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  1. #1

    Default MPG decrease with OLM decrease. Any one else notice this?

    I noticed over my last two oil changes that when the oil life monitor gets down around 25% my mpg begins to decrease. From averaging 17.4 in the city to around 16.4. On the highway it drops from 21 to 18mpg. I changed my oil today (olm at 30%, I changed it because I wanted to see if mpg increased like last time) and my mpg went back up to 17.5mpg city and 22mpg highway. I use Mobile 1 5w-30 high millage oil and ac delco pf 46 filters. Yes, the oil does look dirty when it comes out. The millage is from the DIC and hand calculated. I don't think that the oil would be broken down that much considering that the OLM is set for conventional not synthetic. But, I have noticed the change over the last 2 oil changes. When I change it, it goes up instantly. Any ideas? Anyone else notice this trend?

    1995 Silverado 4x4
    6" BDS Suspension Lift-3" Body Lift-Add A Leaf in rear -Trailmaster SSV Shocks-Duel Steering Stabilizer Kit -AirAid Cold air intake-
    4.56 Gears with Detroit Auburn Locker-Pro-Comp Traction Bars with duel shocks-Aluminum Skid Plate Kit-38.5" x 16.5" Mickey Thompson Baja Claws-Constant Dropping fuel gauge

    2005 Yukon XL Jet Power Programmer, Bilstein Shocks, Bilstein rear springs, Helwig Anti-sway bars, EGR Window Visors, EGR Hood Shield, Denali Headlights, Headlight harness upgrade, GE NightHawk Bulbs, White Night Rear lighting system, Russell Braided SS brake lines, PowerStop Brake pads, PowerStop cross drilled and Slotted Rotors, http://www.gmtruckclub.com/forum/sho...5-GMC-Yukon-XL
    2002 Silverado ext cab 2wd (Sold)
    2003 Yukon XL (Totaled)

  2. #2
    Jr. Engineer BRB46's Avatar
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    Default

    That's quite interesting. I haven't noticed that but wasn't looking either. I am at 83% now and will monitor it as it gets lower. Will report my findings later.
    2006 Silverado 1500 5.3L ecsb Z71,afe pro s dry air filter, color matched tailgate handle and bezel,color matched front bow tie, led interior illumination, 5000K HID lows, Black powder coated wheels, Blacked out body side moldings, Rough Country 2.5" level/lift kit, Magnaflow muffler

  3. #3

    Default

    Quote Originally Posted by BRB46 View Post
    That's quite interesting. I haven't noticed that but wasn't looking either. I am at 83% now and will monitor it as it gets lower. Will report my findings later.
    Thanks! I am just interested to see if others notice the same thing. Like I said around 30%-25% I notice the loss in mpg. What oil are you using?

    1995 Silverado 4x4
    6" BDS Suspension Lift-3" Body Lift-Add A Leaf in rear -Trailmaster SSV Shocks-Duel Steering Stabilizer Kit -AirAid Cold air intake-
    4.56 Gears with Detroit Auburn Locker-Pro-Comp Traction Bars with duel shocks-Aluminum Skid Plate Kit-38.5" x 16.5" Mickey Thompson Baja Claws-Constant Dropping fuel gauge

    2005 Yukon XL Jet Power Programmer, Bilstein Shocks, Bilstein rear springs, Helwig Anti-sway bars, EGR Window Visors, EGR Hood Shield, Denali Headlights, Headlight harness upgrade, GE NightHawk Bulbs, White Night Rear lighting system, Russell Braided SS brake lines, PowerStop Brake pads, PowerStop cross drilled and Slotted Rotors, http://www.gmtruckclub.com/forum/sho...5-GMC-Yukon-XL
    2002 Silverado ext cab 2wd (Sold)
    2003 Yukon XL (Totaled)

  4. #4
    Jr. Engineer BRB46's Avatar
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    Apr 2011
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    Western Mass
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    I use Pennzoil Platinum 5W30 full synthetic. I had previously used Mobile 1 but for some reason i had to add a quart every 2500 miles. Now I add one every 5500 or so.
    2006 Silverado 1500 5.3L ecsb Z71,afe pro s dry air filter, color matched tailgate handle and bezel,color matched front bow tie, led interior illumination, 5000K HID lows, Black powder coated wheels, Blacked out body side moldings, Rough Country 2.5" level/lift kit, Magnaflow muffler

  5. #5
    Sr. Engineer
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    Default

    Not intending to hi jack the thread but.... I change my oil when the DIC says it's time and that is normally around 5,800 to 6,500 miles. So the question is ; What is this Oil Life Monitor you all speak of and does my 2000 Yukon have it? How does one access it?
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  6. #6
    Jr. Engineer BRB46's Avatar
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    It is part of your DIC. Mine shows oil life in %, hence the life of the oil. I keep track of the mileage with my tripometer A. It starts at 100% and as you drive the % drops based on driving habits and outside air temp I believe has an effect on it as well. In the summer months I can go 8000 miles before it hits zero percent. In the colder months 5500 is all it gets.
    2006 Silverado 1500 5.3L ecsb Z71,afe pro s dry air filter, color matched tailgate handle and bezel,color matched front bow tie, led interior illumination, 5000K HID lows, Black powder coated wheels, Blacked out body side moldings, Rough Country 2.5" level/lift kit, Magnaflow muffler

  7. #7

    Default

    Quote Originally Posted by BRB46 View Post
    It is part of your DIC. Mine shows oil life in %, hence the life of the oil. I keep track of the mileage with my tripometer A. It starts at 100% and as you drive the % drops based on driving habits and outside air temp I believe has an effect on it as well. In the summer months I can go 8000 miles before it hits zero percent. In the colder months 5500 is all it gets.
    Mine is the same and I do the same thing as described above. My 2002 just had a light that would come on and say change oil, no percentage.

    1995 Silverado 4x4
    6" BDS Suspension Lift-3" Body Lift-Add A Leaf in rear -Trailmaster SSV Shocks-Duel Steering Stabilizer Kit -AirAid Cold air intake-
    4.56 Gears with Detroit Auburn Locker-Pro-Comp Traction Bars with duel shocks-Aluminum Skid Plate Kit-38.5" x 16.5" Mickey Thompson Baja Claws-Constant Dropping fuel gauge

    2005 Yukon XL Jet Power Programmer, Bilstein Shocks, Bilstein rear springs, Helwig Anti-sway bars, EGR Window Visors, EGR Hood Shield, Denali Headlights, Headlight harness upgrade, GE NightHawk Bulbs, White Night Rear lighting system, Russell Braided SS brake lines, PowerStop Brake pads, PowerStop cross drilled and Slotted Rotors, http://www.gmtruckclub.com/forum/sho...5-GMC-Yukon-XL
    2002 Silverado ext cab 2wd (Sold)
    2003 Yukon XL (Totaled)

  8. #8

    Default

    Pikey, you are a great addition to this forum, and you really have me stumped here. There is nothing in the breakdown of lubricity or viscosity that could have that much impact on your MPG. Obviously, as oil gets dirty and thickens, it loses some of it's lubricity, which creates a bit more friction (or "drag") on internal components. But, I think we are talking about an effect well below 1/10 of a mpg, versus one or two full mpg. What I would rather suspect is that the bypass of dirty oil through the pcv and back into the intake may affect combustion, hence MPG. As the oil gets older/dirtier/contaminated, it is still passed back through the intake. Even clean oil injected into a fuel mixture reduces octane, and dirty oil would be that much worse. Only reason I can think of. Does this make any sense?
    Las Vegas, NV...2001 Silverado 1500 LT Z71 Stepside X-cab, 171,000 miles, 5.3, cat-back duals, leveling kit, 3.73, 17" rims, more to come...

  9. #9

    Default

    Pikey, you are a great addition to this forum, and you really have me stumped here.
    Thank you for the compliment.
    that does make sense. I am considering making a catch can. I think that for under $25 I can get a high quality watts filter
    Last edited by Pikey; 01-03-2014 at 04:55 PM.

    1995 Silverado 4x4
    6" BDS Suspension Lift-3" Body Lift-Add A Leaf in rear -Trailmaster SSV Shocks-Duel Steering Stabilizer Kit -AirAid Cold air intake-
    4.56 Gears with Detroit Auburn Locker-Pro-Comp Traction Bars with duel shocks-Aluminum Skid Plate Kit-38.5" x 16.5" Mickey Thompson Baja Claws-Constant Dropping fuel gauge

    2005 Yukon XL Jet Power Programmer, Bilstein Shocks, Bilstein rear springs, Helwig Anti-sway bars, EGR Window Visors, EGR Hood Shield, Denali Headlights, Headlight harness upgrade, GE NightHawk Bulbs, White Night Rear lighting system, Russell Braided SS brake lines, PowerStop Brake pads, PowerStop cross drilled and Slotted Rotors, http://www.gmtruckclub.com/forum/sho...5-GMC-Yukon-XL
    2002 Silverado ext cab 2wd (Sold)
    2003 Yukon XL (Totaled)

  10. #10

    Default

    Mike....just as the other Member's have mentioned, that's interesting......

    MIKE


    99"SILVERADO
    5.3 l 3.73 l G80
    BLACK BEAR CUSTOM TUNE
    SNUGTOP l COLORMATCH l KATZKIN










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