Help with my MPG before i throw in the towel

Tire type more than size is more important in relation to fuel mileage. You never mentioned what tire type and model is currently on your truck. Fuel Saver tires with low rolling resistance ratings cost more money to purchase, but pay for themselves in no time over a lug type tire and may I suggest a tire pressure sensor system to monitor tire pressures ($400 to $600) that will not only pay for itself with the cost of one roadside service call along with allow you to maintain high tire pressures to get the maximum fuel mileage and maximum life out of your tires.

Michelin has a great fuel savings calculator that you can use to find the best tire for you here: http://www.michelintruck.com/michelintruck/toolbox/FuelSavcalculator.jsp
Compare with your current tire and remember fuel saver tires cost more, but the payback is very fast.
Here is also a good information page from Michelin on tire rolling resistance including other losses: http://www.michelintruck.com/michelintruck/tires-retreads/xone/xOne-fuel-savings.jsp

Alot of people over look a 3 axle alignment around every 6 months that can make a huge difference in fuel mileage and only cost around $200 to $250 at most shops. Becareful on this to find the best alignment shop with a great reputation and this I have found is usually not where you buy the tires (atleast in my case). My regular shop has a Hunter lazer alignment system that appears to the best I have found and if done right, you can feel the difference as soon as you drive it off with less rolling resistance.

Invest in a good temp gun for around $36 from Harbor Freight will allow you to check temps on everything from bearing hubs to brake drums for rolling resistance robbing friction. Here is the one I use: http://www.harborfreight.com/infrared-thermometer-with-laser-targeting-non-contact-69465.html Most used tool on my truck.



You can also check tires with temp gun that don't have sensors. Usually the hotter one needs air for quick tire checker.


I believe an overhead should be done atleast every year or around every 100K miles to keep the truck tuned up and like alignments, you need to find a shop with a good reputation that you can trust it will be done right.

As said earlier, slowing down and run the least boost possible to still move the load down the road. My 98 Cat powered Volvo 770 with Michelin Super Singles (125 psi) runs down the road at 57 mph average at around 1,100 rpm and almost 0 boost on flat ground with the larger Pittsburgh Power (BW) turbo and better flowing custom molded exhaust manifold (they also offer for the Detroit motor) at around 9 mpg (my 2012 average was 8.99 mpg).

There is alot of things that effect fuel mileage that do require an investment of capital that I need to remind you it takes money to make money. These are just a few of those things that make a difference and there is more from synthetic motor oil to Fleet Air Filters to Airtabs to the FASS to even MicroBlue treating everything that causes friction and let's don't forget Walker Megaflow mufflers. There is alot more than these and as mentioned earlier by listening to Kevin Rutherford's radio show will make you money by getting that fuel mileage up. I don't 100% agree with everything he says, but in general most of it will make you money if take most of his advice.

Good luck and God Bless!

 

Let me add to this since I posted last I moved an Oversized power only trailer that after 600 miles I had 1 brake drum 35 degrees warmer that I adjusted that slight rub out of the brake and picked up over 1 full mpg. That was even more because I went from the flat lands from FL to NC into the mountains of VA, PA, NY and CT and still gained mpg.

Amazing how much the temp gun is helpful in finding a little brake rub that robbed that much fuel.

 

+! on the temp gun. I rediscovered mine this week. My new to me truck has drive axle temp gauges that appeared not to work. Monday I'm cruising thru AL and out of the blue the rear drive temp is reading 155º, but the front drive is still looking dead. 155º isn't alarming, but I was worried about the difference. As-in maybe it's really a lot hotter or something to make the gauge suddenly work.

I got my temp gun out and both diffs read 155º. So the rear gauge just woke up and nothing abnormal. Then of course I proceeded to shoot the temp on all the hubs, tires, spots on the pavement, my shoes, everything LOL. All normal BTW.

One interesting data point however. When I bought this truck it came with 7 matching recap drives (Bandag Megatrek) with about 70% tread and one really worn (apparently blowout replacement) tire that was on the RFI position. Before I put the truck in service, I had a new matching one mounted. The temp on the new tire was 20º warmer than the 70% one on that pair. I'm running cat's eyes on all tandems, so the pressure is balanced. Surprised me to see that much difference from only a minor tread depth difference. All the other tandems had the same temp on both tires, even one on my trailer that has a mismatched pair. Although that pair is probably closer tread-depth-wise than the drives. Gross weight was 75k so that may have played a factor with the drives as well.

 

You are right the engine wants it. its a detroit 1450 to 1650 dong go lower than that or you will drop more mpg. first question what turbo do you have if it has a waste gate dump it for a non gated turbo but for time being pull off the exhaust side and make sure that gate is shut than plug the vacum line so it will not open. that will give you better mpg. how is it pulling on the hills as that is where most mpg are lost. some specs would really help here. i see you asked about tire size. that can play a factor to. an 11r24.5 will give you more speed but cut your power down badly out of the 4 common tire sizes you have 3 different ratios meaning lp 22.5 power tires 11r22.5 and lp24.5 mid power speed ratio and 11r24.5 speed. need to match tires to rears and tranny note 11r22.5 and lp 24.5 give the same ratio as they are the same height tire....

things to help mpg
gateless turbo
port and polished manifold
turbo blanket
ecm tune
aftermarket injectors
proper tranny rearend and tire mess points ( meaning everthing is geared together for power and speed for what you will be running)
trailer gap helps some never had a big diffenence though minor results over long term testing

you could bit into the slope nose hood line I dont I get 7 running hard and heavy out of a 96 classic with a 12.7 detroit I will tell you the biggest changer for me was turbo I had to bolt on a gated turbo to finsh off a week intill the new one came in and i lost 3 mpg. the port and polished manifold will keep egt down and allow smooth flow of exhaust and the blanket will keep egt temps level to help keep exhaust gas flow smooth. ecm tune will get more power as well as everything else i listed. More power less time on pedal getting up to speed and up hills equals quick increase in mpg. than factor in driving habbits like getting on the fuel before the hill slope and not letting the cruise do it for you when its to late....will get you even more mpg....

 

that new tire carrys more weight than the rest so it has more resistance than the others hence the increase in temp

 

I run over 70 all the time and get 7 mpg......and thats with a classic

 

Actually, it carries exactly the same weight as the other tire on that tandem since the air pressure is exactly equal. The deeper tread and unequal sidewall flexing causes a tiny misalignment, more rolling resistance, friction == heat. Not enough to pop a tire, but I won't be surprised to see strange wear on that pair over time.

 

Get your airdryer problem fixed yet? Might not help mileage much, just fix a known problem with the truck. Anyway, I would urge you to check out Airtab.com. Some salesmanship on the site, but a lot of truth also. I installed them according to instructions on my 88 Honda Accord and went from 30 mpg to 32 mpg on my 17 mile rural highway commute, with no other changes. Talked with several drivers that run them and they report improvements in fuel economy as well as stability and visibility in rain and snow. Not magic, won't add 50% improvement in mpg, but they will usually pay for themselves rather quickly, then let you keep more of your paycheck. Some applications such as box van or reefer will see bigger improvements easier, but I believe most high speed applications will see some benefit. Sorry for going so long, just my $.02

 

Are you running on synthetic oil? any additives in oil or diesel to get this mpg?