Prime drivers, lease operators speed and mpgs

I think that speed is going to give you optimal fuel mileage. That's one of the reasons I bought a new 2015 Evolution, recently. Anywhere between 62-65 mph is good. So far I like this truck. Very comfortable and there's plenty of power of this Detroit 500 hp unit.
Good luck.

 

I've topped my fleet doing 57-58 mph in my. 14 Evo

 

Yes it does, but if I want to take the instructor class I need to keep my speed and RPMs down. ( per my FM)

 

The nonsense about a one, fixed, never needs to do anything else "optimum speed" is a bunch of hogwash. You want some proof. Do your optimum speed routine on the 20 miles of I57 south of the I80 interchange near Chicago. That chip 'n seal surface will suck 4 mpg easily out of your "optimum anything."

30% of fuel economy is due to drive technique... so I imagine anyone who knows how to drive can get much better than 8mpg out of your truck. You're running a 10-speed with 3:42 rears... a much better speed for fuel economy is achieved in the 50's. Want some proof? Grit your teeth and run 57 for a couple of weeks. You'll gain 0.5 mpg. Everytime I need some speed for schedule purposes and set my cruise at 62 my per-tank fuel economy drops into the upper 7 mpg range from mid to high 8's.

So... since technique is so important, grab a notebook, ruler and pen... and start a fuel log. Note the trip, date, locations along the way, split the trip up into convenient legs, write down your fuel consumption for the leg, distance... and calculate your fuel economy for each leg and the entire trip. Do it religiously, and you'll start getting a real idea of what your truck is doing, how it's doing it, and what you're doing as well. Just looking at your ECM gauge and guessing is just guessing. Vary your driving technique to see what works and what doesn't... keep the stuff that improves it, and discard what doesn't. IMPORTANT... only change one thing at a time! Give it a couple of weeks before you move on to something else. I raised my fuel economy (Century Class with a series 60) from about 6.3 to over 7.5 doing this.

I recommend getting a ScangaugeKR as well. It's about $200, but it will give you instantaneous feedback from what your ECM calculates is your fuel economy. Well worth the investment, and the feedback it gives you about driving technique will pay for it within a couple of weeks.

Here's some other stuff...

Tire inflation is crucial. You can loose up to 0.5 mpg with underinflated tires. It's especially bad this time of year, because going from a warm day to a cold morning will cause the air in your tires to become more dense, decreasing the pressure. Gotta get out on the cold mornings and check it with a gauge. Prime recommends 110, but I run mine at 120. It stiffens the sidewalls so there is less flexing and less energy loss... I've never had much of wear problem from this.

Trailer balance. Hauling around a arse-heavy trailer will kill your mileage as well. It's best to get the weight distribution as close as equal as you can between your drives and tandems, with the excess always going on the drives.

Trailer tail... it's worth over 0.5 mpg. But only if you deploy it.

Tires... don't cheap out on your tires. The Michelin X-line D drives are a little expensive, but the rolling resistance is low enough that the fuel costs you save will more than pay for them EVERY YEAR.

Remember the "always use the cruise control" line they feed you? Good for rookies. It has a narrow proportional control band that's great on flat ground. Get into the hills and it wants to go full power or nothing. That wastes fuel. Learn how to run the hills on the pedal. Apply some power as you approach the hill to get past the turbo spool-up lag, hold it until your nearly at the top, and let your momentum carry you over the crest. If you have a downhill grade on the other side, let gravity accelerate you to the speed limit as you go down, and repeat.

Mountains, add some speed for the moutains so you have extra inertia on the heavier hills.

Long grades... there's two ways to get up the hill, but both require more torque developed from the engine. The fuel inefficient way is to put your foot into it and pull a lot of turbo boost... which is also a poor man's fuel flow meter. More air (boost) requires more fuel. A lot more boost requires a lot more fuel. You don't have a CAT under the hood so don't bother trying to keep up with 'em! The other way is to use a moderate amount of boost, downshift sooner and use the transmission to multiply your available torque by downshifting. Yeah, you go a little slower up the hill, but you'll save a lot of money. BTW, don't worry so much about your RPMs... turbo boost has a lot more effect on fuel economy than your RPMs. I try to keep it limited to 10 PSI as much as possible.

If you're a lease op, get yourself routed into a terminal and take the ACE-II business course ASAP. It will help you run your business, and teach you how to read your settlements.

About the 80,000 to 100,000 mile point on your truck, get into Springfield and take your truck over to Central Detroit for the Freightliner guys (just up from the terminal on Kearney) and have them do the overhead. We have a deal there to do it for $250... not sure about what it costs over at a Cummins shop. Don't ever let the manufacturers shops touch your engine... they're great at fixin' general truck stuff, but they don't do enough engine work to be really good at it. Getting the overhead set early will give you a serious performance boost and your mpg's will reflect this.

There's some tips to try...

 

I dont think there is one particular magic number with speed that good for all occasions and all terrain. I wish it were that easy. But i know for sure that when i go 63(only when there NO other way) vs 58(my normal speed) on flat ground an 8.5mpg will drop to 7.5mpg for the day in a hurry. Also have an evo on the company side so a dd13 but the evo seams to really shine on its fuel mileage best in the 50's on flat ground. The mountains or rolling hills arent so simple as to one particular set speed.

 

The you have a broken truck. Get the overhead set and the charge air cooler tested for leaks.