Midi Man

I agree they fudged the numbers. I told them on time they must had done the MPG with the car rolling down the hills in San Francisco.

ESHBG

MPG is one of the main reasons why I did not get an RDX even though the size is perfect for what I am looking for. But I am now at 95% Philly stop and go every few inches traffic so decent city MPG is one of the top items for me.

Baldeagle

Short Answer: A V6 is more efficient in city driving.

Long Answer: Internal combustion engines are about heat expansion. To produce a certain amount of power, the engine must produce a certain amount of heat, (of which only 35-38% gets converted into work.) To produce a certain amount of heat, the engine must burn a certain amount of fuel. To properly burn that fuel, the engine needs certain amount of air (stoichiometric ratio of about 14:1).

To create a given amount of heat, each cylinder in a 4-cylinder engine must produce 50% MORE heat than each cylinder in a 6-cylinder engine. Under boost, that creates an immediate problem. Each cylinder can get too hot, which at a minimum contributes to knock, and if it progresses, can lead to Low Speed Pre-Ignition and damage internal parts.

To help reduce this very rapid spike in cylinder temps under boost, the ECU is programmed to over inject fuel. That fuel, being the same temperature as the gas tank, rapidly cools the intake charge. The ECU might lower the stoichiometric ratio to 12:1 or less under heavy boost. That means the engine burns MORE fuel than required during periods of moderate to heavy boost and decreases the engine’s efficiency. The more boost a turbo uses, the less efficient it becomes, due to the need to over inject fuel to cool the cylinders.

Naturally aspirated engines don’t have to worry about the same excess heat problems and can maintain a proper stoichiometric ratio under heavy throttle. Under moderate to heavy load, like in city driving, NA engines get comparatively better fuel economy than a turbo-4 of equal power. Turbos only shine under lighter loads, like highway travel. Overall, the V6 is a better engine. Your Lexus RX 350 has an excellent V6 engine. When mated to a non-constant AWD system, it easily explains your observed 33 mpg highway fuel economy.

Changing subjects slightly, Acura’s constant AWD system seems to constantly add a little resistance to the entire drivetrain, even with highway driving. It seems to be enough added resistance that it requires just enough extra boost in "normal driving" to cross over into the “over inject” mode and eat into fuel economy. The FWD only model seems to remain below that threshold in normal driving. The FWD RDX and the older Accord Touring use the same 2.0T engine and 10A transmission. That Accord weighs about 3,450 pounds versus 3,750 pounds for the FWD RDX and has a drag coefficient of about .29 versus .32 for the RDX. The 2.0T Accord is rated at 35 mpg at 75 mph verses my observed 32 mpg at 75 mph for the FWD RDX. If you remove the SH-AWD system from the equation, the mileage numbers makes sense.

Perhaps another question to ask is why didn’t Acura’s EPA rating show better fuel economy for the FWD model. That question aside, even if drivers hypermiled in the AWD RDX, they might reach the EPA numbers. That is not right.

horseshoez

iTrader: (2)

While stoichiometric may well be 14.7:1, engines have virtually never run at exactly stoichiometric; under full power the ratio can be as low as about 12:1 (some engines run even richer), while operating at very low MAP and/or MAF (above idle) many modern engines can run up into the high teens (some even leaner).

Lots of, "well, kinda-sorta" here; I'll address the final statement; "knock", aka. detonation, is what can get generated, a heavily boosted engine will not develop pre-ignition (at any speed) unless there is damage to the engine, and once that happens, the engine typically self-destructs within a few revolutions.

This is basically a false series of statements; there is virtually no difference in air to fuel ratios under full power regardless of whether the engine is boosted or not. The way manufacturers avoid detonation (which is the real issue we're talking about) in boosted engines are as follows:

• Intercooling: a boosted intake charge at a given temperature will rise no higher than an unboosted intake charge at that same temperature, assuming of course the compression rations are the same.
• Compression Ratio: In cases where a manufacturer sells the same basic engine in both naturally aspirated and boosted, the boosted engine typically has a slightly lower compression ratio.
• AKI fuel ratings: When comparing two engines of similar output as outlined above, the V6 may well be able to run on Regular 87 AKI fuel and still yield full power, the boosted I4 engine will virtually always need 91-93 AKI fuel to yield full power.

Completely untrue.

HotRodW

It's not just the AWD, which is mostly inactive when not needed. When highway cruising, for example, 90% of the power is sent to front wheels. And it's also not just the turbocharger. Acura simply isn't very competitive where fuel efficiency is concerned. They need hybrids.

There are two premium automakers who committed to skipping hybrids during the transition to all-electric power ... Genesis and Acura. Genesis has now admitted they were wrong and are working on launching a series of hybrids as I write this. Acura remains hushed on the topic. But I have to think they're working on something other than EV's. The ZDX just isn't the draw they were hoping for, and making it a lame duck model hasn't helped. I just hope the hybrids, if they come, aren't simply carried over from Honda unchanged in any way.

anoop

I think it's a combination of engine and transmission, probably more the transmission. But that said, if you look on fuelly.com there isn't that drastic of a difference between AWD and FWD observed mpg.

I agree and was a big fan of hybrids until I started to seriously consider the NX 350h as a replacement for my 2019 RDX. At current gas prices and for normal usage, the math just doesn't add up. Hybrid is more of a feel good rather than a real money saver. At 12000 miles a year/20 mpg you need 600 gallons a year. At $6 gas (I'm in CA and price is closer to $5 right now), it's $3600 a year. If I get to 40 mpg, I save $1800 a year. If I can get the hybrid at no additional cost, I'll take it. Otherwise, I see it mostly as a "feel good" technology rather than a money saver. If they can improve the mpg of the gas engine a little, they'll be fine.

HotRodW

For some of us, burning less fuel isn't just about saving money. The best hybrids also perform better. Having better performance while simultaneously reducing my carbon footprint has real value to me, and I'll gladly pay a premium to get it. Conversely, a vehicle as thirsty as something like the MDX Type S has little chance of earning a spot in my garage unless performance is next level because it is so thirsty. It's just who I am.

anoop

Fair enough if it does something for you.

The ones that perform better are the plug ins and then you have the inconvenience of plugging in and the inconvenience of gassing up. They also are typically the worst when it comes to reliability.

For me, mpg is one consideration along with styling, how it drives, overall value, etc. I place a high enough value on it that I strongly considered the NX, but when looking at value, styling, handling, space, I just couldn't justify it over the RDX. Plus the local Lexus dealer is lousy and wanted over MSRP.

I am not at all motivated by performance and the Type S has never looked like a good value to me. The only thing I would care about in the MDX Type S is the air suspension, but I wouldn't want to pay for all the other stuff just to get that.

HotRodW

Toyota's Hybrid Max and i-Force Max powertrains do return solid performance and fuel economy. Well, they do on paper. The Land Cruiser's i-Force Max can't seem to overcome the car's brick-like aerodynamics. I canceled my reservation as soon as I saw what people were seeing in the real world. The Grand Highlander and TX seem to do pretty well though. And Acura was really onto something with the last generation MDX Sport Hybrid. Mild hybrids have their place, too. It's a small thing, but they really help drivability. Our GLE's "sail" function noticeably improves highway mpg's. Seeing 26 or 27 mpg while cruising at 80mph in a big, heavy crossover able to get to 60 in the low 5's is pretty impressive.

Texasrdx21

In Cali with the weather and charging infrastructure - I'd go Tesla Model Y Performance or 2024 Highland Model 3 Performance. Less expensive than a RDX with subsidies and unmatched performance (makes the RDX feel super slow - including the MDX Type S). But thats just me - I like performance with any energy type. However - I'd skip plus in Hybrid - what a pain in the @ss to not only fuel up - but also have to plug in to charge the battery separately. A pure Hybrid makes more sense.

anoop

I don't qualify for subsidies, although not sure if Tesla passes it on if you lease. Model Y AWD is plenty for me, don't need Performance. Love the seats. The things that kept me from buying it compared to RDX were cost of insurance, cost of tires (supposedly wear faster than normal and cost more), and the rumor that updates were just around the corner. The rumors have turned out to be false. There were some other minor things like the glass roof with no shade and the funky door handles (I've pinched myself bad on one of those one time) that also bothered me.

Midi Man

You bring up some interesting points. I know MPG is an estimate and I would expert it to be off maybe one or two MPG but not as far as it was. It's a shame that the RDX is hyped so much and really doesn't live up to the hype at least for me. What kills me is everytime you see a Acura commercial with the RDX they are driving it like a NSX and really we all know that the car is to top heavy to do that safely.
MPG alone was not the only reason I dumped the car. I had a lot of issues with the display and cracking in the sunroof.

Yes the RX 350 is rock solid. the engine is fantastic. What I really love is just that everything works and city MPG is good enough. Maybe Acura should have done there AWD system with a switch to make it front wheel drive only in the city. But I don't think that would have helped the MPG>

mantan

A FWD driving mode would make a lot of sense. When you're sitting in stop in go traffic or driving doing heavy city driving, SH-AWD is pretty useless.

I'm very close to pulling the trigger on a 24 RDX to replace my 21 TLX, my one concern is having regrets about the mileage.

anoop

it’s your call but there are enough people reporting bad mpg on fwd on fuelly so just going fwd is unlikely to be dramatically better.

mantan

Fuelly is all over the board. 2020-2022 is under 20..which isn't tenable. But most of 2023 is a combined 23...which is what I was hoping for.

May be wishcasting though....

anoop

There's going to be variations hence the YMMV caveat. But if you're buying the car hoping to be at the high end there's a good chance you'll be disappointed. Go in assuming mpg is going to be bad and buy only if you're OK with that.

Midi Man

The TLX is way better than the RDX in many ways. Take it from me and my experience with the RDX. The RDX is hyped to much for the price. Seriously Lexus are better. .
The fact alone that the RDX only has GDI and not Port and GDI is a real downer. I don't know where you live but the City MPG in real City driving is really poor. I can expect it to be off by 1 or 2 MPG but not like I was getting driving very conservatively. Very light on the throttle. Even snow mode didn't help.I think it has to do with that stupid turbo always spinning.

mantan

Thank you! This is outstanding advice. I'm probably going to pass on the RDX because I'm already concerned about the mileage. I love my 21 TLX. The residual on it in only 23k. I can keep my powder dry for something that I love rather than getting into something I'm a little lukewarm about.

And keep hoping that a hybrid RDX makes an appearance down the road.

Texasrdx21

Smart move IMO. No one buys a mid-size SUV with some performance to be super efficient. Other options out there right now, Honda CRV Sport Touring Hybrid, Hyundai Tucson Hybrid Limited to name two. Both I drove, friend have and were super nice. Plus they both average 36 mpg - which is a far cry from my 20 mpg over 25k miles.

Plus, with all the recalls and inferior reliability these days - if you have a good vehicle that runs well - keep it till you find what you want (and is not the 1st year of a new model - not refresh - been there, done that nightmare - never again).

russianDude

The SHAWD is very useful. The MPG is not great, but at the same time it matches the sticker numbers, so no surprise here

Midi Man

The sticker numbers for MPG are way better than what the car gets.

russianDude

Not for me, I get 26-27 MPG on highway with aspec shawd.

Texasrdx21

I would agree on the city and combined number, but you can squeak out 25-26 MPG on the highway with flat terrain, no wind and speeds below 71mph. Otherwise, this number are way to aggressive in regular norm daily driving conditions. Heaven forbid you are in traffic, hilly terrain or a head wind. The SHAWD is great - but it's the combo of a thirsty 4 turbo and not very efficient.

None of this would be a big issue of petrol was below $2 gal. Even electric rates are climbing for EV at home and supercharging stations - as it all comes from coal or gas to produce that energy too.

russianDude

My combined is 22-23 with a mix of city and highway. Its whats in the sticker. Did you hope car will beat the sticker before buying it? Or are you suggesting Acura cheated on MPG numbers? That is not likely, this is a strict test and penalties for cheating are substantial

Midi Man

From my experience they defiantly cheated on the Real MPG. It's just to far off. One or 2 mpg is acceptable. not 8 to 10 like the car gets.

HotRodW

Not really that strict. Manufacturers provide the MPG estimates, not the EPA. The EPA typically approves the estimates if the numbers are reasonable. Only 15 to 20% of new models are actually verified by the EPA's testing procedure.

Almatti

Texasrdx21, Around my neck of the woods, a 22 MDX Advance with low Mileage < 25K or so,there are a few at $45 to 48K + . True a few months ago , I saw circa $50K for comparable cars In Exellent condition like mine. I haven't considered a 22 or later RDX to replace my MDX (I just executed the lease extension for 6 months). I will look at the new 25 RDX when it comes out for consideration. But if there is not a real boost in MPGs over the MDX, or they dumb down the HP or engine, I would pass for the time being. There are rumblings of a 25 RDX Gas/Electric Hybrid.

Texasrdx21

With repo's at an all time high (15k-20k a day), new car lots filling up fast - all those "over priced" used vehicles have tons of room for negotiation. Quite a bit of driving difference between a big MDX and a smaller more nimble RDX. I just had a 2024 Base MDX as a loaner for a few days - felt slow and like a mid size bus compare to my RDX.

russianDude

sources for your information that penalties not strict?, also I dont see any evidence that Acura lied.

Texasrdx21

EPA MPG is not conducted in the real world, however in a controlled environment going though a stage of tests. Real world add some many different factors in that are not replicated in the EPA MPG estimates on the MFG window sticker. https://www.fueleconomy.gov/feg/how_tested.shtml

HotRodW

The test isn't that strict. I'm not one who accused Acura of lying. Just pointing out that the EPA are not the MPG/Emissions Police they're made out to be.

anoop

I get a reasonable 21-22 mpg in mostly suburban driving without really trying to optimize (i.e. I leave the engine running the heat to keep the AC going if I'm just sitting in the car in a lot checking messages). I'm not thrilled but I know I can do better if I cared enough to optimize.

This is not the car to buy for the mpg. It's among the worst right from the sticker. German cars tend to underrate a lot of things include HP and mpg so I think that makes a lot of people disappointed when they go from German to Acura/Infiniti which don't pay much attention to mpg.

anoop

IMO the only hybrids worth buying are the Toyota/Lexus pure hybrids, but you will give up on handling when compared to Acura and you will pay a premium for the hybrid.

Texasrdx21

I surely don’t think the RDX handles well. Just ok. Drive a BMW X3 M40i, Porsche Macan or Audi QS5 - now those have exceptional handling.

anoop

Rdx steering feel is definitely better than bmw and Audi. I don’t have experience with Porsche. I think it would be better but requires $$. In terms of weight balance and taking curves I think the rdx is good enough but definitely bmw and Audi are better there. But it will out do Toyota/lexus for sure.