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Acura RDX Real World MPG



  • autoboy16autoboy16 Posts: 992
    I love my accord but cruising on the highway with the revs at 3.2k is unnerving but the engine sounds sooo sweet (until my squeal kicks in)... But i have a 4speed auto.

    I would love to get a TSX as my next car as it is a revver but I think honda/acura should be working day&Night on a 6-7speed automatic that cruises in 6th gear at around 2k-2.6k RPM. It saves gas and let others "Play" in the 4-5 gears. Watching the tac go from 6 o'clock to 3 o'clock seems cool occasionally but not always.

  • woodywwwoodyww Posts: 1,810
    I don't own an RDX, but I've been interested in them. And I read the R&T article where they got around 13 mpg, & some of the posts here about lousy mileage.

    Just an amateur guess: Putting too small of an engine in a vehicle can be almost as bad for mileage as a giant V8, or even worse. I don't understand putting a 4cyl. in a vehicle of that size & weight, with AWD yet--it doesn't make sense to me.

    FWIW, I have a bmw 5-series (6 y.o. e39) RWD wagon, 6 cyl, auto, & I average around 18.5 mpg around town, & 23 HWY. Obviously, it will get better mileage than a comparable vehicle with AWD. But since the cargo capacity is a bit more than the RDX, frankly, I'd rather get the better mileage & put on snow tires in winter.

    I'd love to know why Honda felt compelled to put a 4 cyl. in a vehicle of that size.....??
  • c_hunterc_hunter Posts: 4,487
    I have never gotten less than 21mpg and as high as 25mpg with my RDX. The engine is totally adequate and well matched to the vehicle in my opinion. I would not have minded a V6 and may have preferred it, but have no major complaints about the turbo-4. It is quite good.
  • stathisstathis Posts: 32
    I think the main reason for the low MPG is the weight of the RDX. At 3,950 lbs that's a lot of weight to move. The RDX is made mainly of steel; as soon as you lift the small hood you realize how heavy it is!
    In comparison, my BMW 540 (V8) had a lot of aluminum parts, which made it 1,000 lbs lighter.
    I don't think the AWD is a major factor. Think of the Murano analogy: the AWD is only 1 MPG lower than the FWD. They weigh 3,950 and 3,800 lbs respectively. Hence, 18 MPG and 19 MPG.

    I was getting 17.5 MPG with my BMW; the RDX gives me around the same.

    The V-6 sounds good, but all the V6 SUVs in this range have poor acceleration: Lexus RX, Murano, Highlander, are much slower.
    Hence, I am happy with the current RDX engine performance and handling.
  • 1bythesea1bythesea Posts: 52
    I've had my RDX for one month with 900 miles of mixed driving. The daily commute consists of 70% hwy/30% city, 17 miles one way with an average of 22.5 mpg. So far I'm very happy.

    I do think those of you who are getting the 13 mpg average do have something going on causing it. Perhaps the reason Acura is not doing anything is because the engine may still be within normal operating specs to them. However, if I were getting that low of mileage I would be highly upset also. Hopefully, Acura/Honda will be able to come out with a fix.
  • stathisstathis Posts: 32
    Keep in mind that the mpg given by the on-board computer might not be accurate. Mine overstates mpg by around 1 mpg. So always do the math yourselves, by zeroing out every time you fill up.
  • 1bythesea1bythesea Posts: 52
    You may be correct as other RDX owners on other sites have stated as either the on-board computer was dead-on or 1 mpg lower than actual. Manully checking is good advice.
  • blufz1blufz1 Posts: 2,045
    The basic problem is that you have a 2.4 engine trying to lug around 4,000 lbs. There's no replacement for displacement! Would be more economical w/a larger engine. It's a loser at the box office,too.
  • c_hunterc_hunter Posts: 4,487
    You're forgetting that a turbo increases the effective displacement of the engine though. It may have the bores of a 2.4L but it's got the mass flow rate of a much larger displacement (and the torque/HP numbers to back it up).
  • blufz1blufz1 Posts: 2,045
    Didn't forget. I just don't think the engineering paper design transfers to the road well in this application.
  • johnny98johnny98 Posts: 88
    There is a huge difference in 0-60mph times between the turbo RDX and 4-cylinder CRV.
  • blufz1blufz1 Posts: 2,045
    Neither car is fast to me,so that's a non issue for me and most people. They sold 17,379 CRVs last month and 2151 RDXs. I rest my case. :)
  • c_hunterc_hunter Posts: 4,487
    It's no secret that RDX sales are not great, we have hashed that out since last fall, but even if they hit their target it would still only be 3300 units a month. This segment (sport-lux) is a lot smaller that the segment the CR-V is in, thus comparing the two is not real useful. It's like saying 3" is shorter than 17" and trying to make a point out of it.

    I don't know what lofty engine specs are normal for you, but most shoppers see a big difference between the RDX and CR-V in terms of power and general sport feel. I know I did. The RDX is certainly not super fast and it's not a sports car despite what some people may think, but it's no slouch either. It's one of the best handling SUVs I have driven, and the powertrain is decent. 0-60 times in the 6 second range are still pretty good for a realistic SUV nowadays.
  • blufz1blufz1 Posts: 2,045
    I know it's a nice car,it's a Honda! I just think Honda made a mistake w/ the powerplant. I prefer not to own anything that spins at 30,000 to 50,000 rpms.
  • oncrankoncrank Posts: 8
    This may have been covered already, I just didn't feel like reading the next 100+ posts.

    People on here keep saying "well my other car didn't do this bad and I drive them both the same". Is your other car TURBO'D? If you have a firm foot off the line, doesn't have to be heavy, just firm til you hit second or third. On a turbo'd vehicle, you are engaging the turbo that much more which uses more gas. The whole idea for the reduced lag is to get the turbo goin sooner so you dont have to dip into the throttle that much. If you don't change your style of driving, you will get crappy mileage if you drive the way I explained.

    One more thing on the turbo. It is ALWAYS spinning which means you will use a bit more gas, even at low throttle or cruise.

    If Acura was REEEEALLY serious about addressing this problem they would do well to do one of a few things. One, put a better variable geometry turbo in. They make models that vary intake across all driving conditions and dont open and close one valve when a certain parameter is reached. This one has vanes that turn to allow the ideal flow for just about any driving condition. Another idea, one mentioned, is to adjust the tuning or have a knob that adjusts it for you, maybe even allow a lower octane or just tune for 89 instead of 91. The reason 86 or 87 doesn't work is because the ECU can't accomodate that degree of a difference and running for extended periods on this will hurt the engine. 89 on and off from 93 won't hurt anything. All the time, maybe it'll do some damage. One last thought that might help not with mpg, but range, is a bigger tank. Just a few more gallons as weight will become eventually become a concern.

    I don't own one but am seriously looking. What is the break-in instructions for the car? I see people who have to drive other cars a set amount of miles UNDER a certain speed in order to properly break the engine in. I'm curious if this has any bearing on what some people are doing. People are saying they do several hundred mile trips on a BRAND NEW car. That doesn't sound like a great idea to me. Any thoughts?
  • c_hunterc_hunter Posts: 4,487
    The turbo may always be spinning, but it doesn't boost all the time. When wind-milling, it has little to no effect on the engine other than a causing a slight amount of backpressure. But it's small compared to the overall back pressure of the exhaust system. The turbo will raise fuel consumption only when it is boosting in a significant way.

    There have been numerous variable nozzle / variable vane turbo designs over the years, but none have proven reliability or longevity -- they have too many delicate moving parts in a hot exhaust gas stream. One of Honda's stated goals was to make the RDX turbo simple and reliable, something that should last a long time. They just would not be able to achieve that goal with the more exotic variable geometry turbo designs. I believe that's why you never see those in production automobiles nowadays. In fact the last application I remember was one of Shelby's turbo Dodges back in the late 80s or early 90s.

    I actually appreciate that the RDX has a couple more gallons in the tank than my last similarly sized vehicle. It means I can realistically go past 400 miles on a highway trip, something I could not do before.

    The RDX has a 600 mile break-in period. They give the usual guidelines: no hard stops, moderate acceleration, no constant speeds for long periods of time, etc. There would be nothing wrong with short highway trips as long as you make an effort to vary speed once and a while.
  • blufz1blufz1 Posts: 2,045
    Check the private party sales on these cars. Maybe you can find someone who doesn't like their RDX and you can get a relative deal.
  • oncrankoncrank Posts: 8
    1989 Shelby CSX-VNT
    BorgWarner makes one built for the 2006 Porsche 911 Turbo.(last paragraph)

    About the only time the turbo would be "free-wheeling" would be at idle. With any throttle input the turbo provides some form of boost as the exhaust side impeller would be spun. From what I understand the blow-off valve on a turbo doesn't work like the by-pass valve on a blower allowing a no boost condition under cruise. It just protects from an over-boost condition. I might be wrong, my knowledge of turbo's isn't as good as on blowers. I didn't mean to say that it is ALWAYS under boost, I meant under lighter throttle conditions, it is still providing some form of boost which uses more fuel. Even only a few pounds of boost still uses a noticeable bit.
  • c_hunterc_hunter Posts: 4,487
    Well, let's put it this way -- under light throttle, the RDX turbo gauge is pegged all the way on the vacuum side. I can drive on the highway all day long in 5th gear at 70-75mph and that gauge doesn't move off the bottom unless I give it more gas to pass or something. I have had similar experiences on past turbo vehicles with a real gauge (as opposed to the RDX's -/+ cartoon gauge). When the engine is under light load at low to moderate RPM, manifold pressure is still 10-15psi or more below max boost.

    There's no way I would be getting 25mpg in this vehicle on the highway if it was boosting significantly all the time.
  • samiam_68samiam_68 Posts: 775
    You get boost under heavy throttle, under light throttle there is no boost. However, with high RPM conditions, such as driving on the highway, the turbo spins at a pretty good clip, without providing additional boost.

    Amount of boost requested is directly controlled by the amount of throttle opening. Ability of the turbo to generate the desired boost is directly related to engine RPM - higher RPM = better ability to generate high boost.

    This is why many turbo engines have lag at low RPM - high boost is requested, but the turbo can't spool up enough to provide it until the engine revs up. Newer engines usually have very good low-RPM torque characteristics to offset the initial turbo lag.
  • oncrankoncrank Posts: 8
    Ok, good info guys. So direct experience with this car states that at cruise, the turbo is providing absolutely ZERO boost. From the way I've heard other forums speak of turbos, it seemed like there was always a small residual amount of boost at cruise, maybe a couple psi which would be enough pressure to alter fuel and timing which would use more gas.

    I guess what I'm driving at is if this is a large four cylinder, shouldn't this thing be getting a little more than 21-23mpg(as opposed to your 25 which apparently is NOT the norm, I think you're experience with previous turbod vehicles gives you an advantage on how to drive for mpg(note: this is just an opinion))? I'm just trying to see where this drain on mpg is on the highway. If you're getting 25 fairly consistently I'm assuming, what are other people doing that they aren't? Not feathering the throttle enough during cruise?

    After a little more thought, the biggest thing might just be weight. Compare it to the RAV4 which is aerodynamically similar, 4 cylinder engine, the most glaring difference appears to be weight. The Rav is 400lbs LIGHTER and it's rated at 27mpg highway. Seems to me that may be the biggest reason.

    All said and done, the biggest culprits in my opinion, are a heavier suv and less skilled drivers or less mpg road conditions(ie alot of hills). As I said, if someone here can consistently get 25, where's the problem? Doesn't seem to be completely the cars problem if the turbo isn't as involved as we've discussed. Just seems to be a HEAVY turbod car with people that aren't as consistent on the throttle as they think or live in slightly hillier areas.
  • samiam_68samiam_68 Posts: 775
    Besides being much heavier than Rav4 (300+ lb), the RDX is also wider (73.6" vs 71.5") and has wider tires, resulting in more aerodynamic drag. In addition, RDX has higher performance tires than the Rav, resulting in more rolling resistance.

    Also, the RDX 4-cyl spins a lot faster on the highway than the Rav4 V6. A slower spinning engine results in more complete combustion of the air-fuel mix, in turn resulting in better fuel efficiency.

    Plus, the Toyota/Lexus 3.5L V6 is an absolute gem when it comes to power and efficiency, whereas the RDX 2.3L Turbo is a new and unproven engine. I'm sure Honda will make it more efficient over time.

    Add all of this up, and there's the MPG gap.
  • c_hunterc_hunter Posts: 4,487
    Just to throw out some mixed info -- my last car was a turbo-4, 250HP, AWD, and weighed 350-400 lbs less than the RDX. It did a little worse than the RDX on highway MPG, and a little worse yet on average/mixed MPG. But it appeared less draggy to the eye. I don't think it's easy to figure out what/why goes into overall MPG, there are just too many factors. I think the largest one is the fuel/rpm consumption and the rpm at cruise. The RDX does cruise at a rather low RPM in 5th gear on the highway, perhaps 600-700 rpm lower than my last car.
  • oncrankoncrank Posts: 8
    I wasn't comparing the V6 Rav4. If the turbo isn't providing much of anything at cruise, the engine should be comparable to another 4 cylinder like the Rav 4's 4-banger version. That's where I got the mpg from.

    "the RDX is also wider (73.6" vs 71.5") and has wider tires, resulting in more aerodynamic drag." Umm, no. Drag is figured by surface AREA, but it is also figured by drag coefficient. For arguments sake I took the two as boxes and just figured out their general area based on specs given on this site, the Rav is 32.92 sq ft, the RDX is 33.32. Only .4 sq ft of difference. The Acura is also shorter and sits lower to the ground which also has an effect on drag. Now you can argue the tires are wider as well, but with these numbers, can you really tell me there is that much of a difference? The drag coefficient of the Rav 4 is .33, I doubt the RDX's is worse than that which should makeup for the slightly larger area(it's not listed anywhere I can find). These two vehicles are as close as you can get in terms of overall dimensions. The only glaring difference is that the RDX weighs 456 lbs more(#'s from this site). You may have a point on the tire tread, but I don't know nearly enough to comment on that.

    Yea, I know it's a crapshoot trying to find the losses. The more you dig the better you make the car though, right? It still just seems that the RDX is a bit heavier and just needs a finer touch if driving for mpg. If they can lighten it, I'm sure that will make up the difference in MPG.
  • wkrd09wkrd09 Posts: 2
    My wife and I have a RDX w/TECH Package that is currently getting 20.5mpg in city driving. The RDX currently has 13,xxx miles since we got it in Sept. 2006 (We made a few trips from South Florida to Georgia). Highway mpg at the time we took the last trip was 22 @ 75mph not using the cruise control. That's 12mpg less than the 2004 TSX w/NAV we traded. The primary reason for trading the TSX was lack of power. It was a fun car to drive but it just didn't have enough power. We enjoy driving the RDX :)
  • wkrd09wkrd09 Posts: 2
    Here are my thoughts on the RDX's less than ideal fuel consumption: 1.Weight (it weights close to 4,000lbs) :cry:
    2.AWD (all wheels driving the vehicle) :surprise: 3.Tires (18" High Performance All Season) and 4.Gear Ratio (4.533-Great for acceleration not for crusin') :mad:
  • oncrankoncrank Posts: 8
    Forgot about drive ratio. Yea, it is kinda bad. The X3 gets a rated 26mpg highway with a 3.73/4.44 Manual/Auto. That could probably help with mileage as well if that was tweeked a hair. BMW lists it's Cd(drag coefficient) .35 but I didn't figure surface area. I'm sticking with all of these tend to be a similar shape so just the hard facts like weight, gearing, and the like are the real deciders here.
  • british_roverbritish_rover Posts: 8,458
    Remember the RDX only has a 5 speed aut. A 6 speed would help increase highway mileage by a few percent.
  • c_hunterc_hunter Posts: 4,487
    You guys need to go drive an RDX on the highway. In 5th gear on the highway, it's turning lower RPMs than any recent 4-cyl vehicle I have owned, in fact it's pretty much loping along. At 70mph it's turning 1900rpm. That's lower than many 4-cyl vehicles turn at 60mph! 5th gear has a tall 0.612 ratio, which combines with the 4.533 final drive ratio to net a 2.77 gear ratio. It's not enough to look at the final drive ratio, as the overall gearing also depends on tire/wheel size and the transmission gearing. For the RDX, the overall result is 27rpm per mph in 5th gear.

    As for the number of gears, 6-spd transmissions don't always use the 6th gear as a high speed cruising gear -- in fact they normally increase the number of gears to result in tighter gear spacings, not a taller cruise gear. Whether it's a 4,5,6,7 speed is not directly relevant to the rpm/mph at highway cruise -- the overall ratio in top gear is what matters. I have a 6-speed sports car and it actually turns around 4000rpm at 75mph.
  • british_roverbritish_rover Posts: 8,458
    I had a 6 speed MINI Cooper S and it was the same way. In 6th gear at 75 mph I turned around 3,500 rpms. I meant using a 6 speed set up for improving gas mileage would help the RDX a little bit.

    The reason the RDX can pull 1,900 rpms at 70 mph is because of all the low end torque it has. It has a flatter torque curve then just about any production honda engine. I think it is the first time honda has had an engine make more torque then horsepower. A little bit of tweaking might even allow a slightly lower, numericaly speaking, 6th gear as well.

    By using a 6 speed tranny though could tighten the gear ratios up some giving a slightly lower rpm in each gear and smoother shifting.
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