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post #1 of (permalink) Old 01-05-2017, 07:36 PM Thread Starter
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Gas mileage

Hey guys,

Just wondering what kind of gas mileage are you getting in your 8th gens? With stock tune? And if you're running top tier gas? And any other considerations like excessive oil consumption (some cars seem to really drink the oil through the PCV and back through the intake and some don't at all thus don't experience the carbon issues and reduced gas mileage like other do). Also if you mostly if you do city or highway driving. I'm getting about 16 town 20 highway top tier 93 octane which is up a few miles after replacing the evap purge solenoid and the canister vent solenoid which were both bad. Mine drinks a lot of oil and I'm wondering if my mileage has decreased enough that I can get the dealer to do a manual cleaning of the valves under the powertrain warranty. The normal $100 deposit won't cover them telling you whether or not it will, so I'm fishing for evidence. Thanks!
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post #2 of (permalink) Old 01-05-2017, 08:17 PM
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2013 Impala, 3.6L, stock tune, 89 octane (just because, I know it does me no good to use it on a stock tune). The in-dash display reads 25.5mpg right now, with a decent mix between city/highway. I drive 15 miles one way to work and 10 of that is straight highway. If I'm 100% highway, anywhere from 32 to 36 MPG at 65mph.

Depending on how heavy of a foot you have, you should be able to get more MPG than you are seeing right now.


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post #3 of (permalink) Old 01-05-2017, 11:10 PM
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Garage
I also have a 2013 with the 3.6 and a stock tune. I use exclusively top tier fuel 87 octane. I tried 93 once and saw zero change so deemed it unnecessary. I get about 28 mpg on the highway at 77-78 mph. Around 70 I'll see 29-30 mpg. City... I'm liberal with the throttle once it's warmed up so that number isn't particularly pertinent, but on my commute which was 7 mile highway and 6 city, I'd average around 22 mpg. Over the course of an 650 mile week with 550 of those miles as highway running up to 85 mph, I saw 24.5 mpg.

Car has 70k on the clock, full synthetic oil changes since 20k, and in the 50k miles I've owned it, easily 40k of them were highway, if not more.
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post #4 of (permalink) Old 01-06-2017, 05:18 AM
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I had a 2008 with the 3.5L. I would average around 26.5mpg. Most of my driving to work is 55mph back roads with a few stop signs. I would get 30-33mpg on the highway doing around 78mph. Running 87 gas, top tier when possible, but not always.
I now have a 2013 with the 3.6. Average around 25.5mpg going to work. 28-30 mph on the highway doing 78mph. Run 87 gas, almost always top tier.
Seems like there is still something wrong with your vehicle. Even when I am very heavy on the throttle in my car, I've never averaged less than 23mpg for a tank.
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post #5 of (permalink) Old 01-06-2017, 05:34 AM
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I use 93 octane (Mostly non-TopTier now since I work from home now and there are no TopTier stations around my home) and I average about 22mpg - mostly 35-45mph country roads with very little highway driving. I have VERY little oil consumption and VERY little oil in my intake tube when I check it. I honestly think that the more "aggressive" that you drive, the more oil will end up in the intake due to increased vacuum because of heavy throttle. No evidence to support that - just makes sense to me.

50k miles on my 2012 LT - purchased with 19k miles. Engine power and gas mileage are the same as when I bought the car.

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post #6 of (permalink) Old 01-06-2017, 08:18 AM
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25 to 27 mpg. to/from work. 12 mile county rd, 7 miles of city, 24 of highway at 65 to 75mph depending on how I feel.. moderate to heavy throttle foot when warmed up. stock tune.
30.9 top recorded mpg on a 360 mile stretch between stations running 75mph near constant from home to valdosta ga. No noted oil consumption. have not checked the intake tube. running Valvoline syn blend for high mileage engines. at 89600 miles right now. purchased at 84k miles. last oil change got me almost 6 qts out of the pan.

lets not forget remote start usage. I use mine when there is frost on the windows, usually 3 to 10 minutes three times a week. maybe five times total if I don't lay over on my route and have to defrost again at night while I do paperwork. (18 wheel driver)

also, remote start is a great way to be able to check for cold start rattle and other noises.
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post #7 of (permalink) Old 01-06-2017, 08:38 AM
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Good point - I remote start my car a LOT! :-) When it's cold out, I'll let it sit there running for about 10 minutes to warm up. It definitely brings the MGP down!

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post #8 of (permalink) Old 01-06-2017, 09:09 AM
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Completely stock, captured via Automatic:


This week so far: 21.0
Last week: 24.7
Week of Dec 19: 24.1
Week of Dec 12: 22.9
Week of Dec 5: 19.8 (that was an e85 fill up)
Week of Nov 28: 20.4
Week of Nov 21: 24.9
Week of Nov 14: 20.5
Week of Nov 7: 24.2
Week of Oct 31: 24.4

- Ryan Mercer
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post #9 of (permalink) Old 01-06-2017, 09:22 AM
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Originally Posted by ryanmercer View Post
Week of Dec 5: 19.8 (that was an e85 fill up)

Are these not complete fill ups from empty? Compared to your other MPG...looks like you should use e85 way more often, as it does not seem to affect your gas mileage very much at all. It would make more sense if you were only putting in a couple of gallons of e85 though.
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post #10 of (permalink) Old 01-06-2017, 09:34 AM
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Quote:
Originally Posted by reubenswinks View Post
Are these not complete fill ups from empty? Compared to your other MPG...looks like you should use e85 way more often, as it does not seem to affect your gas mileage very much at all. It would make more sense if you were only putting in a couple of gallons of e85 though.
Fill up from empty, no. I use about half a tank of gas a week and fill up every Sunday. Sometimes e85 is freakishly cheaper at the Thortons I fill up at, when it is I'll usually fill up with it.

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post #11 of (permalink) Old 01-06-2017, 01:20 PM
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Garage
2010 3.5 on stock tune running whatever fuel i'm near when i decide to fill up on 87 octane gets 14-16 in strictly city. this past week running the country roads of michigan i was getting 25/26 of non fuel efficient driving. on the highway i see 28-34 depending on the trip and weather conditions. i will note this winter gas this year seems to be killing mileage worse than normal....or maybe it's me/weather again...

i will note the local shop told me i have a leaky rear main seal....and i'm too cheap to pay 650 to get it fixed for something i can just monitor and add oil when it needs it. may go weeks before it loses a quarter quart. i don't see a rime or reason to it's oil loss lol. seems to like to sit on the 1/4 quart low mark for a long time before it moves again.

Last edited by Joes74challenger; 01-06-2017 at 01:32 PM.
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post #12 of (permalink) Old 01-06-2017, 04:11 PM Thread Starter
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Quote:
Originally Posted by jtrosky View Post
I use 93 octane (Mostly non-TopTier now since I work from home now and there are no TopTier stations around my home) and I average about 22mpg - mostly 35-45mph country roads with very little highway driving. I have VERY little oil consumption and VERY little oil in my intake tube when I check it. I honestly think that the more "aggressive" that you drive, the more oil will end up in the intake due to increased vacuum because of heavy throttle. No evidence to support that - just makes sense to me.

50k miles on my 2012 LT - purchased with 19k miles. Engine power and gas mileage are the same as when I bought the car.

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I don't know this for sure so don't hold me to it. But I disagree on the aggressive driving and oil consumption. I say this only because according to my scan tool data the highest vacuum pressure or air pressure getting sucked through the intake are at lower RPM, using that logic it would speed the oil consumption and draw more oil into the engine. Like I said this is just a half educated guess. At idle I will show about 8psi but at 3,000 rpm it will be 1 or 2 psi.

I do agree with you in the other post that someone asked about the valve coking problem that it all depends on the specific car. I think you got lucky and aren't experiencing any of the problems others are who have excessive oil consumption. My question is what's different about each engine that makes some of them ok and others develop a serious problem? They're identical in every way. The only thing I can think of is I drilled the holes on the dirty side of the pcv barb slightly larger, another forum member posted a thread about the factory holes being too small and getting clogged. But I don't see how that could cause this kind of problem.

I did some math and a cold check of my oil to get the most accurate reading. I figured in 375 miles 3 ounces of oil just disappeared, I know it's in the pcv system and intake somewhere. I know this doesn't sound like much but figure that's 16 ounces in 2000 miles, that's 2 cups of oil dumped right into the engine. Yes a catch can is the answer but then the powertrain warranty becomes a problem. I know it's a rock and a hard place and there's not a whole lot that can be done. Even induction services aren't good because they can break carbon off and scar cylinder walls.

My next battle is to deal with Chevy, I've had good luck because I've been a GM owner my whole life and my parents business has several GM vehicles. I'm going to see if through them I can get my valves manually cleaned, or at least get the dealership to take a serious look at things. They tend to take the lazy way out, if there's no check engine light they will say they can't duplicate your issue, which is their favorite saying. I may try one more seafoam service myself now that I've got a way of getting it into the TB.
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post #13 of (permalink) Old 01-06-2017, 06:14 PM
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^ Normal vacuum gauge readings on a properly running engine are as follows: Idle-18-22. Deceleration-22-30. Economy (Cruising)-10-18. Power-0-10.

Last edited by sheila; 01-07-2017 at 08:47 AM.
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post #14 of (permalink) Old 01-06-2017, 07:14 PM Thread Starter
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^ Normal vacuum gauge readings on a properly running engine are as follows: Idle-18-22. Deceleration-22-30. Economy-10-18. Power-0-10.
I'm not sure where my scan tool is getting the information from. I think it's the intake, because it says intake air pressure. So would that be the same as vacuum? And if so what would cause it to be so low?

I have a manual vacuum gauge, where would I connect it to check vacuum? I was thinking I could use the main line right off the brake booster, but I'm not sure if that full engine vacuum or not?

Last edited by kb3gup; 01-07-2017 at 05:22 AM.
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post #15 of (permalink) Old 01-07-2017, 07:49 AM
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Any vacuum port on the intake manifold. May use a tee fitting.
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