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2008-2013 Cadillac CTS General Discussion Discussion, Horrible Gas Mileage 10 AWD 3.6 Wagon in Cadillac CTS Second Generation Forum - 2008-2013; Originally Posted by Jorf I understand it's a large engine, but man those numbers just seem low to me. The ...
  1. #46
    snofun3 is offline Cadillac Owners Fanatic
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    Re: Horrible Gas Mileage 10 AWD 3.6 Wagon

    Quote Originally Posted by Jorf View Post
    I understand it's a large engine, but man those numbers just seem low to me. The car doesn't behave how I'd think that it should. I've pulled better MPG driving a dodge viper around for a weekend, and you'd better believe I wasn't being "nice" to that car's pedal!
    It's not a large engine, it's a mid-sized engine. I have a new Nissan Pathfinder rental right now with the 3.6 engine, and not only is it's performance FAR better than the CTS (in a straight line at least), it's getting about 20-21 around town and 28 on the highway. My old Maxima that could run circles around the CTS with it's 3.5, and routinely got 22-24 around town, and up to 30 at a constant 60.
    My Jag XF with a 5.0 gets 19-20 around town and 25-26 on highway, and you'll NEVER confuse the performance of the CTS with the Jag.

    My CTS also got abysmal mileage, so much so that I couldn't even keep the mileage indication on. It would be one thing if the performance was astounding, but it's not, so you just have to get used to it.

  2. #47
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    Re: Horrible Gas Mileage 10 AWD 3.6 Wagon

    Quote Originally Posted by Jorf View Post

    I know that part of what may be affecting my mileage is that I drive in Ann Arbor, Michigan, and there's actually quite a few hilly streets here. While I acknowledge that the hills probably contribute, there's no reason for me to be achieving 10-13 mpg city.

    Looking at the insti-mpg though the vehicle just looks wrong to me... as soon as I touch the gas pedal, it'll drop to 18 mpg (this is egg-under-foot touching, just enough to make the engine do something... not really even accelerate). If I have to press hard enough to actually accelerate (slow acceleration, like 1mph/s), it'll drop to 13 mpg, and accelerating harder than that is even worse. Pedal on the floor acceleration earns me an instant rating of 2mpg.
    I don't think that's really that unusual. I would notice that in my previous CTS (2012 Premium AWD Coupe) and I had a lifetime average of 21 mpg over 21,000 miles (I'm practically your neighbor live in Northville).

    We also have an X5 (3.0T) and the same thing, just touch the pedal and it drops down into the high teens, the turbo isn't even spooling up yet. Any semblance of acceleration will go to single digits, but once you are cruising it'll swing the other way.

    I have posted before and I'll say it again, AWD in these cars is brutal if you do a lot of stop and go driving and I would imagine the hills make it worse. Prior to the CTS, I had an Acura RL with SH-AWD. If I did any sort of stop and go driving I would get mid-teen mileage, overall I would get between 21-22 mpg and once on a road trip I got as high as 27 mpg.

  3. #48
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    Re: Horrible Gas Mileage 10 AWD 3.6 Wagon

    Quote Originally Posted by Jorf View Post
    I've got a 2010 AWD 3.6 premium wagon that I just bought about two months ago. It's got just over 30,000 miles and is a CPO vehicle now that's covered under warranty until November 2015.

    Since getting the car, the city MPG has been the baying my existence. I've been seeing numbers between 10-13 mpg city. It's absolutely abysmal.
    I hate to need to bicker with the dealership again, since I just got it back from being rear-ended at a stop light a few weeks ago. But, I suppose I might ask them if there's anything they know about. I've been using 87 octane fuel, and no matter my driving style (egg under foot, hard driving, pulse and glide) the MPG is really about the same, and I've never seen anywhere near the window sticker numbers.

    I can't really comment on highway mileage because I haven't been able to take the car on a decent trip yet (It was in the shop being repaired from the accident when I had to go to my parents' place for thanksgiving, so I took the loaner).
    jorf.....just to humor all, try this. Have an upper induction cleaning performed (no additives to the fuel tank, just treatment through intake tract via vacuum). Run 87 near empty. Fill with 93. Reset all MPG log and post your results.....see what it does and share please.
    RX Performance Products/RevXtreme.com 941-721-1826

  4. #49
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    My AWD Chevy gets 11MPG, I blame my right foot. But I has 400nsum Horsepower so I don't care.

  5. #50
    Jorf is offline Cadillac Owners Member
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    Re: Horrible Gas Mileage 10 AWD 3.6 Wagon

    Quote Originally Posted by SC2150 View Post
    jorf.....just to humor all, try this. Have an upper induction cleaning performed (no additives to the fuel tank, just treatment through intake tract via vacuum). Run 87 near empty. Fill with 93. Reset all MPG log and post your results.....see what it does and share please.
    I agree that this would be interesting to see the results of, but I don't have the extra money at the moment to do something like this. (I'd love to just do it myself, but I don't have a garage to work in, I live in a condo.)

    I'll be doing a long trip this coming weekend, ~1400 miles round trip to upstate NY and back, so I'll see what kind of long distance mileage I can pull off.
    When I get back, I'll talk to the dealer and see if they can do anything for me under warranty.

  6. #51
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    Re: Horrible Gas Mileage 10 AWD 3.6 Wagon

    I don't believe having the upper induction cleaning done will pay for itself. As far as increasing the octane from regular to premium is simply a waste of money if you are simply running an unmodified engine with the factory ECM. All you are going to do is waste more money. The manual says regular so the computer is set to run on regular. The extra octane produces no more thermal output.
    Pushing the use of premium has been quite prevalent on this forum but time and again no one has produced any documented proof that an increase in octane on a factory, unmodified engine has produced any performance gains let alone any mpg gains.
    For the most part you fuel efficiency is based on you. How you drive, your area (stop and go or all highway) weather are all things that will effect your mpgs. run it , enjoy it, and don't worry about it.

  7. #52
    Cougar281 is offline Cadillac Owners Fanatic
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    Re: Horrible Gas Mileage 10 AWD 3.6 Wagon

    Quote Originally Posted by C "T" ess View Post
    I don't believe having the upper induction cleaning done will pay for itself. As far as increasing the octane from regular to premium is simply a waste of money if you are simply running an unmodified engine with the factory ECM. All you are going to do is waste more money. The manual says regular so the computer is set to run on regular. The extra octane produces no more thermal output.
    Pushing the use of premium has been quite prevalent on this forum but time and again no one has produced any documented proof that an increase in octane on a factory, unmodified engine has produced any performance gains let alone any mpg gains.
    For the most part you fuel efficiency is based on you. How you drive, your area (stop and go or all highway) weather are all things that will effect your mpgs. run it , enjoy it, and don't worry about it.
    Do you have any proof of this, or is it 'because it's in the manual it must be so'? The LLT is a very high compression motor (11.4:1). If the LLT was a SFI motor like the LY7 instead of DI, it would almost certainly require 91+ octane to live. The old Lincoln Mark VIII's with the DOHC 4.6L (9.9:1CR) required 91 octane to not detonate. Computer controls have come a long way and can help stop detonation before it causes damage, hence how the LY7 can run 87 at 10.2:1CR, but you can only go so far. I'm SURE the LY7 is pulling all kinds of timing all the time to keep from detonating.

    I haven't gotten too far into testing, but I can tell you for SURE that the LLT's are pulling timing a LOT. So far I have done some logging with 87 and have seen as much as 7* or timing being pulled due to knock. I'm currently on my second tank of 89 and haven't logged much, but initial logs show what may be a little drop in timing being pulled, but it's not gone. In a bit I'll move to 91/93 and see what I get as far as knock retard.

    If it goes away completely on 93, then despite the manual saying 87 is recommended, these engines really should be running on 93. When the computer pulls timing, that pulls power, efficiency and economy. Granted, if your foot's planted on the floor, your economy is going to suck, but if the computer is pulling timing 50%+ of the time while you're just cruising on the highway, your economy will suffer.

    I've attached a screen shot of the knock retard from a four and a half minute drive. There is quite a bit of detonation being detected, causing timing to be pulled.
    Attached Images

  8. #53
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    Re: Horrible Gas Mileage 10 AWD 3.6 Wagon

    Cougar, that screen shot, that's with 87 octane, correct? When can you get the 93 (or 91) posted, and can you do both in the same post?

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    Re: Horrible Gas Mileage 10 AWD 3.6 Wagon

    And why would GM recommend an octane rating that would actually reduce efficiency. I'm not saying you're wrong about timing but again with mpg such an issue it would would seem that the octane choice would be the fix and customers would be advised to change. Also, switching to 93 octane going be cost effective vs increase in mpg's. As far as engine life, GM is on the hook for 10 years/100,000 miles, maybe it's a crap shoot that they are willing to take as related to engine repairs.

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    Re: Horrible Gas Mileage 10 AWD 3.6 Wagon

    While some have argued, I have found that the gas mileage does improve using premium. This was multiple tanks driven over nearly identical conditions, under suburban and highway driving. I did the testing so that it would be statistically significant, with many tanks of gas. I found the improvement on my 2010 AWD wagon to be more than enough to justify the higher cost for premium.

  11. #56
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    Re: Horrible Gas Mileage 10 AWD 3.6 Wagon

    Quote Originally Posted by sliderule01 View Post
    While some have argued, I have found that the gas mileage does improve using premium. This was multiple tanks driven over nearly identical conditions, under suburban and highway driving. I did the testing so that it would be statistically significant, with many tanks of gas. I found the improvement on my 2010 AWD wagon to be more than enough to justify the higher cost for premium.
    Your experience is not consistent with the vast majority of scientific tests of premium vs. regular gasoline. Here are a couple of references:

    http://www.cartalk.com/content/premium-vs-regular-0

    http://www.csmonitor.com/Business/In...as-saving-tips

    http://www.edmunds.com/fuel-economy/...g-premium.html

    http://money.msn.com/saving-money-ti...a-b30bf27a090f

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    Re: Horrible Gas Mileage 10 AWD 3.6 Wagon

    Quote Originally Posted by Cougar281 View Post
    Do you have any proof of this, or is it 'because it's in the manual it must be so'? The LLT is a very high compression motor (11.4:1). If the LLT was a SFI motor like the LY7 instead of DI, it would almost certainly require 91+ octane to live. The old Lincoln Mark VIII's with the DOHC 4.6L (9.9:1CR) required 91 octane to not detonate. Computer controls have come a long way and can help stop detonation before it causes damage, hence how the LY7 can run 87 at 10.2:1CR, but you can only go so far. I'm SURE the LY7 is pulling all kinds of timing all the time to keep from detonating.

    I haven't gotten too far into testing, but I can tell you for SURE that the LLT's are pulling timing a LOT. So far I have done some logging with 87 and have seen as much as 7* or timing being pulled due to knock. I'm currently on my second tank of 89 and haven't logged much, but initial logs show what may be a little drop in timing being pulled, but it's not gone. In a bit I'll move to 91/93 and see what I get as far as knock retard.

    If it goes away completely on 93, then despite the manual saying 87 is recommended, these engines really should be running on 93. When the computer pulls timing, that pulls power, efficiency and economy. Granted, if your foot's planted on the floor, your economy is going to suck, but if the computer is pulling timing 50%+ of the time while you're just cruising on the highway, your economy will suffer.

    I've attached a screen shot of the knock retard from a four and a half minute drive. There is quite a bit of detonation being detected, causing timing to be pulled.
    This is what we see on ALL of these, and the intake valve coking when it reaches a certain point it will have such a negative effect that nothing can help short of a manual intake valve cleaning (see the thread with pics on this forum). On the dyno we see the detonation and timing retard as well, but on the street we really see this. Again, the ECU/PCM is set from the factory to allow optimum performance and economy with 93, but the engineers are NOT the ones that tell you to run 87, the marketing brains are. Same with the inferior dexos rated syn blend vs full syn when the blend will result in timing chain issues, etc. as the DI V6's are far more advanced in design than the V8. Thanks for the graphs, and we have seen this so many times over the years I turn blue arguing. Now, if this was a lower comp V8 or the LY7, then 87 is all you need. But at 11.3-11.5:1 there is no way to NOT get more power and MPG with a octane to match.

    Quote Originally Posted by C "T" ess View Post
    And why would GM recommend an octane rating that would actually reduce efficiency. I'm not saying you're wrong about timing but again with mpg such an issue it would would seem that the octane choice would be the fix and customers would be advised to change. Also, switching to 93 octane going be cost effective vs increase in mpg's. As far as engine life, GM is on the hook for 10 years/100,000 miles, maybe it's a crap shoot that they are willing to take as related to engine repairs.
    Again, it has nothing to do with what is best for the engines performance or economy, sales are targeted to the budget minded that could not afford a V and that goes for the cheaper fuel and oil...all marketing, not engineering. ONLY a lower compression engine like a 9-9.5:1 CR engine will running more than the proper octane not only be a waste of money (like the links below explain), but can even lower your MPG due to the slower, more controlled burn of the higher octane. We as a society sure get brainwashed so easily....is it better for us to spend $ on our credit card we dont have to just to get redeemable points for something or just spend less to begin with? If you believe what the adds tell us, spend all you can, pick up your sisters lunch tab as it is all just "using her for points" ! And Obamacare really didn't double our health ins premium and give us a greater deductible, going to $987 a month VS the $523 we were paying for a better plan w/lower deductable is all in my head...he promised it over and over in his speeches I followed over the past few years, and still claims this is not so....but I can't seem to get the ins company to listen either.
    Quote Originally Posted by The_Judge View Post
    Your experience is not consistent with the vast majority of scientific tests of premium vs. regular gasoline. Here are a couple of references:

    http://www.cartalk.com/content/premium-vs-regular-0

    http://www.csmonitor.com/Business/In...as-saving-tips

    http://www.edmunds.com/fuel-economy/...g-premium.html

    http://money.msn.com/saving-money-ti...a-b30bf27a090f
    Again, these are all referring to the lower compression ratio non-DI engines. If we see it right there on the laptop screen as we log and tune these, it sure isn't because it is some conspiracy, this is fact and anyone wanting to see it in person stop by your tuner and ask them to do a short log while driving to show you. If these were older lower CR engines, this is all absolutelu true and anything more than 87 is a pure waste....but these are 11.3-11.5:1. Why is the new 2014 LT-1 at the same CR (11.5:1) requiring 93 ONLY then? the knock sensors on any of these newer engines will detect detonation and pull ignition timing quicker than the human ear can detect so there is no physical harm or damage done, but if the engine is not running at optimum timing (look at a LS based V8 timing tables...both high and low octane tables...look how much less timing is in the low octane tables) it is impossible to get optimum power and economy. I think the biggest misunderstanding is most are confusing the older lower compression port injection engines with the new high compression DI engines.....so it is critical to differentiate just as the port injection engines can run 100-200k miles with zero deposits on the intake valves if a good top tier fuel is used where this has zero effect on the excessive coking buildup on a DI engine in as little as 10-15k miles as the fuel never touches the intake valves now, it is introduced directly into the compression chamber in the final 20-30% of the compression stroke. And at 2000-3000 PSI the injectors never get dirty and deposit clogged like they did at 45-55 PSI of old.
    RX Performance Products/RevXtreme.com 941-721-1826

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    Re: Horrible Gas Mileage 10 AWD 3.6 Wagon

    You fail to account for how the direct injection engine works. In a normally aspirated engine, fuel is injected into the compression chamber and then compressed significantly prior to ignition. The higher the octane rating of the fuel, the more it can be compressed before it spontaneously explodes; low octane gas ignites prematurely in high-compression engines, causing knock and a loss of power, whereas high octane gas can withstand the high compression of the engine without exploding before the intended point. However, in a DI engine, such as the CTS's 3.6DI, the fuel is injected directly into the compression chamber under extremely high pressure at the precise moment of ignition; there is no further compression before ignition. Consequently, a lower octane fuel can be used without pre-ignition or knocking. Using a higher octane fuel in such engines accomplishes nothing -- higher octane fuel is NOT inherently more powerful; it's simply able to withstand greater compression before explosion in a typical, non-DI engine -- it's the engine, NOT the fuel, that generates more power. Again, that's all irrelevant in a DI engine.
    tinman, C "T" ess and snofun3 like this.

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    Re: Horrible Gas Mileage 10 AWD 3.6 Wagon

    all this injector cleaning talk- my wife's cts4 coupe has been getting about 15 around town since the day it came off the lot- so no dirty injectors there. Her car has about 14k miles as of now and I did a 400 mile trip Christmas day and managed 20.4 according to the DIC.
    I cant say that was terrible considering the speeds I was driving and due to the hilly terrain and passing others was downshifting a good amount of the time but its still lousy fuel economy but by comparison her old Lexus ES ( ok its was FWD not AWD ) would get 30 cruising at 85mph

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    Re: Horrible Gas Mileage 10 AWD 3.6 Wagon

    I think by now we are seeing many different opinions on this topic. Some are vehement about stance than others. While I tend to side with the expert reports presented in this thread, that is because they support my position. We can probably continue this argument well into the future without resolving anything to everyone's satisfaction. MPG will always be a concern especially since some get better mileage than others. Is the original posters perhaps related to the fact that he is hauling around a heavy car with AWD. I don't know and apparently no one else has come up with an answer that is acceptable to most. It's probably best that each of us make our own informed decision based on what we know and just go with it.

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