How to improve MPG....

Regardless of any other factors, pulling a deck at 75 mph is the single biggest thing that's killing your fuel mileage, not to mention prematurely wearing out your truck. Now, I realize that slowing down from 75 to 60 is gonna feel like you're crawling, but I guarantee that if you back off to even 65 you'll see a substantial increase in fuel mileage. Keep a notebook and record your odometer reading and gallons put in at each fill. I used to pull flats with an '06 Pete 379 that also had a 475 Cummins ISX and I was usually able to beat 6 mpg running at 60 mph. A big plus for me is I found I was less tired at the end of the day, since I wasn't constantly changing lanes to pull out and pass. My truck had an 18 speed, 3.70 rears, and ran on 11R 22.5 rubber. If you do not see a fuel mileage increase from slowing down, there is definitely something wrong with your truck.

 

Once years ago I was coming east on I-40 down the mountain to Needles, CA. All of a sudden a Yellow Freight Truck blew my doors off. I was just easing down the mountain taking it easy, that mountain is not that bad. When he blew my doors off I shifted up letting my truck catch him. He was going the other side of 90 MPH and I had just shifted into overdrive.


I asked him on the old CB, “I surely did not know Yellow had any trucks that would run like that.” He answer me back saying, “Any mountain I come to I kick it out of gear and I let it roll, I let her roll as fast as she will!”


I wonder at time if he ever wound up in a big pile off the side of highway going down some mountain.

 

No, not a big yellow pile, a little yellow pile.

 

I have pretty much the same set up, 06 387 cat c15 10 spd flatbed conestoga
if I run closer to the 70-75 mph mark I get 5.5-6 mpg and under 65 it wil easily jump to 7 and have done as well as 7.5

 

When I first bought my truck, the biggest hurdle was slowing it down to save fuel.

I have a BXS Pre DPF ACERT in mine and the sweet spot for efficient cruising (For me) is 1400 - 1450 rpm. The more I can keep my foot out of it instead of matted to the floor, the more efficient I run.

I bought a boost gauge/manifold pressure and use it when climbing hills. I used to just mat it to the floor just before a hill. Say the speed limit is 70 and I'm cruising at 65. I'd mat it about 1000ft before the hill and hold it there until I made it over the grade. Now I watch the gauges and try to stay out of max boost. Even if it means dropping 2 - 3 gears. I had old timers tell me that the quicker I could get up and over a hill the more fuel I would save. Well maybe for their truck. Not mine.

I've done other things to the truck to help,.. but over all, changing my driving habits and learning to discipline myself has had the largest effect on fuel mileage for me.

Compare to when I first started out and where I am at now.. I calculated 2 weeks ago that I have saved approximately $17,800 in fuel costs to date compared to my first 30 days. Not sure about you guys,.. but $17,800 is substantial enough to get me to keep looking for ways to save at the pump.


Hurst:smt111

 

Something is off mechanically slowing from 75 to 65 puts you at 5 mpg from 4 mpg ... With egr motors it's a guess as to what could be wrong ... Find a good cummins shop and get them to test it

 

Slowing down doesn't work for everybody...it is a give-and-take situation. You are picking up fuel mileage, but at what cost? Time. 14 hour clock is 14 hours, and the 11 hour limit is 11 hours, whether you are running 75, 65, or 55. Many "slow trucks" try to make up that time by NOT slowing down in construction zones, school zones, or when going through towns...which has another potential cost when they get a driving award for not slowing down in these places where their trucks are actually capable of exceeding the speed limit.

If you've got time to spare, then by all means save that fuel...but for me, slowing down might mean paying $75 for a motel room if the clock expires before I complete the run...which means wearing the same grungy clothes another day since I didn't get home where all my clean clothes are. There is also the lost revenue. What loads would I have to drop because I couldn't get to them in time? Does that mean I bounce home instead of hauling a paying load in that direction? What would that load have paid? Did I save enough fuel to cover that loss? For me, the answer is usually "no"...so I run the speed limit in order to complete the run as quickly as the law allows.

Every operation is different, though. I go home every night, and run the speed limit to make best use of my time on the clock. E7-460P Mack engine, T2180B Mack transmission, 4.17 geared Mack rears, with aggressive lugs on 11R24.5 tires...which puts me just shy of 1700 RPM'S at 70 mph, yet goes wherever I need it to go to pick up and deliver my loads. Pulling 80,000+/- every load, doesn't really matter if I'm running the speed limit down the interstate or doing short hauls on 2-lanes with all of the stop & go and slowing down through towns, I have no problem getting 5.75 mpg. Macks are designed to turn higher RPM's at cruising speed, because they are usually spec'd aggressively for the job site and still need to be driveable on the road. Your OTR truck should be spec'd for OTR work...less aggressive gearing and tires better suited for the highway and within your engine's optimal operating range.

Heck, even a truck spec'd specifically with fuel mileage in mind is going to sacrifice in other areas. TINSTAAFL. You might spec light weight components to save fuel and boost your ability to haul more tonnage...but those light weight parts aren't as durable, so your repair budget will increase. You might put super single tires on to save both weight and fuel, but now have downtime in a potentially dangerous situation because you are dead in the water if you blow one out or cut one...not all roads have shoulders, and you can't limp up the road to a safer location (or to a shop to save on the service truck coming to you) like you can with the heavier, less fuel efficient duals...not to mention they get stuck a lot easier any time the directions include "turn off the paved road". Aerodynamic, close tolerances, low ground clearance...all great for fuel mileage, TERRIBLE on a job site, where bumpers get torn off, tanks dented, fenders smashed, etc. I've even seen pencil-pushers spec single screw/dead axle trucks for vocational work trying to save weight and fuel...and when they have to be pulled in & out of every job site, contractors start looking elsewhere for the trucks they need and there just aren't the loads available to keep the trucks busy. EVERYTHING is a trade-off, nothing is free, and every operation is different. What works for one might not be good for another.

Improving fuel mileage is good...but if you focus all of your energy on that one aspect and allow it to harm other aspects of your business, you haven't really solved anything...just moved the problem around a little.

 

Hurst's experience brings back memories of my own experience.

The "Sweet Spot" (best MPG)

For the OP note as my thread progressed I went through a learning process. Testing new driving methods (and using a boost gauge especially pulling hills a la Hurst) resulted in mpg gains from 4 mpg to almost 7 mpg on the run from OKC to St. Louis on rolling hills that can chew up fuel in a hurry if you don't drive for efficiency.

On the other hand Pedigreed Bulldog also has a great point (as many forum members pointed out in my Sweet Spot thread), the effort to save fuel may have an opportunity cost. This will be depend on the value of the loads you pull. A good example would be my brother with that '03 KW T2000 that was my experimental truck getting back into driving. At that time he was leased on with a company that paid him a fixed $1.35 per mile, and his lack of fuel economy was killing him. Fast forward to 12/31/13, when he got the heck out of Commifornia because of CARB and leased on with ACME out of OKC, now his revenue per load increased dramatically. Now his main focus is going "hammer down" to deliver loads quickly in order to get at least one or two more loads per week. When he was only getting $1.35 per mile fuel was everything, now fuel is a tiny fraction of his total cost and it makes more sense to hammer down and get a few more thousand gross for the week with another load or two.

For anyone that is leased on with a situation where fuel economy will be a prime factor for success, I agree wholeheartedly with Hurst. You would do well to get a boost gauge and monitor it especially when climbing hills. Learn to drive without mashing the throttle to the floor. The fuel savings can be surprisingly good.

 

The difference from 75 to 65 MPH for me is roughly 2000 rpm. 75 mph on flat terrain,.. no hills I get roughly 4 - 4.5 mpg (Depends on load). Anything over 1500 rpm and the mpg drops off dramatically. Engine is mechanically sound. Though not a Cummins,.. ACERT motors seem to do much better lugging around at lower RPM's. Mine is happiest between 1300 - 1450. Also with flatbed,.. I can have a 30klb load and get 5.9 mpg,.. then load a different 30klb load and get 5.2 mpg. The load will play a dramatic roll in mpg for me. How tall,.. how heavy,.. how bad will it catch the wind,.. is there a strong cross or head wind,.. all of this has to be factored in. I've had a tall 23k lb load and struggle to keep it above 4.5 mpg. The wind starts rocking my cab,.. I know then that its going to cost me if I dont slow it down. In those conditions I'm the guy doing 60 in the right lane.

As for the topic of time and production vs mpg.

Lets use 70 mph speed limit, running 65 mph. Over the course of 10 hours,.. no one maintains a constant average,.. not even on cruise control,.. but in a perfect world,.. the difference is 650 miles vs 700 miles. You lose 50 miles of production,.. or roughly 1 hour. I do flat bed,.. I dont have appts,.. I dont run on a schedule for anyone. I deliver when I say I will be there.

2 hours of travel time lost over a 2 day period is not going to effect my bottom line one bit. $18,000 cash saved at the pump is beyond the 1 or 2 loads over the course of a year that I may have missed out on.

Hurst:smt111

 

I guess I never got the pressing need for speed after all those years of the 55 max nationwide speed limit. I generally ran around 60 during that time, and I generally run around 62 now, occasionally I will bump to 65 for a while depending on the situation. The states keep jacking up the speed limit, I just cruise along like I have done for decades. It has paid off with the fuel I have saved over the years by not trying to bust that sound barrier.