Help!! C15 twin turbo MPG...

Discussion in 'Trucks [ Eighteen Wheelers ]' started by Jeron379, Aug 15, 2009.

  1. Jeron379

    Jeron379 Bobtail Member

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    Aug 15, 2009
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    New to the board, looking for some advice..
    Found this site a few days ago, and have done lots of reading.. excellent stuff...
    I have a 2007 379 flat top C15 pre-emission twin turbo.. 18sp, 22.5, 3.70 rear.. I have a large roof top wing on the truck (not sure if this is actually helping me) as the truck pulls a tandem dry box.. avg gross is around 70,000lbs.
    the truck normally averages 5.2-5.4 MPG Over the course of the last month for so its dropped off to around 4.6mpg.. the truck feels lazy other than that not showing any mechanical difficulty.. truck has 330,000miles and has never been touched... since finding this site ive considered adding the fuel temp wire, and some free flowing mufflers..im just concerned about the sudden drop i just noticed before trying to help it... any suggestions on where to start?? my local dealers are not much help in this area...
     
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  3. Jfaulk99

    Jfaulk99 Road Train Member

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    I think these are very particular having the overhead ran and if it's never been touched in 330k I'd say start there.
     
  4. Jeron379

    Jeron379 Bobtail Member

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    thats what i was thinking... some people i talked to say dont bother unless it starts working poorly.. some say do it at regular intervals.. its not a cheap process in my neck of the woods..
     
  5. Donk

    Donk Have a Cup Of Concrete

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    Overheads should be ran periodicaly. specifically to ensure the clearances are kept within the correct tolerances, as parts wear.

    there is a guideline from most engine mfgs, as to how many hours or miles between overhead adjustments. generally whichever ocours first is the time to do it.

    Both my C-12 and the Cummins Sig responded to corectly set overheads.
     
  6. Jas

    Jas Medium Load Member

    Agent86 is right, the overhead should be done at the first 50000 miles, then every 250000 miles after that, more often if the engine works hard all the time. All cats at the moment are having issues with intake valve recession, so overhead adjustment is more important than ever.
    A few other things to check are air filters, fuel filters, waste gate, and aftercooler for leaks, all will give a drop in ecomony and make the engine sluggish.

    I would fix the problems with the engine before modding it.

    Nice pics Agent 86, is that an Aus truck? it looks yankie but towing tri axle trailers makes me think it may be Aussie.
     
  7. Donk

    Donk Have a Cup Of Concrete

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    Its Klos' W900B 007. Its lhd but towing klos lounge trailer.
     
  8. dirtyoldman

    dirtyoldman Light Load Member

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    do the overhead.

    free flow mufflers

    The wing could hurt, but if it was not just installed with the corresponding loss of mpg, would not worry about it.


    Question about the Canadian rigs.....I run in an area with allot of Canadian rigs, and it seems that there are a fair amount of those fancy flattops.

    With fuel being so much more expensive up there, why the fancy rigs, why not a more fuel efficient aero designed truck. 1mpg is allot of money in your pocket, or out of.

    K
     
  9. Jeron379

    Jeron379 Bobtail Member

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    Aug 15, 2009
    Moncton New Brunswick
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    This particular truck was just a good deal, the way i got into it etc. Its not my first pic for efficiency thats for sure...
    I would be happy if it would do 5.2-5.4 avg.. I think its capable and its been close but suddenly its waaay off..
     
  10. dieselroarmt875b

    dieselroarmt875b Medium Load Member

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    it could be your ivt system thats messing around
     
  11. pullingtrucker

    pullingtrucker Road Train Member

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    As Jas said check out the boost side for leaks. The common leak is around the clamps on the intake bellows. Most shops will pressure test these and just give a pass/fail diagnosis. This is bad...you need to know the actual amount of leakage (if any). During the test the shops will only pressurize the system to about 30psi, which is to low for the ACERT CAT motors (stock motor will push over 45psi). To do the test right have the pressure raised to at least 40psi. If the shop won't do this just leave and get the material to do the test yourself. If the clamps are the smaller diameter ones and are leaking, just get rid of them in favor of the larger diameter (around 3/4 inch) spring clamps.

    Also have you addressed the fuel restriction issue. This could also be a factor in you MPG loss if you don't service the fuel filter much.
     
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