The Mothership needs an MPG Boost

[Rawze]

(05-18-2016 )brothermothership Wrote:  Hey all, I am currently driving a 2016 Volvo 780 that pulls a flatbed at or near 80k most of the time. The combination is as follows: Cummins ISX15, Eaton Ultrashift + 10 speed overdrive ( .73 ), 3.36 gears, standard profile 22.5 tires, 450hp with 1550/1750 ST rating on the plate.
The vehicle has about 25000 miles on it, no trouble codes, and in general runs ok. The emission system is working fine. Despite all this, the fuel economy is not acceptable. I've tried driving slower ( 56 to 65 mph ), use the cruise as much as possible, and in general be kind to the Mothership. The best it's done is 6.5 with a load of straw from ND to TN that was tall enough to help with the aero and was 33k# ( about 67k gross ), but most of the time it's 6.0 to 6.3. I don't idle the truck much.

I did notice that the transmission programming was not optimized for best fuel economy, and the Eaton rep is coming out to put a low rpm/progressive shift program in the ecm to bring the revs down to 1500 or so rpms and to skip gears instead of running through all of them. The engine speed load breakpoint was lowered slightly to 1600 rpms. When it gets serviced again, I am considering going to a lighter oil like a 5W40 to reduce the drag. The trailer was out of alignment so it's getting replaced with a new Reitenour. I am also going to check the tractor alignment to make sure it's ok.

Are there any other things I should look at? How does the ISX respond to the lighter oils? Should I be concerned with cam and valvetrain wear? Thanks in advance for everyone's help.....there are 5 trucks similarly speced that are hanging in the balance.

Do not take this personally -- Just making a point here... Just my own thoughts bad as they may be ...

FIRST AND FOREMOST!!! --- WHO IS THE MORON WHO SPEC'D THOSE TRUCKS!!!???


FIrst of all --- Volvo trucks have a HORRIBLE engine compartment design that is OFF THE TOP --- 0.6 MPG LESS FUEL EFFECIENT THAN ANY OTHER BRAND OF NEWER EARO TRUCK! -- Simply because they have restrictive charge circuits AND horrible design of exhaust flow!.-- PERIOD!--- So you can count on one thing for the whole life of those trucks! --- THEY ARE GOING TO LOOSE FUEL MILEAGE COMPARED TO OTHER EARO TRUCKS IN THAT CLASSIFICATION!. Hell,.. I can fit the turbo and other piping literally inside the piping of even my POS prostar it is so small and restrictive,... YES, they are that bad!. The turbo runs 100 degrees hotter because of poor engine compartment air-flow external to the engine, and that makes the oil run hotter as a result. It is easy to have one running around at 235 F oil temps and it will constantly be in silent derate (lowering its fuel mileage a bit more). The list of problems with Volvo trucks is long, yet everyone seems to love them because they don't look past that interior on them. It is truly a shame. -- The sad part is that everything I mentioned could be fixed by slight design changes to them,.. but I don't think the the Volvo truck company realizes what they have done, or perhaps they are simply too cheap to do things right?.



Next --- They have Autoshiftas !!1--- Another 0.6 MPG LESS FUEL EFFECIENT OFF THE TOP COMAPARED TO A STICK AND A DECENENT DRIVER! --- So now your DOWN 1.2 MPG off the top when you combine those 2 facts!. -- Over the next million miles,.. it will consume about 27,000 gallons more in fuel just because of what you have spec'd, not even considering the tall rears you have there that it has to fight as well.


Next --- WHY WOULD ANYONE SPEC 3:36 REARS!??? -- In a truck that is going to move heavy freight -- ESPECIALLY heavy flatbed freight?-- That is a 70 + MPH spec for dryvan/reefer and is HORRIBLE for flatbed!,.. and the truck has no ability to get out of its own way very well with gears set that tall!-- Again,... load it up heavy,.. and your fighting those tall rears and it will kill your fuel mileage!!!

Next -- I commend you for trying to drive it slow,... BUT with such horrible tall rears and Autoshifts,... your fighting an uphill battle, lugging the engine etc!. The only way you can even start to get decent effeciency out of one would be to fight the Autoshift and drop it into high RPM with manual control! -- What a waste of effort.

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Next is the actual question---

Thinner oil is NOT going to do squat for fuel mileage! -- IT IS A F$$KING MYTH BULLSH$#IT STATEMENT FROM DUMBARSSE THEORISTS!! -- I have tested this myself and have even run up to 2 gallons of 80/90 gear lube in my engine just to see if fuel mileage suffered, then compared it. GUESS WHAT -- IT MADE NO MEASURABLE DIFFERENCE! -- I put one gallon of 80/90 gear lube in my engine at every oil change, and my truck still busts 8.9 mpg all day long!.


Your barking up the wrong tree trying to save fuel with that horribly spec'd truck,... I got a better idea -- GET RID OF THAT THING AND RE-THINK YOUR STRATEGY!!!!!! -- It is clear those trucks were made/spec'd for a 'Haulin-arsse' dryvan/reefer company that was going to be in fast-lane all day. Whatever salesman who convinced you to buy a truck spec'd for something that clearly you are not using them for, is the one who should be paying for your fuel. that way they will not do such horrible things to the next guy who comes along who does not know better.


If fuel mileage is your number one concern,.. (and it should be) -- then you need tyo get rid of those Terribly designed Volvo's (Interior on Volvo's is great, but the engine compartment is horribly designed) and get something that is actually meant to be effecient from the ground up,.. and SPEC IT FOR THE TASK AT HAND!.