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  1. #1

    Default Dealeship oil change equals less MPG and power GRR!

    Had my 100K mile oil change a week ago. Besides trying to sell me $700 service package I have a strange problem. ($200 parts rest labor [IMG]My truck always runs 40 PSi at highway speeds and gets 18-20 MPG (non SS 5.3 2003 ext)

    Now at freeway speeds Im nearing 50 psi and 15-16 MPG No other change was made and the shift started the moment I left dealer.... No SES light same gas as always and a few tanks ran through...

    I questioned dealer and they said I need that $700 service to fix? Im thinking they used some thick oil and thought they were screwing someone that wouldnt put 2 and 2 together...

  2. #2

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    Sounds like the wrong oil put in to me and the $700.00 service fix--- scam!

  3. #3
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    Welcome to the GM truck club Lowbucks.. I agree on the heavier oil scenario, although just having "new" oil can have an effect on your oil pressure & cause it to go up a bit. Maybe 3 or 4psi, but not 10, unless you had 5-30wt in it & the shop put 50-60 wt. in.
    You might want to check your tire pressures as the shop could have aired them down & if you generally run them higher, that could be adding to your lower mpg.

    Just as a precaution, pull the dipstick & smell it. Does it smell like "gear" oil? Most shops have automatic overhead oilers & if the mech was sleepwalking, he could have grabbed the 85-90 wt gear oil gun by mistake & given you 5 quarts of that.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  4. #4

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    Quote Originally Posted by stephan View Post

    Just as a precaution, pull the dipstick & smell it. Does it smell like "gear" oil? Most shops have automatic overhead oilers & if the mech was sleepwalking, he could have grabbed the 85-90 wt gear oil gun by mistake & given you 5 quarts of that.
    Oh god I hope its not gear lube... I do run higher air pressure maybe they did run em down to 35... Will check tomorrow...

  5. #5
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    I'm not saying it is, BUT If it's gear oil, have it towed back to the dealership (don't drive it) Take the dipstick & wipe it on the service managers nose. They are responsible for new oil & filter & the tow bill, & any further complications to your engine. Just be sure & get everything documented in case your engine develops problems associated with this..
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  6. #6
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    Default

    I've heard that modern vehicles have some sort of learning curve after the battery is disconnected, and it takes a tank or so to get best mpg after the battery is reconnected!!??
    Hard to believe it could unlearn 4 mpg!!?? Besides you have run a few tanks thru.

    I switched my 1998 Suburban to Mobil 1 10w30 from Mobil 1 5w30. I couldn't detect ANY change in MPG, so I don't think any actual oil change could cost you 4 mpg.
    Now diff lube- yeah-that could drop your mpg like a stone!

    If it is diff lube-like Stephan suggestsgbv yhgb -sniff it- it will have that nasty sulfur stench!! It will also really adhere to the stick. Plenty will be on the stick,and when you hold it upright or straight down it will take forever to drop and fall off the stick.

    I don't know if those shops have 20w50 oil in the overhead lines-maybe 20w50 could cost 2-3 mpg??

    Your 2003 should get pretty decent HY mpg-at 65 mph a 4x4 5.3 should get 18 mpg-no problem. My 1998 Suburban 5.3 2wd will get 18-19 mpg at 65 mph-the 5.3 is 1 mpg better-and by 2008 with cyl shutdown it is 2-3 mpg better.

    I would guess dropping air pressure from 50 psi to 35 psi would cost you .5 mpg or so mpg.
    Let us know
    CHARLIE
    1998 suburban-
    1/2 ton

    199500 miles
    River
    Ridge,LA

  7. #7

    Default

    IF it is gear oil the FIRST thing he should do is to make sure you have TWO INDEPENDENT good auto shops DOCUMENT in writing that it is gear oil. When he tows it into the dealership they are going to change it and then say it never happened and not put anything in writing. They aren't going to say they made a mistake and are going to do anything they can to get out of any liability if there is vehicle damage.


    Quote Originally Posted by stephan View Post
    I'm not saying it is, BUT If it's gear oil, have it towed back to the dealership (don't drive it) Take the dipstick & wipe it on the service managers nose. They are responsible for new oil & filter & the tow bill, & any further complications to your engine. Just be sure & get everything documented in case your engine develops problems associated with this..
    2010 GMC Savana AWD
    Silver Metallic, 5.3L, 3.73 Gears and G80 Heavy Duty Locking Rear Differential, American Racing Off Road Series ATX Chrome Assaults 17X8, BFG T/A KO's 245/70/17 (Stock Size).
    Alpine ida-x303 head unit, Alpine Power Pack, Alpine SPS-600 Speakers
    Viper 350HV car Alarm
    Coverking Neoprene Seat Covers
    42" Slider Windows
    Custom Bed with 6" Memory Foam Mattress
    Avery Berber Carpet



  8. #8

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    Well its not gear lube. Its nice clean oil color but doesnt run down the stick(Diesel fleet oil 20/50 maybe). Reminds me of Motor Honey (AKA bearings in a can)
    AlsO they dropped my tire pressure down from 45 to 32. I will stick with the oil for remainder of the 3000 miles then swap in some 5/30 royal purple and a KN filter. I run that in my Hotrod with good results..

  9. #9

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    perfect example of why I will never take one of my vehicles to the stealership, aside from warranty work
    Justin
    1990 Silverado Stepside



    2003 Olds Alero-
    64,XXX

  10. #10
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    Quote Originally Posted by Lowbuckx View Post
    Well its not gear lube. Its nice clean oil color but doesnt run down the stick(Diesel fleet oil 20/50 maybe). Reminds me of Motor Honey (AKA bearings in a can)
    AlsO they dropped my tire pressure down from 45 to 32. I will stick with the oil for remainder of the 3000 miles then swap in some 5/30 royal purple and a KN filter. I run that in my Hotrod with good results..
    Ha ha ha "bearings in a can" I've never heard that before. I'm glad it's not gear oil. It's possible the 13 lb drop in tire pressure (X 4) could be causing some of the engine laboring you're noticeing too. Definitely some mpg loss.
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


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