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Pontiac Grand Prix: Real World MPG



  • chats1chats1 Posts: 158
    I have 11,500 on my 2006. I have gotten as high as 26.5. When I first got the car, I was getting 13-14. I was really surprised at that. But, I think, as you put more mileage on your car, you'll get better mileage. I did. I'm satisfied. I knew that when I bought the car the mileage probably wouldn't be as good as my 3 GTP's but I didn't care; I wanted this 8 cylinder and I also knew the gas prices would be high, but I didn't care about that either. Except for my hissing/humming I love the car. I can't help it if I'm a fanatic about my car. I said to the dealer I think I'm paranoid. They said, "you think?" They also told me to stay off of the Edmunds website. You can't believe everything you read!! Oh, well. Good luck with your car. What color is it? I like the fact that you don't see yourself coming and going. I've only seen one in a grocery store lot so far. When I first got the car and drove it down to South Jersey, my brother surprisingly said he liked it. That was quite a compliment coming from him. He used to race hsi 65 GTO. He had to check under the hood to see how they set everything up in this 8 cylinder. He was making me nervous and then all of a sudden he pulled a rag out. When preping it, the mechanic at the dealership left a red rag on the bar in front of the fan. My brother said it's a good thing it wasn't in the fan! It was red so he could see it easily. He was disgusted with that, though. Chats1
  • rayainswrayainsw Posts: 2,978
    Repost from last fall:

    GXP gas mileage November Thanksgiving 2005 trip

    The good news is that I (finally) exceeded 20 MPG for a full tank.

    The bad news is that I am afraid it is pretty clear that I will never achieve the highway EPA rating. (Unless the gas mileage improves as I add more miles – though at 7,000+ now, I doubt that.)

    I drove from Atlanta to Carrabelle, FL and back. I filled the tank once I cleared the metro area. I filled the tank again at 232 miles (last gas in Georgia) and filled again in Tifton, before re-joining I75 North for the slog home on Sunday PM. (I did not want to count that mileage, as the traffic became bad & worse – as feared \ expected.)

    I averaged these 2 fills, since they were not the pumps I typically use – and there are variances. The 2 fills = 470 miles. Total fuel used = 19.35 gal. Average MPG = 24.3. (Excel, not DIC.)

    I did not exceed 80 MPH on the Interstate section southbound. Once off the Interstate, the speed limits and (um) aggressive enforcement mean that I find 65 the highest ‘reasonable & prudent’ speed.

    A little experimenting with various steady speeds on relatively level roads strongly suggests that DoD is much more likely to engage at 60 – 70 than at any higher speeds. With resulting steep downslope to MPG as speeds rise above 70.

    = = =

    I have seen no significant difference in my MPG since then, and I am now nearly at 14,000 miles.

    I’d like better fuel mileage – but my ( um ) un-disciplined right foot and over 300 HP \ TQ suggests that I am not willing to sacrifice an occasional acceleration “burst” for another 1 or 2 overall MPG.

    Given how much fun I have when I can use my GXP’s performance, I am pretty happy with the fuel mileage.

    I will be taking exactly the same trip described above this weekend, leaving Saturday AM (early) and returning Tuesday. I will post an update.

    - Ray
    Looking forward to 6+ hours of “Quality Time” with my XM each way . .
    2016 BMW 340i
  • blckthreeblckthree Posts: 153
    My GXP has 11,000 miles, I just took a 1500 mile trip with it. Speed was average of 80mph, mpg varied from 20.5 - 23, depending on when I had a head wind. If you can keep it below 70mph, you might do better, but I can't do that!

  • gxpjoeypgxpjoeyp Posts: 38
    Hey chats mine is black on black leather all the toys except the nav...Ive only seen 2 gxp's and they were both red i really like the dark cherry color too but that only came with the tan seats ugggghhh....
  • bubbaman999bubbaman999 Posts: 54
    Lets see, 2200 miles, so far. Mostly drive to work about 15 miles each way. About 10 freeway, 5 city and I have gotten from 20.5 to 23.7 for a high. The more I drive highway the better. Usually do cruise or I speed way too much. About 65 or so and the cruise does a better job of getting MPG and DoD shut off then my foot. Any significant increase in city driving side trips reduces the mileage to the low side 19-20. Running mid-grade gas, don't know if that makes a difference on mileage. AC always on, it is already 90-100 everyday. Plan a long trip later in the summer and will let you know. But for the simple fact I have a car with so much fun to drive the fact that I get 20s MPG is GREAT. I mean fullsize, comfortable, great handling, acceleration, all for something that gets in the 20s consistently. It is only costing me 3-4 gallons more a week (about $12) over my 03 Civic SI with significantly greater comfort, less road noise, better sounds, more power....Not too shabby.

    PS Sorry to offend the younger drivers, this old man (39), still would like to see the total buyer age stats.

  • chats1chats1 Posts: 158
    My Dark Cherry has the graphite leather interior. I wouldn't like the tan either. About the ac, I use mine all the time -- it works great, nice and cold -- no problems with it at all. That would have been my first complaint, before the hissing!!! Oh, I have everything too except for the nav. system. Chats1
  • rayainswrayainsw Posts: 2,978
    Left the Atlanta area at 6 AM Saturday. Stopped to fill the tank just South of the City.

    Kept the speed to 70 – 80 to my exit in Tifton, GA.

    My speeds off the Interstate were 45 – 65. Through a number of small towns, (and later) through the outskirts of Tallahassee, south to 98, then west.

    Filled at the (next to) last gas in Georgia. A/C was on about half the time:

    225 miles 24.5 MPG (DIC – Excel: 26.5).

    Destination was Carrabelle, FL – and my hosts used their (4 wheeled & water) vehicles, while mine sat idle . .

    On the return trip, I filled the tank again in Tifton.

    23.8 MPG – A/C on this whole leg. 248 miles. (Excel: 24.5)

    Traveling North on I75 on Tuesday AM, was able to maintain a steady 78 – 80 with cruise control on for just over 100 miles – to the rest area on the Macon Bypass. Settled in at 23.5 MPG for that segment, with the A/C on.

    I was alone in the car & only had weekend luggage.

    Just a few mileage data points . .

    Over 14,000 miles on the car & just over 400 hours on the motor.
    A relatively painless journey!
    - Ray
    Happy GXP driver . .
    2016 BMW 340i
  • eagle75eagle75 Posts: 16
    My wife and I took a 700 mile trip from Wichita, KS to St. Paul, NE and back over the holiday weekend. Averaged 65-75 both ways with A/C on all the time. 27.1 mpg up, 25.5 back (DIC). Very happy with that. Best I ever got with the Bonneville GXP on same route was 23.5. 2,300 total miles on the car so far.
  • Bill,
    Did you use cruise? Mostly level terrain, I assume. Also what fuel type did you use? I think I may see a difference with premium versus mid-grade, but don't have enough samples to prove it.

  • eagle75eagle75 Posts: 16

    On cruise most of the way--pretty flat country around these parts--some rolling hills--this was an ocean bottom a bazillion years ago. I've been using regular unleaded from day one.

  • All, came up with a spreadsheet doing a little figuring on whether it is worth additional money for better gas, from strictly a MPG cost perspective. Not from a feel/power/engine health perspective. Don't have enough mileage data on my own 06 GXP, but will monitor. Thoughts? Here is the data, assuming $2.75/gallon regular unleaded. Here is the data you can plot for yourself.

    First Column is MPG with regular Gas
    2nd Column is MPG Need if upgraded gas is 10 cents more a gallon to break even
    3rd Column is MPG Needed if gas is 20 cents more break even
    4th Column is 30 cents break even

    MPG $0.10 $0.20 $0.30
    19 19.69090909 20.38181818 21.07272727
    19.2 19.89818182 20.59636364 21.29454545
    19.4 20.10545455 20.81090909 21.51636364
    19.6 20.31272727 21.02545455 21.73818182
    19.8 20.52 21.24 21.96
    20 20.72727273 21.45454545 22.18181818
    20.2 20.93454545 21.66909091 22.40363636
    20.4 21.14181818 21.88363636 22.62545455
    20.6 21.34909091 22.09818182 22.84727273
    20.8 21.55636364 22.31272727 23.06909091
    21 21.76363636 22.52727273 23.29090909
    21.2 21.97090909 22.74181818 23.51272727
    21.4 22.17818182 22.95636364 23.73454545
    21.6 22.38545455 23.17090909 23.95636364
    21.8 22.59272727 23.38545455 24.17818182
    22 22.8 23.6 24.4
    22.2 23.00727273 23.81454545 24.62181818
    22.4 23.21454545 24.02909091 24.84363636
    22.6 23.42181818 24.24363636 25.06545455
    22.8 23.62909091 24.45818182 25.28727273
    23 23.83636364 24.67272727 25.50909091
    23.2 24.04363636 24.88727273 25.73090909
    23.4 24.25090909 25.10181818 25.95272727
    23.6 24.45818182 25.31636364 26.17454545
    23.8 24.66545455 25.53090909 26.39636364
    24 24.87272727 25.74545455 26.61818182
    24.2 25.08 25.96 26.84
    24.4 25.28727273 26.17454545 27.06181818
    24.6 25.49454545 26.38909091 27.28363636
    24.8 25.70181818 26.60363636 27.50545455
    25 25.90909091 26.81818182 27.72727273
    25.2 26.11636364 27.03272727 27.94909091
    25.4 26.32363636 27.24727273 28.17090909
    25.6 26.53090909 27.46181818 28.39272727
    25.8 26.73818182 27.67636364 28.61454545
    26 26.94545455 27.89090909 28.83636364
    26.2 27.15272727 28.10545455 29.05818182
    26.4 27.36 28.32 29.28
    26.6 27.56727273 28.53454545 29.50181818
    26.8 27.77454545 28.74909091 29.72363636
    27 27.98181818 28.96363636 29.94545455

  • All,
    Just finished the first segment of a road trip. Here are the MPG results. Some city/highway, slight upgrade, Computer 24.6 Calculated 25.

    Second day: Computer: 26.9 Calculated 27.4
    Another Tank, lot of down grade: Computer 28 Calculated 29

    Don't know if I believe the calculated, tried to fully fill the tank, but wow.

    Full highway driving really helps the MPG on the 28MPG case used cruise 74mph but some segments of highway at 68 due to 65 speed limit.

    All on mid-grade gas. More later. Very happy with these numbers, plus great ride, comfy seats.

  • I hope someone might be able to help me out. I've got a 2000 Grand Prix GT, and I can't get anything higher than 20 MPG (combined) on regular gas. The car cruises (75-85 mph) between 2500 and 3000 RPM. Any ideas?
  • gxpjoeypgxpjoeyp Posts: 38

  • tlaurotlauro Posts: 504
    I only have 5k miles on mine but can say in the suburbs/city the mpg reality is horrible. There I average 13-16mpg depending on how I driver her. On the highway, much better.

    I've taken a few 2-3 hour trips to see family. My overall average then has been 24-26mpg. Mostly highway of course, but sitting at even a few lights and going around town once I get to my destination really hurts.

    Honestly, I budget my gas money on 15mpg, perhaps you can use 18 or 19 and be safe.
  • Joeyp,
    Sorry to hear about your mileage. My recent long trip got anywhere from 25-27.8 MPG depending on hills/flat terrain on mid-grade gas. Mostly doing cruise 73-75 with ac. Also think I got 28.5, but not sure on an all hwy down hill segment. Am seeing 21-22 hwy/city mix to work. But if I play with the throttle then it is easy to get 17-18. I find that cruise works much better than my best at having a light foot. Have seen an improvement sometime between 2500-5000 miles, currently have 5500.

  • gxpjoeypgxpjoeyp Posts: 38
    Thanks Bubbaman,now is the mpg your reporting according to the numbers on the dash computer or are they according to you figuring out the mpg with a calculator after your trip and you have refilled your tank? I guess what i will do is filler up and jump on I-43,I live in milwaukee, AND TAKE A DRIVE TO GREEN BAY(NOT TO SEE THE PACKERS THATS FOR SURE)I should be able to put 150 or so miles on that trip and that highway is nice and flat all the way,so i should hopefully see what you go up to 27 mpg if i got that at 70-75 i would be really satisfied....O YEA GO STEELERS!!!!

  • It is really both. I reset the computer each time and compare actual (calculated) to the computer, most of the time they are close (within .5 mpg) usually a little low, sometimes higher. I calculated a 28.5 MPG and computer said 27.1, so I don't believe I fully got the gas in on the calculated. My latest computer week of work 15miles each way, 10 miles hwy, 5 city is 21.9. I mostly use cruise on the freeway since I am not really awake at times or just dont' want to get a ticket, something easy in the GXP. Let me know if your mileage improves.

    Shamefully a Cowboys fan,
  • gxpjoeypgxpjoeyp Posts: 38

  • I thought that EPA estimates were going to get tougher this next year for all cars, expect them to go down for all. Is it 07 or 08 they were going to change.

    Question, I got 26/27 on my all highway trips using mid-grade. What I have seen in the city/hwy mix is that different grades of gas matters. I have averaged 19-20.5 for regular. 20.9-21.5 for mid-grade and 21.9-23 for premium mix city/hwy. I use cruise on the freeway since the cutoff to 4 cyl is done much better buy the computer over my foot.

    Hope this helps,
  • gxpjoeypgxpjoeyp Posts: 38
    Maybe the gas in wisconsin is lousy I dont know but I do know that I have always used premium/93 octane since the car was new,do the cruise thing on the xpway,dont hammer the hell out of it, who knows,but here in milwaukee we use that re formulated gas more expensive cause it burns cleaner so they say 75 miles north of me they use the "old" gas....GO STEELERS!!!!!

  • Interesting, noticed when the summer formulation, aka, more ethanol came out mileage dropped a little. But this weeks tank is 22.0 on premium. What is your total miles, mine is at 5600.

    Deep in the heart of Texas,

    Go Cowboys,

  • gxpjoeypgxpjoeyp Posts: 38
  • ocmike3ocmike3 Posts: 232
    I've only got about 4400 miles on my 2005 GXP. My last road trip was cruising 65mph +/- a couple mph and the 5.3L DOD returned 27.6mpg (232 miles @ 8.4 gallons premium) running the A/C for a good portion of the trip.
    I know during the winter months we have to run 10% ethanol and my mileage drops by 10 -15%.
    I do know if I let my foot control the throttle the mileage isn't nearly as good. ;)
  • rmozolrmozol Posts: 124
    I finally got an out of town trip, to check mileage. I filled in the city and headed out. For a 123 mile trip one-way, I got a measured 26.1, with 27.0 DIC. This included a couple of traffic jams, with stop and go. I used the cruise between 70 - 72. I was in a wedding procession with some 69 - 70 GTO Judges, so hit it a few times and did some burners! It dropped to 20 something (DIC) after this city driving and gas useage. Others heard this thing coming down the street too. I thought it was just loud from behind, but I guess not! On the way home, I got a measured 26.5, with 27.8 DIC. I used premium, and a light throttle to get up to speed. I only have 2436 miles on it too. I'm content with this mileage.
  • blckthreeblckthree Posts: 153
    I sure don't know how you got 26/27 on the highway, wish I could. Only time I came close to that was one day on some flat highway with a tail wind, got 25, never seen it since.

    My average highway speed is about 80mph, give or take a bit. Average mpg is about 21-22. Not bad for 80mph, but not what I had hoped for. I won't complain, it is still a nice ride and cheaper to feed than the old Yukon was.

    Just over 13000 miles now, no troubles except for an OnStar module going out. Didn't bother me, except that it had some message every time you started the car. Got tired of the car talking to me.

  • rayainswrayainsw Posts: 2,978
    "THE 07 IS 17/25 3 MPG LESS THAN THE 06"

    I have not been to my dealer since 2007s started arriving.
    Was this the sticker on a car - or "Click Here For Window Sticker" on GMBuypower or Pontiac's web site?
    ( These are often wrong. )

    The EPA website shows the 2007 as 18 \ 27 ( 21 combined )

    And on the Pontiac web site, at the beginning step of "Build Your " - it shows 17 \ 28 for the GXP.

    - Ray
    With much experience & many thoughts on MPG . . .
    2016 BMW 340i
  • rayainswrayainsw Posts: 2,978
    My gas mileage is “fine”.


    First – highway MPG: I have achieved over 22 MPG for a full tank only a few times in over 19,000 miles. They were close to ‘ideal’ “real-world” conditions.

    ‘Ideal’ “real-world” conditions - probably sounds like an oxymoron, but what I mean is: In the “real-world”, I am NOT constrained by the EPA test limits on rate of acceleration when I merge or pass or leave a traffic light. In the real world, roads have at least some traffic and I am constrained largely [ on Interstates ] by local speed enforcement rather than EPA test max speed (still 60 MPH!!) and I am free to drive with my A/C on. ‘Ideal’ conditions mean relatively light traffic, cool enough ambient temps to be comfortable without the A/C compressor running, cool enough that the air entering the motor is relatively dense, and mostly running on roads with little significant elevation change. And only me in the car, and no more than a weekend case.

    My overall fuel mileage likely now stands at close to 19.0. But if I remove a few of the ‘best’ tanks ( not typical ) from the equation, the average probably drops closer to 18.5.

    Second, I am satisfied with the overall fuel mileage, given the available performance & how often I utilize it. (Many smiles per gallon, thank you.)

    My “around town” MPG reflects the fact that I really enjoy the V8’s acceleration – feel & sound. And I use it whenever I (safely) can. And I use all of it. WOT. Often. Thus I do not achieve the EPA estimate there. No big surprise.

    [ The GXP’s acceleration is really the one dynamic performance aspect where I feel like I can legally and safely utilize 100% of the available performance = HP & TQ on public roads. Perhaps not for long at any given time, as more than 10 or 15 seconds of WOT, in second gear, will have this car moving faster than any open road speed limit in the US. But compared to lateral acceleration & braking, it is a thrill that I can regularly enjoy, asking it to deliver absolutely all the power that it has to give. In cornering, for example, I always try to leave significant margin for the unexpected & unpredictable – sand or oil or water across an apex, or another driver doing something ill advised. Acceleration is something that I can enjoy - every time I drive my GXP! ]

    Although I have seen (and quoted here) that GM states DoD can function at up to 80 MPH under absolutely ideal conditions, my feeling is that in the real world, the slightest headwind, acceleration to pass, or uphill incline, etc. will result in DoD = off.

    And the point in the fuel mileage vs MPH curve where above a certain MPH, under certain specific conditions, DoD will not engage - likely results in a sharp drop in MPG. In fact, I’d predict that it will result in a discontinuity (??) in the curve. Meaning a straight drop, where DoD disengages, then a continuation of the downward sloping curve – at a substantially lower MPG level as speed continues to rise.

    For example. One might expect a somewhat linear drop in MPG as speed rises across the range of typical US highway travel. (Yes, I know, not really linear and not over all speed ranges, etc)

    But for purposes of illustration here - If I assume that at an absolutely steady speed of 60 MPH, my GXP can achieve 30 MPG, then at 65 it might be capable of 28 and at 70 it might be 26 and at 75 it might be 24 and at 80 it might be 22 and at 85 MPH, 20 MPG.

    If DoD is operable up to 70, but will not engage starting at say 73.14159 MPH for instance, the numbers might then look like this:


    60 – 30 (DoD on)
    65 – 28 (DoD on)
    70 – 26 (DoD on)
    75 – 20 (No DoD - instead of 24)
    80 – 18 (No DoD - instead of 22)

    I am making these numbers up, but I believe they are in the range of possibility \ reality for my GXP.

    This would mean that exceeding the DoD engagement threshold would cost something like an additional 20 or more percent (24 with DoD vs. 20 at 75 MPH without DoD and 22 vs. 18 at 80, etc.) beyond the expected decrease as speed rises beyond whatever that critical speed actually is. My driving suggests that the threshold speed ( above this, DoD does not engage in ** my ** typical driving ) is between 70 and 75.

    But that’s just me speculating.


    - Ray
    Still enjoying the drive – and not obsessing about MPG . . (?)
    2016 BMW 340i
  • ocmike3ocmike3 Posts: 232
    I think the key is being able to set the cruise and let it go... I do know when I run 75-85mph I notice that the DOD doesn't kick in nearly as often as 65-75mph. I know on a couple of tanks where it was mixed city with on-off freeway romps, my GXP was lucky to get 18mpg.
  • chats1chats1 Posts: 158
    Hi! I have 15,500 miles on my 2006 GXP which I purchased last August. Car has run great and I have gotten up to 28.7 on it. Mostly highway driving. Used it alot in August going down to the Jersey Shore and the mileage was great. Can't complain at all. Chats1
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