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Silverado 5.3 Gas Mileage

Discussion in 'General Chevy & GM Tech Questions' started by Chad513, Sep 14, 2012.

  1. Chad513

    Chad513 Rockstar 100 Posts

    I just dropped a 5.3L engine into my Silverado and I'm shocked at the gas mileage I'm getting now. I get like 17-18 mpg while going 80. Is that normal? I have an intake, exhaust and bully dog programmer. My 4.8L that was originally in the truck was getting like 25 so I don't understand why it would be that big of a drop. I was just wondering if that was the normal mileage for you guys out there with the 5.3. Please help!
    btw the engine was out of an 04 Silverado. and I have 3.23 gears in the rear end.
    Last edited: Sep 14, 2012
  2. sfdefender24

    sfdefender24 Rockstar 4 Years ROTM Winner 100 Posts

    Well its a lil bigger motor with a lil more power, which will result in a drop of mpg and also going 80 with that motor means it needs more fuel which also results in lower mpg. so that is about normal.
  3. Chad513

    Chad513 Rockstar 100 Posts

    It scares me lol. I have never seen that low of a number. Your truck is sick btw man. I just joined the Navy and am hoping to do lots of stuff to my truck when I go on leave.
  4. Jeremy09LTZCrew

    Jeremy09LTZCrew Epic Member 5+ Years 1000 Posts

    I can squeeze 20-21 assuming a flat highway doing 60-65. After 65 it starts dipping fast. 17-18 at 80 doesn't surprise me at all and sounds about right. I've toyed with the idea of dropping a 6.2 into mine at some point. I most likely won't, but if I did I'd expect a 10-20% drop in highway mpg just like you noticed going to the 5.3.
  5. sfdefender24

    sfdefender24 Rockstar 4 Years ROTM Winner 100 Posts

    chad- thanks man. its all deployment in that truck lol.
    jeremy- i thought about a 6.2 as well, once its paid off i think i might hop up to it for the extra power.
  6. 2k8z71

    2k8z71 Rockstar 100 Posts

    Chad: what rate did you get in the Navy? I was in the Navy myself. Also, I used to get 22-23mpg driving from Bakersfield Ca to Los Angeles, then I leveled my truck and bigger rims/tires and now i get 19 if I do it right lol. All I have is an intake (the mileage was done via the good ole math method instead of DIC)
  7. CorvetteOJ

    CorvetteOJ New Member

    I have a '12 Ext Cab with 5.3 and 3.08 gears, a PCM for Less tune, K&N system, magnaflow single in, dual out and 20s on the ground. The absolute best mpg I can get on the highway, running an average of 80 mph, is 15mpg. It would be a miracle to get 18mpg at 80, in my opinion. BTW, I'm retired Air Force myself.
  8. sfdefender24

    sfdefender24 Rockstar 4 Years ROTM Winner 100 Posts

    corvetteOJ your best bet to help get milage up is new gears. having 3.08 with a 5.3 is causing you to run at a higher RPM which is killing your mpg and having 20s which are heavier is also killing it.. i had 3.42s when mine was stock and average just over 20mpg on the highway. but now that mine is lifted im soon to be running 4.56s...Also what did you do in the AF, im currently enlisted. just hit my 3 year mark in july and am on my 2nd deployment.
  9. CorvetteOJ

    CorvetteOJ New Member

    Thanks man, I appreciate the advice but would rather not start messing with the rear gears while it is still so new (three months old). I agree 100%! I was a little disappointed when I discovered it had 3.08s. Everything else on the truck was exactly like I wanted and I was in a position where I needed/wanted to trade "overnight" so to speak, so I did.

    I did 27 years in the Air Force, enlisted, retired CMSgt. The first half of my career (approx. 14 years) I was a crew chief on fighters, mostly F-4s. The second half (13 years) I was in PME, (Professional Military Education) at various positions, including Commandant for three years.
  10. sfdefender24

    sfdefender24 Rockstar 4 Years ROTM Winner 100 Posts

    Your welcome man, Im shocked and dissapointed to see chevy is putting 3.08s in trucks now. Makes no sense to me personally. And you are correct with it being so new, i wouldnt wanna mess with the set up just yet. Sounds like you did some major time, thanks for your service. Glad to see alot of active and prior military on here.

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