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Have a 2014 cxu613 with a mp8 rated 505 hp pulling a 48 ft tandem flat bed. Problem is fuel mileage, at first I thought it was just that I was encountering more wind then normal. Now I believe there is something wrong. I just ran from Florida to Edmonton Ab with only 6000 lbs on the deck and only got 7 mpg and top cruise speed was 65 mph. Last few trips between Calgary and Denver with gross weight between 76 and 79000 lbs I've been down between 5.1 and 5.3 mpg and on the flats I set cruise at 63 mph.  I feel this should be at least 1 mpg better. Any ideas. Called my local dealer but he has not called back yet. 

Edited by Bigl62
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Tell us more about the spec's on the truck.  What kind of tires on truck trailer?  Pressure etc....   all of that stuff adds up to the final number.   I'd be shocked if the shop can do anything for you.   I'm  certain their skin crawls when someone comes through the door with a fuel economy issue. If the check engine light isn't on, they have no clue where to start.  Btw 1 or 2 trips doesn't tell you much.  You need a 30/60/90 day average.  Miles divided by gallons.  Now we have some solid numbers to make a decision on how bad things really are or if it's just a matter of a bit of tweaking required.  

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fellow Canuck...

can't answer your question, just asking which gallon you are using?... I assume USgal, using Imp gal would throw off the number... of course, litres per 100km would confuse this audience...!!! LOL

and as said, one trip is not going to give you good stats as there are so many variables... gearing, tire size, rpm for instance... and your driving style.

did you just buy the truck or did something change recently??

BC Mack

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  • 2 weeks later...
1 hour ago, ezxpress said:

I run flat ground with a 2011 cxu 613 and cant touch or smell over 5.4. New injectors and cups, with a automatic and 65mph. I dont understand. 

Your speed a large factor along with rolling resistance of tires and type of trailer. The difference between 55 and 65 mph is almost 1 mpg. 

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Running a 95 CH 613 , E 7 350 pulling flatbed , OH, KY , WV, IN. 30 day avg 6.57 mpg, but just discovered I have a leaking charge air cooler. I have been running loaded about 85% of time, when loaded miles drop to about 50℅ usually about 46k on the deck. I was averaging 7.1, hope new charge air cooler helps, hasn't had overhead ran in years, I only run about 60 mph.

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He has a radio show, he's big on fuel economy, talks about rolling resistance, aerodynamics, slowing down to 55, etc. I enjoy  listening to him, I guess it's all common sense though really, he brings in guest from Pittsburgh power, I've listened off and on for years and only heard them mention Mack one time. He said he did accounting at one time for drivers and noticed Macks in the late 90s to early 2000s got excellent mpg, he actually called drivers thinking they were losing some fuel receipts, but all they really promote is 12.7 Detroit for fuel economy as the best, seems like Cummins second. Pittsburgh power won't even work on a Mack or Volvo engine.

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Bigl62 Do they still make Howes fuel additive? I got improved fuel economy using it! Was that 6000lb load a high tarped load of insulation? Are you pulling an air ride trailer that you can raise one axle in good weather  with a light load? Many variables as someone mentioned!

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I'm curious how much the fuel additives help in older engines, was told once the improvement in fuel economy wasn't enough to offset the cost of additive?

Depends on your fuel supply. If you are confident that you are buying good quality fuel at all times, that greatly reduces the benefits of any additives. Years ago when I was buying my own fuel, I shopped price more often than the big truckstop chains. Small Mom & Pop fuel stops maybe greater risk of water or other contamination. I ran Lucas and Howe's for a while, but did the math and finally settled on Power Service products, best dollar value and highly recommended by my supplier. Enough MPG increase to justify use of the product, plus peace of mind regarding contamination and cold weather protection. Ran my 2000 CX 1.5 million miles never replaced an injector.
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We see lots of split aftercoolers on GU and  CHU's. Usually  the bottom tube is blown out. Pull up your boost guage on your GuardDog display and see what your boost is under are a hard pull. Should be at least low to mid 30's and as high as 42.  A sticky VGT turbo, a bad boost pressure sensor or a problem with your EGR valve/ flow sensor can cause poor MPG. My buddies 505 plus CHU with 3.21 gears more or less idles down the interstate at 1250 rpm. He gets in the 7 mpg range and the day I rode with him , he Grossed at almost 99,000 pounds. From what I have seen in the last few years , it's all in the rear gears.  The MP 8 engines have the power to to run the high gears now.  A logging customs here has a 505E CHU with low rears gears for use in the mud and woods. The paper mill here closed a year ago so now hes hauling different products and mostly interstate. The 1700+ rpm is killing his mpg.  I think 5.2 was his overall and 5.7 in cruise. Gotta get thoses RPM down

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My truck is 95 E7 350, 4:17 rears , I run probably 50℅ two lanes and the rest interstate, run 55 on 2 lanes and about 62 on highway. At 62 I think I'm around 1600 rpm, I have a scan gauge that measures mpg, it's not 100% accurate so I still calculate every tank fill. The rpms don't bother my truck that much , the main thing I found is boost , if I can keep boost low, regardless of rpm I can get good fuel economy, of course this is an older engine, may not relate to MP 8s . I'm still hoping I can get this thing to avg over 7. You would think it's only 11.9 litre engine, and I'm lightweight, maybe possible.

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  • 1 month later...

Hello everyone.

I have a 2009 pinnacle with the 485 hp MP8 with A 13 speed fuller and 355 rears running on 22.5/11 Michelins  and I regularly pull 50,000 to 75,000 pounds in the box and I run 60 mph at 1300 rpm and I get 5.7 to 6 mpg based on 3.7 liters equals 1 US gal. if I haul a light load of 30 to 40,000 pounds my mileage goes up by 1/4 to 1/2 mpg. my tanks hold 180 gallons and I fuel at 1/4 tank and put in approximately 160 US gallons. I too would love to get into the 7 mpg range. Did this only once with 25,000 in the box.

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  • 1 month later...

There are several ways that can help improve your mileage. From simple maintenance like changing the air filter and checking for boost leaks to adding aftermarket products like the fass fuel system and Airdog, you can get a slight improvement in mpg.  Try to use the search function for other mods.

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  • 3 months later...

 

More info on the truck,  3:55 diffs, 18 spd, 22.5 Hankook dl12 tires, 670,000 km. Just had valve set done (said back 2 out by 40,000). I do calculate mpg by US gallon. Long term mpg is 6.2 (from truck readout).  

I've found that keeping engine load at 75% or less I can improve an estimated .3 mpg better. Running elog now and governed to 65. With elog I find I'm rushing more now so running less than speed limit doesn't make as much sense to me. 

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  • 1 year later...

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