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My mileage sucks!!!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 89GMCSuburban, Jan 1, 2002.

  1. 89GMCSuburban

    89GMCSuburban 1/2 ton status

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    Lately, with tires maxed at 50 PSI, I've been getting about 12 MPG. It blows smoke on startup, if I'm idling for more than 1 minute and I hit the gas, it smokes, and if I stop very hard then tap the gas, it smokes. What's wrong with it??? It's got 188,000 miles. Where do I start? I run 10W40 Valvoline Max Life with Rislone engine treatment. Could it be my O2 sensor?

    Red 1989 GMC Suburban SLE V1500 - TBI 350, 700R4 w/ shift kit, Quad-shock front, 31/10.50/15 Pro Comp MT, 4.10 gears, Duals off cat
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I'd say with 188,000 miles you're rings are probably worn causing the smoke you're getting. The motor is still returning decent mileage though...12 ain't bad in a 3 ton Suburban.

    Rene

    <font color=green>Dyslexics of the world...UNTIE!</font color=green>
    <a target="_blank" href=http://coloradok5.com/gallery/project_T2> tRusty pics...</a>
     
  3. muddysub

    muddysub 1 ton suburban status Staff Member Moderator GMOTM Winner

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    my 89 sub has 152,000 on it and i think i get about 10-12mpg.

    LOOK OUT MOAB, HERE COMES THE SUB!!!!!
    scott,
    1989 GMC suburban 3/4t 4" lift rollin on 36" swampers, tbi350, th350, np241
     
  4. woody9

    woody9 1/2 ton status

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    My 91 can squeek out 14 on a good day.. (mostly down hill?).. 350/700R4/4:10s/16's..... and 165,000.
    Best it's got since i've owned it was a tick under 16 when i took it home to Colorado from San Antonio and i've never seen that since it left Texas!
    Traveler has posted a number of suggestions on this site
    http://pacific-audio.com/performance/discussion.html<P ID="edit"><FONT class="small">Edited by woody9 on 01/01/02 06:38 PM.</FONT></P>
     
  5. Chris Demartini

    Chris Demartini 1/2 ton status

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    <font color=blue>Please stop running your tires at 50 PSI. You're going to wear the center prematurely. Just run them at whatever the door plackard says, GM put it there for a reason. What color is the smoke (black = running rich, blue = oil)? How long ago was your last tune up? Where do you drive mostly (around town, flat highways, mountain roads)? Oh yeah 12 mpg isn't bad for a 6000 lb brick wall.
     
  6. DesertDueler

    DesertDueler 1/2 ton status

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    My 87 use to get 14 mpg. I dont know what happend, but now its only getting 7.5 mpg :( Its a 350 TBI, 700r4, 208, 3.42s and 33s.

    86Jimmy 4"&35"MTRs,87 burb 4"&33"MT,69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  7. Burbinator

    Burbinator 1/2 ton status

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    My '91 3/4 ton gets about 12-14 mpg on average, with 140K on the ticker. I agree with tRustyK5 that you more than likely have worn rings.

    The learning curve is a toll road...ride with someone who has already paid!
    <a target="_blank" href=http://community.webshots.com/user/abshort>U.S.S. Nimitz II</a>
     
  8. 79ChevySB

    79ChevySB 1/2 ton status

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    Your Valve guides in your heads could be worn. I had a Camaro that would smoke (Blue smoke) when I fired it up and it was the valve guides. Good luck.

    Hey this is FUN!
     
  9. HarryH3

    HarryH3 1 ton status Author

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    12 ain't that bad for a Sub. My wifes '94 gets 10 in town and 14 on the highway. It just takes a lot of fuel to move one of these monsters around! I try not to think about what kind of mileage my '90 will get once I drop in the 454. [​IMG]

    <font color=black>HarryH3 - '75 K5</font color=black>
    <a target="_blank" href=http://www.angelfire.com/super/ThunderTruck>www.angelfire.com/super/ThunderTruck</a>
    It's a great day to be alive...
     
  10. hammer

    hammer 1/2 ton status

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    7 that's all I have been getting but there is alot of idle time 129 miles 18.3 gallons and it's 13 highway miles to work everyday

    <font color=red>Let me at it I can break it</font color=red>
     
  11. Twiz

    Twiz 1/2 ton status

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    Blue smoke on excell = Rings
    Blue smoke on decell = Valve guides
    Blue smoke on start-up = Valve stem seals or Valve guides

    From the discription, kinda sounds like the oil is seeping in past the valves to me. But with 188 thousand miles on it, it would need to be reringed and valves worked. If you try to reseal the top, the bottum will blow out of it. The engine is worn as a assembly, fix the top, it will add pressure to the lower end, and blow the rings.

    12 MPG doesn't sound to bad to me, considering 188,000 miles on the engine. Count your blessings, and start saveing your money for a crate engine from a good sorce, like a G.M. crate engine. You could be into one of those for about (guessing) $2500 plus install.

    Take it easy on the gas pedal and you should be O.K. for awhile.

    <font color=blue>Wow Factor
    A SBC at 6000 RPM, Piston speed of 60 MPH.
    3- The intake charge reaches a speed 4 X greater than the piston.
    Thats 240 MPH.
     
  12. Burbinator

    Burbinator 1/2 ton status

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    The black and blue smoke have been covered...white smoke = coolant and a blown head gasket(s) and ultimately failure of the cat, among other things. The color of the smoke is key to diagnosing where to concentrate repair efforts.

    Haze gray and underway...<font color=blue>or blue, in my case.</font color=blue>
    <a target="_blank" href=http://community.webshots.com/album/26246038MbQsYWKcbo>U.S.S. Nimitz II</a>
     
  13. 78yellowchev

    78yellowchev Registered Member

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    you should be thankful my 78 gets 6 mpg but i do alot of city driving
     

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