horseshoez

iTrader: (2)

Does the 2013 RDX engine call for Premium fuel? If not then you're simply wasting your money regardless of how you drive.

Tech

That was back in 2022. This year I got 469 miles and when I filled up, I really was running on empty as it took over 16 gallons. Next time I'll bring a 2 gallon gas can. This was all on single lane road cruising at mostly 55 - 60 mph.

And I still use regular gas.

Alex Medeiros

That's what is recommended since the car is tuned to run the best on it. Why make your car run worse and get lower MPGs to save like $2-$3 every time you fill up? That's how I look at it at least...

Tech

Running on high test does not get you more MPGs as I once thought it should after one of the vehicle engineers at work told me otherwise.

I've been running regular for a few years on my RDX driving normally and my second to last fill-up of mostly highway driving over 4 dsys got me 469 miles on 16.2 gallons.

Kelsen

Around here, premium is 50 cents a gallon more; that's 5-8 dollars a fillup, and that adds up. If there were any clear advantages, I would do it more often. But I don't see or feel them.


RFT!!!
Dave Kelsen
--
"My mom is convinced I have narcissistic personality disorder, but I'm pretty sure I'm too awesome to have that." -- Adrienne Airhart

horseshoez

iTrader: (2)

Not sure where you're getting your information, but the odds are pretty good the vehicle will get better fuel economy on regular.

emry

I've never used 87 but occasionally 89 when gas gets really expensive. Other than that has always consumed 91 and higher.
I can tell the car's performance using 89 was lower than when I use higher octanes. If performance is not an issue, then I guess using lower octane is fine since the knock sensor adjusts the timing of combustion. Overall, I think there is a reason that the manufacturer recommends using higher octane. All of these aside, I think the amount that is saved by using lower octane gas does not affect anyone's wealth or life is any noticeable manner and that's why I stopped using the lower octane and these days I go with 91 and higher only.

Tech

How did you measure that and what do you mean by "performance". I mean an RDX isn't really a performance vehicle as far as acceleration and top speed is concerned.

I keep very accurate fuel records from day-one and fill my gas tank equally each time. Looking at my fuel records for the same time of the year and on nearly empty fill-ups (more accurate that way) while on long trips, I get better gas mileage using 87 than 91, not by much but by an extra 3-4 MPG consistently and it has never been the other way around. So better mileage and I am paying less per gallon sounds like a win-win to me.

horseshoez

iTrader: (2)

One thing lots of folks don't realize is Regular actually has more energy per unit than Premium. The difference is the additive package; said additives to NOT have any power potential themselves, that and they displace fuel which contains all of the energy. When running around doing my day-to-day driving in my TL I used Premium, however, if I was doing a road trip I always used Regular; the best my car ever got on Premium for a full tank was 33 mpg (about 450 miles), however, on one long road trip I exceed 500 miles twice, the first tank yielded over 36 mpg.

emry

Wikipedia states: "Octane rating does not relate directly to the power output or the energy content of the fuel per unit mass or volume, but simply indicates gasoline's capability against compression. Whether or not a higher octane fuel improves or impairs an engine's performance depends on the design of the engine."

Acura engine design recommends higher octane for better performance. To me when I used 91 or 93 I simply felt the car runs smoother especially on highway.
Did I scientifically measure it? No but I expressed my own opinion and experience not a scientific fact.

Tech

Bingo!

Sunoco has a plaque on their pump handle "Per 4 Mance" making people believe that if you use their high octane, an engine that does not require it will produce more power. Pure BS. The only way 91 or 93 enable more power is if it is used in an engine that requires it.

Alex Medeiros

When you run lower than 91 octane, your car runs with less power and has to retard the timing to accommodate it. Ultimately any time I ran regular on my RDX when I had it, it just felt worse on the highway and my fuel mileage would take a 1-2 MPG hit since I had to give it more throttle to the pedal. With premium I was paying maybe $2-$3 more and not worrying about my car running poorer to save a few bucks. Don't forget that while Honda & Acura used the 3.5 V6 in their platforms, the RDX was tuned to perform the best with 91+ while maintaing the best gas mileage possible. The Hondas with the same engine only required regular gas, but they were tuned to be less powerful.

Kelsen

Fair enough. Here is an Exel file showing all the information I have up until my vehicle was above 150,000 miles. Note that the difference in mileage per gallon was never a discernable, deciding factor. That's why I quit buying it (although I have had one or two fillups with premium since then, but they are not yet in this chart.)


Dave Kelsen
--
"I'm Hub McCann. I've fought in two World Wars and countless smaller ones on three continents. I led thousands of men into battle with everything from horses and swords to artillery and tanks. I've seen the headwaters of the Nile, and tribes of natives no white man had ever seen before. I've won and lost a dozen fortunes, killed many men and loved only one woman with a passion a flea like you could never begin to understand. That's who I am. Now, go home, boy!" -- Second-hand Lions

emry

Second that. That's also exactly my experience with premium vs regular. My car doesn't show the same power with regular.

horseshoez

iTrader: (2)

Your information is incorrect. The thing is, unless your at or near full throttle, there is no need to pull back timing even with Regular fuel, and given Regular fuel has more power by volume than Premium, if you're on a long road trip, you will virtually always get better fuel economy with Regular.

RayNA

What is your car, a Vette?.. lol, you have an RDX and you don't race with an RDX, so called "loss of power" wouldn't mean anything even if it was true. I've been pulling my boat with my RDX for the last 10 years on regular, never felt like it needed any more power to pull my 16' fiberglass boat, but hey if you have money to throw SHELL's way, sure go ahead, I'll stick with cheap Pioneer regular.

Alex Medeiros

Exactly my point. When giving it full throttle you're losing the horsepower & torque. Gas mileage is typically reported as worse when using an octane less than 91 on the RDX throughout multiple forums and articles. A simple Google search will pull up multiple results stating "The motor has knock sensors and will retard the ignition timing to burn lower octane fuel, but you'll get less gas mileage and less power."

horseshoez

iTrader: (2)

Patently false; written by someone who doesn't have a freakin' clue what they're talking about.

Tech

You'll love this investigative report by Marketplace.

From 1:19 to 3:20 it is a hoot what people think, usually totally non-technical and non-scientific types and especially that yoga instructor's comments (she was probably on weed...lol).

Then at 3:49, you have an instructor at this institute leading the blind once you see the results between regular and premium. Of course the numbers are the same between regular and premium.

Tech

Having been in the measurement business running a lab, mind you an electrical standards lab, the methods are the same when taking measurments in order to keep errors down.

When I fill-up, I do so on a nearly empty gas tank, about 16 US gallons or 60 liters and most of the time I am at 15 US gallons or 55 liters per fill-up. Then you have different pump nozzles at different stations with different sensitivities as to when they shut off. For that reason, I fill it up till I can not longer get gas into the tank because a 4L out of 60L is already 6.67% difference in the fuel for example. Yeah yeah, I have heard all about evap issues filling it to the brim but in well over 24 years, I have never had an evap code or problem.

Then I look at my mileages under the same conditions: same highway, same speed on cruise where everybody is passing me, and temperature.

And you'll notice in the video above, the instructor states at 4:50 "and using that much fuel", except nowhere on his PC screen does it show fuel consumption. Man the poor man is what I call "the blind leading the blind". On top of it, the only way to cruise at 50 kph and lower HP is if you reduce the friction in the vehicle (drivetrain) as there is no aerodynamic drag.

Kelsen

It's worth noting that for the overall mileage figure (not the per tank number, although if you fill it up the same way each time, you'll be pretty close for comparisons), as long as you track the total miles traveled and the total amount put in, you'll have an accurate total mpg, even if you vary from filling it half way, or always $10.00 worth, or any other variation. But if you want numbers for specific conditions, you have to fill it up when those conditions change.

I have known that there isn't any 'premium' achieved by using premium gas for many decades, and the numbers in that Excel chart back that up, although that chart is only 34,000 miles worth. I have the same info on my previous car and my current motorcycle.


RFT!!!
Dave Kelsen
--
Long night, I woke up in some Japanese family's rec room... and they... would... NOT... stop... screaming.

Alex Medeiros

You can literally look it up. I'm just telling it how it is, with YOUR WORDS. I agree you don't have a clue...

horseshoez

iTrader: (2)

Look what up, words of other clueless individuals? Why don't you try using an authoritative source. While I agree engines designed for Premium fuel put out more power when at full throttle, I submit at partial throttle, say rolling down the freeway at 20% throttle, a high AKI rated fuel will provide exactly zero benefit.

emry

This is a technically incorrect statement. It entirely depends on the internal design of an engine as how to extract max power from specific gas octane. You simply can't put 87 in any engine and expect to get the most MPG and power out of it. RDX internal combustion is designed to deliver the best power/performance with 91+ octane not lower. The knock sensor will adjusts the timing so the engine will still work with 87 but not at the same performance rate. For the record, I get 30 MGP with 91 octane but only 27 MPG with 89 octane. Have tried this many times.

horseshoez

iTrader: (2)

Clearly you don't understand internal combustion engines; at partial "freeway speed" throttle there is no way for detonation to happen on one of these engines. As for your trying, my tries contradict yours; the J32A3 in my TL was not significantly different than the J35Z2 engine in the RDX, however, the J32A3 has a higher compression ration than the J35Z2 (11.0:1 vs. 10.5:1), after running 93 AKI for my first several road trips I switched to 87 AKI fuel for such trips and was stunned at how much better mileage I got. I had predicted little if any change, however, the results speak for themselves; as I posted above, the best my car ever got on 93 AKI was 32 mpg, the best my car got on 87 AKI was 36 mpg; a pretty significant difference.

Tech

Which is why I use the same conditions every year at the same time of the year when I head to the track and hotel plus 2 days heading from the hotel to the track and back to the hotel and then the drive home on the fourth day....469 miles.

I will use premium in the Porsche and the motorcycles because they are driven differently. In the Alps where I will be driving slow in the hairpin passes (hot running engine) and on steep grades with my air-oil cooled BMW and heavily loaded at 1000 pounds two up and luggage, I'll be using Super Plus 98 (about a 93/94 in our numbers) to a 102. But I am not worried about mileage, even on the Autobahn. There is no knock sensor on it.

Alex Medeiros

That's exactly the point I made. I rest my case.

horseshoez

iTrader: (2)

I have never said otherwise; if you think I have, you're welcome to search for yourself. I have always maintained for fuel economy on a long road trip, Regular will always meet or exceed the fuel economy of Premium fuel; and each time I stated that, you argued. I rest my case.

Clickit02

I tried many times alternating between 93 and 87 in my 2016 RDX, filling up from about 1/4 tank to full. Driving on freeway or mixed driving, I found ZERO MPG difference between either gas (better say no measurable difference). Remember, driving on freeway at 75mph your engine runs at about 2000rpm, and it is not at its maximum power. MPG depends how we drive. Drive aggressively, and it will go down. With “normal” driving there is no reason to waste $$ for 93.

Tech

Alex, just wondering, but how often are you on full throttle aka WOT? Yes, I know all about needing premium for an engine that does need it to arrive at its full potential, but it is useless in engines that don't and even motors where premium is recommended (RDX) when I am not loading the engine heavily as in pulling a heavy trailer up a steep road or trying to do a quarter-mile time.

In about 6.5 years of ownership, I never have been at WOT, not even close. So I don't worry about it and if needed that 0.000001% of the time, my knock sensors will take care of it for that 5 or less seconds of WOT. I know I am barely pressing my gas pedal down. And I have no problem merging into the left lane for a left lane turn.

Where I live the difference between regular and premium is about $0.66 per US gallon. Not a big deal at an extra $10.50 a fill-up, but why blow money with no needed gain. Hell, to fill my motorcycle in Europe ran me €69.05 or about $75...no choice in the matter if you want to drive the best roads.

Alex Medeiros

I utilize my engine as much as possible, mainly on the highway when merging and passing the MAssholes on the road. For me I like to get the best performance possible out of my vehicles, so I try not to cheap out on things like gas, oil, etc. Currently with my Mazda CX-5 Turbo I would be losing like 26 HP and 10 TQ going down to regular gas from 91+, but it will run fine just like the RDX. The dealer threw in regular when I bought the car after my RDX got totaled and on the highway it felt horrible until I got premium gas.

samiam_68

I run my 15 RDX primarily on premium. The few times I tried regular, I didn't notice any decrease in MPG, but I definitely noticed a decrease in power. The engine simply doesn't feel as "eager" to pull as with premium. I feel occasional hesitation (I guess due to the computer having to retard the timing) and I definitely have to lay into the gas pedal more to get the same acceleration as just lightly tapping it while on premium. On the same fairly steep highway upgrades, while maintaining the same speed, it definitely downshifts more often on regular. This is not a scientific study by any means, but I do keep track of miles/gallons/fuel grade in a spreadsheet, so I can say MPG isn't really affected by fuel grade. But the butt-dyno definitely feels power difference between different grades. To each their own, but the V6 in the RDX is an absolute gem and I don't mind spending a little extra to bring out its full capability.

emry

May be I don't but do you? From what you post I can't tell. You can express your one-sample experience as a personal opinion but it seems you tend to present it as scientific fact which no one would buy.

Obviously we are talking about RDX here not any other vehicle. That partial throttle action on highway speed engages CMS in RDX which engages only 3 cylinders to save gas and thus provide higher MPG. In any other condition that all cylinders are engaged, it means power is the main objective not MPG and that's where higher octane in RDX plays it role (based on Honda specs and recommendation).

Having said all of these, I am not interested in exchanging non-sensical posts with you or others. I am more interested in logical fact-based scientific data. If you have those or you know online references that clearly states lower octane gas generates the same power in RDX as the higher one, I like to see them.

horseshoez

iTrader: (2)

@emry, quite honestly I am not suggesting you take my word for it; I believe I posted further back in this thread you should do your own research from an authoritative source, say the SAE.org maybe. As for my credentials, I'm just some schmuck on the internet, so my credentials, or lack there of, are irrelevant (but like it or don't, believe it or not, I do have some bonafides). At this point you have my blessing to go through life ignorant.

emry

Fair enough. I think words speak for themselves. People around here judge for themselves about the ignorant one. I expressed my opinion but didn't present it as fact. That's all that matters. The rest is history. I cut this interaction here and in the future.

Tech

As the engineer who worked in the vehicle test lab where I also worked (but in a different lab) once told me, you get better mileage on regular gas at normal highway speeds.

Of course I didn't believe him when he told me that some 25 years ago. But since then I found out he is right. Under the same steady state conditions at legal highway speeds, premium does not get you better MPGs.

Clickit02

Nor does the regular. Case closed.

horseshoez

iTrader: (2)

Case reopened. The fact is Regular fuel has slightly more energy per unit of fuel than Premium.

Tech

Exactly.

Actually the engineer (and this guy was a practical engineer, not a cubicle engineer behind a desk) where I worked said all things being equal, regular gets you better gas mileage. Case closed! And sure enough, I got 469 miles on one fill-up.

Clickit02

What makes premium vs regular, 87 vs 91/93? Slightly different additive composition to clean system better and “octane booster” to increase gasoline resistance to spontaneous or premature combustion from increased pressure. Theoretically, if pure gasoline energy/unit higher vs additive energy/unit, the regular gasoline will offer better MPG. But, since additives cannot exceed 1% of total gasoline volume, it is not possible for regular driver to detect the difference.

https://www.law.cornell.edu/cfr/text...lume%20percent.

Now, do you care to explain how gasoline with octane booster can have less energy vs. gasoline that does not have this additive?

Unless you can provide simple and compelling explanation, case closed.