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Discussion Starter · #1 ·
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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Discussion Starter · #12 ·
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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Discussion Starter · #14 · (Edited)
^ 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?
 
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