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  1. #1
    Sr. Apprentice
    Join Date
    Jul 2009
    Weatherford, TX

    Default Gas Mileage Woes [Expired Topic]

    Hi y'all. I've only been on here a few days, and I'm loving the forum. After reading countless threads about many different issues, I'm beginning to think I'm not getting the mpg I should be getting with 2 of my 3 suburbans. The info is in my signature, but I'll give more detail here:


    1995, 350 TBI, K1500, 265/70-16 Tires, 140,000 miles
    It has great jump torque off the line and runs great after 2500RPM, but VERY sluggish between 1500-2500RPM. Only had it a few months, haven't checked anything on it yet....just realized I'm only getting 11-12, even on the highway. I added a tornado and K&N filter, but no help. Another note, heat gauge never gets anywhere near 210 unless I'm pulling a trailer. I'm thinking possibly someone put in a HighPerf chip and low-temp stat? Or maybe therm went out and they just didn't replace it at all? Your thoughts?????


    1989, 350 TBI, C1500, 31x10.5-15 Tires, 200+K miles
    This truck runs GREAT, but I can't seem to get over 13, even on the highway. I've had it about a year and a half, and it seems everyone else here is getting better mileage out of similar truck.

    So.....either 90% of you guys are lying about your gas mileageor my trucks need help.

    Thanks in advance!!!!
    '95 1/2 ton Suburban 4wd 350, 140K, w/ tornado and k&n filter | everything else stock

    '89 1/2 ton Suburban 2wd 350, 200+K, completely stock except 31 x10.50 tires & 40 series flowmaster

    '85 1/2 ton Suburban 2wd 350, 250+K, burnt valve :lol: , edelbrock 50 carb, comp cam, silvolite pistons, HiPerf distributor, 18" glasspacks

  2. #2

    Join Date
    Feb 2008
    Red Wing, Minnesota, United States


    Find out what gears you are running or what are your RPMs when you are at 60mph?
    99 K1500 Suburban LT "THE BEAST"
    Hypertech III, K&N, true dual

  3. #3
    Sr. Apprentice Bikeman's Avatar
    Join Date
    Apr 2009
    Charlotte NC


    I only get 13 on the hwy, 12 city though mine is a 2500

  4. #4


    My 99 with a 5.7 will get easily 18-20 on the highway (depending upon terrain). Only things I have ever done to accomplish are as follows:

    • Delco Plugs gapped at .40
    • Premium Plug Wires
    • Regularly change distributor cap and rotor (once a year)
    • Tire pressure at 35 pounds always.
    • Got rid of factory muffler for free flowing system
    • I always use cruise control on highway
    • And even though we have 75 mph speed limits I still run 65 on the Interstate. Start going above 65 and the mileage goes to hell in a hurry


  5. #5


    My '91 was somewhere around 13mpg.

    My '98 is somewhere between 16 and 17mpg.

  6. #6

    Cool Gas Mileage Woes

    Cooler thermastats will kill your gas mileage. Run what factory recommends. Also I agree with Evilnetwork keep it under 65 or under 2,000 rpms.

  7. #7

    Join Date
    Jun 2006
    River Ridge Louisiana-4 miles W of New Orleans-didn't flood-water stopped 800 yards away.


    My 1998 2wd 1500 Suburban gets 21 mpg on the 3000 mile trip from New Orleans to Flagstaff AZ and back.
    Of course, I keep my speed down-set the CC to 68 mph, and with all the road work and cities with 45/55 mph limits., I'm probably averaging just 62mph or so.
    Like others have said-speed kills mpg with a blocky vehicle like the Suburban.

    It is dead stock with 210,00 miles-syn oil and syn lube in diff- 42 psi tires- use the CC all the time.

    Your 1995 TBI should do better than 12-13 on the highway.Did it come with those 16" wheels" ? What sort of rpms do you turn at 60 mph? Don't waste your money on chips/CAI ETC. It is really hard to beat the OEM engineers for FE. No codes on the 1995- O2 sensors good etc?No check engine?

    You should be able to get 15 mpg at 70 mph with the 1995.
    1998 suburban-
    1/2 ton

    199500 miles

  8. #8


    Evil's tuneup advice is good. Also, take a look at this thread.

    I had huge improvements in power, and FE increased also. Plus, the TBIs are notorious for the TB to intake gasket cracking and leaking. Another thing to consider with the age/mileage of the vehicle is O2 sensors. As they get older and more use, they can become "lazy" with feedback which will affect performance and FE. The tire size on the sub is OK, although 245/75 would have slightly less drag. The 31's on the 89 are probably a big factor on FE too.
    When you hear hoofbeats, look for horses not zebras.

  9. #9

    dwill3015's Avatar
    Join Date
    Jan 2007
    Yacolt, Washington
    Blog Entries


    All good reccomendations. On my 87 K5 blazer w/5.7 TBI I installed a Helix TB spacer, Hypertec performance chip, and flipped the lid of my aircleaner over and performance gains and throttle response were like night and day. With the added performance came better fuel mileage as well.
    Washington State
    2006 Silverado 2500HD LT3 4X4 CC SB Duramax LBZ
    Tuff Country 6" lift, 35" Toyo M/T's on 20" Ultra Peacemaker wheels, Quadzilla Stealth2 programmer, Diamond Eye 5" cat-back exhaust, factory Special order color Yellow.

  10. #10
    Legend unplugged's Avatar
    Join Date
    Sep 2006
    High Deserts of SoCal


    I haven't checked my mpg's in over a year. The last time I did it was 11mpg. My mileage sucks and I don't care. I don't drive it for its miles per gallon. I drive it cuz it hauls a lot of people, cargo, and it tows the pwc without any sweat. The only thing "green" about my burb is the paint!
    There is no way to happiness....happiness is the way.:yipi:  _vXMYypuKMJFw671uF2ZPhjez_j-atRmcjM2zQKpQi1JSsB75/burb1.JPG
    High Desert SoCal
    93 K1500 burb (personal) 350 AT 3" Lift 250K+
    02 Honda Civic LX
    Looking for a 1990's Miata for an engine swap

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