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Thread: Fuel mileage ??

  1. #1

    Default Fuel mileage ??

    I recently purchased a 2WD 99 C1500 Suburban with a 5.7L, 4L60e, and 3.73 rears. It has about 137,000 on it and it appears to be very well maintained. The previous owner told me that it pretty much gets 14 hwy or city. I figured it should have got a little better on the highway. Some friends of mine are claiming high as 19 in theirs.

    A recent family vacation from east Texas to the Florida panhandle proved the horribly consistent 14 mpg. I actually got as high as 14.2. While in Florida, it developed a very hard 1-2 shift and the CEL came on. When I got back to Texas, I hooked my scanner up and got a P1870 I think it was. Anyways, wound up putting a reman valve body in and now everything is shifting fine, torque converter locking up and it cruises 70 at 2000 rpms. I haven't got to drive it enough to determine the mpg's yet. About how bad does the torque converter not locking up affect the mpg?

  2. #2

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    14 mpg is kind of low. I get 15mpg on the highway in my K1500 and about 12 in the city. I think you should be getting upwards of around 20mpg highway with your ride.

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    Depending on what you had in it for a load, along with speed etc.. 15 is really all they get with the 5.7L they will get a bit more but most people average around that kind of milage, however the torque converter not locking is usually good for around 2mpg in the burbs.
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  4. #4

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    I figured the tc lockup would have a pretty good impact on it. 2 mpg more? I'll take it!

    The idle is a little unstable so I think I'll check the plugs and give the injectors a good cleaning. See if that'll help any.

  5. #5

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    I can't tell you much, but I'm getting 14 in my '89 4wd 5.7 suburban, so I suspect yours is a bit low.

    Driving habits make a difference, of course, I probably average a good 1mpg plus extra in mine just because I barely touch the brakes (takes some long range attention!), accelerate nice and easy, and don't push 70mph.
    Christof
    1989 GMC Suburban
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    Homeschooler, shooter, VFW, Desert Rat.

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    Quote Originally Posted by Treadnmud View Post
    I figured the tc lockup would have a pretty good impact on it. 2 mpg more? I'll take it!

    The idle is a little unstable so I think I'll check the plugs and give the injectors a good cleaning. See if that'll help any.
    I would also take a VERY close look at the cap and rotor. the 5.7L vortec is known for issues with them. And 15-16 is about the best my buddy gets with his 2000 burb exact same model as yours (almost the same color lol)

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    when chevy switched to the vortec 5.7 from the old tbi 5.7 the fuel economy took a hit, my parents had a 92 K1500 and we pulled 20mpg (70 MPH too)on a trip to texas (from MN)and carrying five people and their gear for a 2 week trip. I bought my 99 K1500 and have NEVER pulled more then 16mpg, and i have done everything I can to try and get better MPG. But for a 2wd you should be getting atleast 16 MPG on the hwy and about 13 in town
    99 K1500 Suburban LT "THE BEAST"
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  8. #8

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    Quote Originally Posted by murdog94

    I would also take a VERY close look at the cap and rotor. the 5.7L vortec is known for issues with them. And 15-16 is about the best my buddy gets with his 2000 burb exact same model as yours (almost the same color lol)
    I'll do that. Thanks. Any recommendation on the brand or style of rotor? Such as brass or aluminum contacts?

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    Nope since they both corrode quickly it is a minor defect with the Vortec motors.

  10. #10

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    Quote Originally Posted by vncj96
    when chevy switched to the vortec 5.7 from the old tbi 5.7 the fuel economy took a hit, my parents had a 92 K1500 and we pulled 20mpg (70 MPH too)on a trip to texas (from MN)and carrying five people and their gear for a 2 week trip. I bought my 99 K1500 and have NEVER pulled more then 16mpg, and i have done everything I can to try and get better MPG. But for a 2wd you should be getting atleast 16 MPG on the hwy and about 13 in town
    Well, before the valve body job, this burb averaged a very consistent 14 mpg whether in city or highway across 40 gallons of 87 octane. I don't suppose running a better grade fuel would help in the long run.

    ---------- Post added at 10:42 AM ---------- Previous post was at 10:36 AM ----------

    I did check the plugs. I am guessing these are the IR plugs everyone is talking about. They are are AC brand, however, the contacts on the electrode appears to have a bunch of tiny bumps on it. Strange.... Never seen anything like this, but then again I'm a diesel mechanic! Ha! 😃🚚

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