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  1. #1
    Sr. Mechanic dadngt's Avatar
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    Default Anyone else have a change in MPG?

    When I bought my truck used a couple years ago it would pull 18mpg about 200 miles on half tank with my regular driving habits. Then seems since fall last year my mpg has dropped to 14-15 range about 180 miles on half tank with same driving habits. Now I've noticed that I've been able to skip the gas pump a few days each week instead of having to go the same day every week. This morning I filled up & to my surprise I pulled 17mpg with the same driving habits. Which I know the summer fuel usually costs more because its susposed to be better, Could that be one reason my mpgs are up & down? Just wondering if anyone else has noticed this in their trucks.

    Still need to get a tune to get back up in the 19-20 range any suggestions?
    2007 Silverado RS, 4.8 V8, 2WD
    Flowmaster Super 44 with turndown
    Black painted front grille & bumper
    Black / red Painted bowties
    Black 18in. Silverado wheels
    Black / Red interior conversion (in process)
    89 Chevy Sport tribute decals

  2. #2

    Default

    All my vehicles respond to summer/winter fuel blends for the first month or so after the changeover I'll get different mileage, this new truck is no different than the rest.
    The only vehicle I've never had a problem with is the boat, I never use it in the winter so it's normally got summer blend fuel in it.

  3. #3

    Default

    Summer/winter blends do appear to produce different mpgs; I wonder, is it the blends, or the air temps that make the biggest differences.

    The into of alcohol into the gas (10%, 15% mix) will lower the mpgs. Alcohol has around 10% less energy than gas, resulting in an appropriate reduction in mpg.

    You may also be suffering from a little wear and tear on the emission system. If getting close to needing a new set of plugs, changing the O2 sensor(s) at the same time will usually result in an improved mpg.
    Ray

    '09 Avalanche LTZ - Black
    '05 Envoy XL (sold)

  4. #4

    Default

    Yes, the summer/winter blends will result in different MPG ranges. For me, I lose about 1.5 to 2MPG with the winter blend. It "magically" gets restored around Memorial Day. This, incidentally coincides with the annual "they're raising the prices in anticipation of people going on vacation!" comments that usually occur when the summer blend kicks in.
    2006 Vortec Max 1500
    Performance:
    -Custom Tune (389HP 440 Ft/lbs Trq - Dyno'd) | Volant CAI | Magnaflow Dual-in/out Exhaust w/3" stainless pipe tips | Fully Built Transmission w/ Red Eagle Clutches & Kolene Steels w/ Corvette Servos and Stage2 Shift Kit | 35K Tranny Cooler | Mobil 1 | Royal Purple Rear Diff
    Other:
    -Spray-in Bed Liner
    -Premium Sound w/lifetime Satellite Radio | Leather | Sunroof | Heated Seats
    -Limbstriping from USING the truck (those are badges of honor)

  5. #5

    Default

    I definitely think the air temps play a significant role in the mpg differences...

  6. #6

    Default

    i think air temp is the big factor here, in the summer its hot, plus you run A/C. winter its fairly cool/cold and you are on winter blend, ive seen the best mpg in mid to late fall, and again early late spring.

    Alex


    2011 GMC Sierra SLE 5.3 Z71 4X4 Stealth Gray Metallic / 2004 Chevy Impala LS 3.8 Cappuccino

    Tow mirrors - Diablew Tuned - Flowmaster Regular 40 - Ready Lift 2.5' lift - BFG LT A/T K/Os - Carr Light Wing - TruckLite LED lights - Optima Red Top - 50% Front Window Tint - Line-X bedliner - Airaid MIT - Tekonsha P2 - ARS Billet Grill - Fia custom fit seat covers

  7. #7

    Default

    Those observations match my own...

  8. #8
    Legend
    GMCErica's Avatar
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    Default

    I know that I dont have a pick up truck like everyone else does, but I noticed when I got my new exhaust, my fuel efficiency and economy went down. I don't use my air conditioner at all, as that uses up gas as well for me. But up here in the Great Canadian north, in the winter we plug in our trucks when it goes to -20 to -50C, or you wont start at all, and I notice my fuel efficiency is better in the winter when I cover my grille and plug her in. Normally, I get about 14 in the city 20 on the highway, combined about 17 or so. Just gotta watch the heavy foot with the exhaust, sounds so good though. I thought about CAI and scanners, but they don't do too much of anything... a few MPG or so, but not worth the extra 5 to me.



    2008 GMC ENVOY SLT
    GT RACERS Black Diamond Grille
    | PIAA Headlights| BEAMERS Pro HID Kit 6,000K Diamond White |
    3" LiftMeister Body Lift Kit
    |Skyjacker Suspension| MagnaFlow Exhaust w/tip |Hella Supertone Horns| Blacked out Body


    "Silly Boys! Lifted Trucks are for Girls"
    "If you can't beat 'em, then your going to slow" :sign0081:

  9. #9

    Default

    Quote Originally Posted by GMCErica View Post
    I noticed when I got my new exhaust, my fuel efficiency and economy went down.
    The I6 engine needs a little back-pressure to help the mpg, the new exhaust removed most of that back-pressure. It's not a bad thing, just a little hit in the mpg.

    Quote Originally Posted by GMCErica View Post
    But up here in the Great Canadian north, in the winter we plug in our trucks when it goes to -20 to -50C, or you wont start at all, and I notice my fuel efficiency is better in the winter when I cover my grille and plug her in.
    I switched to synthetic oil years ago for that reason. With the synthetic, it starts the same winter/summer without plugging it in.


    But.............a warm truck, just after you start it, can be a nice thing in the winter.

  10. #10
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    Quote Originally Posted by RayVoy View Post
    The I6 engine needs a little back-pressure to help the mpg, the new exhaust removed most of that back-pressure. It's not a bad thing, just a little hit in the mpg.

    I switched to synthetic oil years ago for that reason. With the synthetic, it starts the same winter/summer without plugging it in.




    But.............a warm truck, just after you start it, can be a nice thing in the winter.
    Yea, I figured that with the new exhaust, the Envoy mpg are tailored to the stock one, and I talked to all my mechanics, truck friends and really, not that big of a difference, instead of going a week without filling up, more like 5-6 days.. I have a heavier foot now, LOL I like to hear it.. You know all about cold too brrr... But the trucks love a plug in... And my leather seats arent as cold.. LOL

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