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2008 GX gas mileage

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  • 2008 GX gas mileage

    CNG Civic (A-5) 24/36
    Gas Civic (M-5) 26/34
    Gas Civic (A-5) 25/36
    Gas Civic (2L M-6) 21/29
    Gas Civic Hybrid 40/45
    Last edited by John Mitton; 12-01-2007, 04:12 PM. Reason: Fixed formatting

  • #2
    Re: 2008 GX gas mileage

    Has anyone tried to increase gas mileage via aerodynamic tweaking? I am wondering because the Civic Hybrid supposedly has a Cd of 0.27 while the GX has a Cd of 0.31. Why the big difference? The only thing I have noticed is a small lip-type spoiler on the hybrid... and the wheel covers are different.

    I'm currently getting average MPG of ~34MPG (ODO ~ 2400 miles). I'd like to increase that if possible. It's not so much the cost as it is reducing the frequency of refueling. The kinds of aerodynamic tweaks I'm thinking of exploring are:

    1) Front spoiler / air dam / underpan mod.
    2) Lip-type spoiler on trunk edge
    3) Smoother wheel covers
    4) LRR tires
    5) Vortex generators like seen on the WRX?

    #1, #2, and #5 I was thinking of doing some experiments with aluminum or plastic angle bars, thick plastic sheet, and tape. If it shows promise, I would rig up something a little more permanent and pleasing to the eye. If anyone has tried this already, please post your results! I will post the results of my tests when I get around to it. I am thinking of trying a front underpan mod this weekend. From some articles I've read, it is not unusual to see 10% gains in MPG.



    • #3
      Aerodynamic tweaks (was Re: 2008 GX gas mileage)

      I hope I'm not off-topic. I was just thinking increased aerodynamic performance translates into better gas mileage.

      I just looked under the front bumper and the aerodynamics look pretty clean. There is a rubber lip-type spoiler extending the entire width of the bumper, wider in front of the tires. In front of each tire (front and rear), there is a small rectangular vortex generator. The underbody surface is relatively flat, i.e. nothing sticks down. It seems pretty well designed.

      The sides between the wheels is also pretty flat. The front and rear windshields have gradual angles, so flow separation probably doesn't occur until the back edge of the trunk (need to confirm this), so a spoiler there might make a difference on Cd.

      Overall, based on what I've read (admittedly limited), the aerodynamic design looks very good! I guess a Cd of 0.31 is actually not bad. It just bugs me that the hybrid is 0.27 (for your reference, a Prius is 0.26). What's left to tweak? Rear spoiler, LRR tires, slick wheel covers. Anything else? I will try the spoiler first and leave the tires/wheels for later.

      BTW, I have a 2007 GX.

      Talk to you guys later,


      • #4
        Re: Aerodynamic tweaks (was Re: 2008 GX gas mileage)

        The best thing to do is find a wrecked Hybrid and scavage the items that are unique to it. The wheels are both ultra light wieght and more aerodynamic, as well as the LRR tires. The rear lip spoiler (as you noted), and the underbody panels. There are panels under the car to smooth out the air flow. They create that "flat" look that you noted. The "strakes" (under the car and in front of the tires) are present on the '07 & '08 Civics, I can't remember if they were there on the '06. They first appeared on the S-2000 back in 2000. There are also other light weight materials and components used in the Hybrid. The name of the game with gas mileage is weight and aerodynamics. You're definitely on the right track.

        I suspect that something as simple as the LRR tires may yield around a 5% improvement, but no one has ever posted the results of that experiment.
        Once you get it all done, let us know how the wind tunnel tests come out, ok?


        • #5
          Re: 2008 GX gas mileage

          If you put a full "undertray" on the car it will overheat your interior. You need airflow over the exhaust for cooling. I've used a full undertray on my race cars before and it turned the interior into an oven. Although a full undertray is very good for aerodynamics you will have to split it or louver it near the exhaust. But I think you are on the right path.


          • #6
            Re: 2008 GX gas mileage

            I put a K&N air filter on my '99 GX, and am getting 37-38mpg (85% highway @ 75+mph) and notice beter performance.
            Before that I was getting 35-36 mpg.
            You can pick one up at just about any auto parts store, they may have to order it, and will cost around 40$.
            For a few weeks I drove 70mph or less on my commute, and gained about 2 mpg.
            BLUE 09 GX


            • #7
              Re: 2008 GX gas mileage

              That's cool! I will definitely try the K&N filter when the time comes to replace the OEM one.

              I have also heard that the mileage increases after the engine breaks in. How many miles approximately is that? I have about 2700 miles on my car presently. Can I expect to see continued improvement, or am I pretty much "stable"?


              • #8
                Re: 2008 GX gas mileage

                In my 07 I am getting 32mpg 90% freeway at 70+ for the most part. I have 13000 miles on it and its been pretty consistent on the MPG since we brought it home.

                I think its hard for the numbers to be accurate all of the time for this reason. Fill ups are inconsistent.


                • #9
                  Re: 2008 GX gas mileage

                  I guess I am lucky I can get fairly accurate numbers on my mileage, I get a consistent fill from the same pump, always 3,600-3,800 psi.
                  The one day a week I hit the Diamond Bar facility it throws the numbers off, but I can average it out for the week. Today I got 3,700 psi, instead of the usual 4,000+.
                  BLUE 09 GX


                  • #10
                    Re: 2008 GX gas mileage

                    Johnny what are you getting for MPG and how are you driving it. I am trying to decide on which year to do the Bull Run race in. Curious if the 06 and newer are getting just as good MPG as the old CVT's did?

                    2003 Hummer H2 bi-fuel
                    2000 GMC Yukon XL bi-fuel
                    1999 International 4700 dual-fuel
                    2007 Chevy Avalanche bi-fuel

                    FMQ2-36 Fuelmaker w/ 24 GGE cascade


                    • #11
                      Re: 2008 GX gas mileage

                      I read that the GX was introduced with a 1.6L engine, in 2002 it went to 1.7L and in 2006 it went to 1.8L. This might explain some of the MPG differences.

                      In my 2007 GX (1.8L), I drive pretty economically, I start and stop gently... I try not to floor the accelerator ever. I use cruise control on the highway. I do follow traffic speed, though, so the highway speeds vary from ~45MPH to ~77MPH. Based on this, and 50/50 CTY/HWY, I am getting an average MPG of 33.93 over the 3000 miles I've driven.

                      Supposedly, the 5-speed automatic improved fuel economy over the CVT... so I would guess the worst years for GX mileage are from 2002-2005 (1.7L with CVT) and the best mileage is from a 2001 (1.6L engine with CVT). Or maybe the pre-2001's are better? Ideally, someone who has driven all three kinds of GX's can chime in.

                      If you're doing a long race, you'll probably be in top gear for most of the time. In that case, maybe the 5-speed would give you the best fuel economy (biggest 5th gear ratio for the different model years)? You might consider fitting your car with LRR tires and aerodynamic tweaks to reduce Cd... but I'm sure you're considering all that. Just my 2cents.


                      • #12
                        Re: 2008 GX gas mileage

                        I actually drive with a heavy foot.
                        It is about 5 miles city driving when I leave for work, 30-40mph zones which I go at least 5 over the limit, then about 10 miles 55mph zone which I drive 65. The next stretch is all freeway, about 55 miles, and most the time I can go 75+ the whole way, about half has carpool, I use the cruise whenever I can. I exit on to a 55mph road for about 3 miles, then 2 more city.
                        Lately driving home the construction in Riverside slows to a crawl for a few miles, which doesn't help my mpg. When I fill every night it takes 3.8-4.0 gge for 142-150 miles.
                        BLUE 09 GX


                        • #13
                          Re: 2008 GX gas mileage


                          I am trying to find a real world tank range for the 07 GX. Johnny, your driving habits mimic mine. It appears you get near 37mpg in your combined mileage. IF you could get a full 8gge's from your tank that would take you 296 miles. I ask the question because I have a home/wife/kids in Grand Junction, Colorado but my office is in Norco, Ca. So I live a few weeks at a time in So Cal and travel home to Colorado. The BIG issue is that there are no refueling stations on I-70 from Richfield, Ut to Grand Junction. A full 230 miles. Plus, currently, there are no refueling facilities in GJ. IF I could make the distance to GJ I could put a PHill in my home and I'd be golden. Therein lies the issue. I can't get a real read on just how far a "real" tank load will take the GX. The legal speed on I-70 is 75mph. And there are lots of hills between Richfield and GJ. BTW, it is a beautiful drive for anyone wanting to take a scenic drive one day drive across our western US. Anyway, I've read where people only get 220 miles from a tank. That would require installing an additional tank for safety. But if a consistent 240+ miles is possible from the 07 my job is made much easier.

                          I'd like to hear your thoughts

                          OJ Sr.


                          • #14
                            Re: 2008 GX gas mileage

                            Sorry Guys/Gals,

                            I meant to say I'm interested in the mileage of the 08 not the 07! duh.

                            OJ Sr.


                            • #15
                              Re: 2008 GX gas mileage

                              Did you find an '07 somewhere?