Diesel fuel has come down a bit in price.
'Big-D' has been steady on fuel mileage. It does great when not towing, if you can keep your foot out of it
Have a good one !
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