danmangto

2013 RDX using cheap regular 87 octane gas. 630 mile road trip and got 29.1 mpg, hand calculated. This is with 3 people and luggage and a speed of around 65mph on the highway portions and some traffic in areas. I'm impressed. Since the sticker rating is only 27.

Mike_TX

So this was basically two tanks of gas (?) Did you notice any pinging or reduced performance? Or do you run regular gas all the time?

danmangto

Yes, 2 tanks of gas. No pinging, engine runs fine. I've only used regular 87 since getting the RDX about 4 months ago. The performance is ok. To me the RDX is barely ok or adequate, performance wise... I'm used to much more powerful cars.

Dimcorner

Nice!

I'm thinking of going 87 as well. Figure this is the same engine in an Accord, with the same compression ratio, and the Accord still gets more power.

I too consider the RDX adequate since I'm not really flooring it anyway.

tal

I've run my RDX AWD with 87 octane since new. It now has 6k mi. Runs fine for me. No detonation and no issues.

I drive this vehicle as transportation. It rarely sees above 4k RPM and is driven like an old lady.

If you drive 'spirited' then you may benefit from the higher octane stuff.

DeMAN

TX, stick with 93 octane. I have for 9 years in my TL with a similar engine.

You never know how you have to drive. It nice to know you don't have to worry about looking at the RPM gauge in order to accelerate.

singlecoilpickup

I believe you can use 87 on the RDX and never give it a second thought regardless of driving conditions. The engine is made and tested for 87 octane. It's not going to start pinging on 87. If it weren't Premium would be required and not "recommended."

DeMAN

Wow how times have changed. Noboby would have made that statement a year ago or so on this forum. I guess it took Hyundai/Kia to give Acura owners some b***s to use 87 octane gas. I had a thread at one time about this very subject. I was told "dont buy an Acura if I can't afford premium".


I will have to agree with the manual in "recommended".
However "recommended" means to use the recommended grade of gas. This applies to oil also. Can other oil than recommended be used, sure, but 5w-20 is whats recommended.

singlecoilpickup

The service guy at the dealership, who I've been using for years and is very good, insisted that using 87 or 91 should make no difference in the RDX.

In my TL I always used Premium, but in the RDX I haven't either since both the sales guy and my service guy insisted there's no reason to use Premium. They said when corporate first delivered the car to them they had a training session on the '13s and corporate told them that using 87 should be no issue.

Modern car computers are very sophisticated and adapt to the octane that you're using. The only real exception is if you've got a turbocharger or supercharger. In the RDX case, you don't really even take a performance or MPG hit as far as I can tell.

I can certainly afford premium, especially since I don't drive often and don't have to gas up often, but I don't really see much reason to throw unnecessary money at the oil companies.

ipribadi

Reliability:
Most modern engines have knock sensors which will retard the ignition timing to avoid any long term reliability issues. So regarding reliability, I think this is a non issue for any late model Acura.

Performance:
To my understanding the use of premium gasoline is necessary for high compression engines (11.0 ratio above in gas injection engines and 12.5 ratio above in direct injection engines) as it will allow the most optimal ignition timing.

Such high compression engines can operate on lower octane but will result in pinging/knocking unless the ignition timing is retarded allowing the combustion to begin later at a point where the chamber is expanding faster. This results is a drop in performance.

In the RDX's case, the engine ratio is 10.5 which is the same as many regular gas 3.5l V6 Honda engines, thus it is believed running 87 octane in the 2G RDX does not result in such severe penalty in performance relative to other higher compression Acura engines.

Okay, so that's all the theory ...
Thanks to the OP confirming the real world condition

geocord

The new Skyactiv DI engines from Mazda have a compression ratio of 14:1 in their gas engines and use Regular gas. I know they have did a lot of engineering to accomplish that and since they are fairly new so maybe time wil tell. They have been out only about a year or so.

Dimcorner

Mazda did some black magic with their long tube headers for that. I do remember when test driving it thou that it sounded like a diesel almost.

Also as a note the US version is 13:1 compression, not 14:1. I believe it's because they wanted to use 87 in the US.

geocord

Still over 12.5:1 and still high. I forgot they reduced the compression for the US version as I had read about awhile ago. Regardless of how they did it, they did it! I drove the CX-5 before I drove the RDX and don't remember any diesel like noise at all. In fact it was very quiet as the salesman and I spent a lot of time at idle talking and I could hardly hear the engine. I liked it but it didn't have enough power. If they had had the larger 2.5L engine that they put in the 2014 CX-5 I might just have bought that.

danmangto

I believe the 2013+ RDX is only tuned for 91 octane or less. I believe 92 or 93 octane is just a waste of $$.

I had to nail the gas this hard this morning, hit nearly 6k rpm... it still performed perfectly and had decent acceleration on the 87 octane.

danmangto

LOL.. I can afford Premium gas, I chose not to If I don't have to. After driving my 2013 RDX with Premium the first month, than regular 87 the last 4 months, I see no diff in gas mileage or acceleration or drivability. It still has same decent acceleration when I need to hammer it.

fleuger99

I've used Premium for the first 6500 miles. My last three tanks have been mid grade or 89 and I've not noticed any difference in performance. Getting same average mileage, same responsive engine and no pinging.

I use about a tank a week and here I save about $12 per month or $144 per year. I totally agree its not a lot of difference but I'm leasing and don't see why I should pay more if I am seeing no negative effects.

Mike_TX

I'm slowly coming around, too. Up to now I've figured it didn't really cost that much more to use Premium, but there is some satisfaction in selecting the lower-priced gas at the pump. I filled up with mid-grade this last tank, and I'll see how it does. Next time I may go all the way and get regular.

One step at a time.

aquaholik

Got 3500 miles on mine now. At first I thought for sure I would get better mpg with premium. I alternated between premium, 89, and 87 using Shell gasoline. Doesn't seem to make a difference at all in hand calculated MPG which is typically .4 to .5 mpg different than the display. I am averaging 22.4 on the display but I think it is close to 22mpg. I do more city than highway.

The last 4 tanks have been nothing but 87 Shell even though gas priced have dropped. I have not noticed a single change in MPG or performance decrease. Most of the time I drive with an eye on the MPG average but sometime I just said the heck with it and just step on it.

Also I can confirm that 29mpg on the highway on a short 50 miles trip using regular gas.

fleuger99

Hey Aquaholik,

What speed were you averaging to get 29mpg? I commute to work 4 times a week. It is 46 miles each way and 90% interstate. I do average 75-80 Mph and the best I've seen is 25.5Mpg. Thanks.

aquaholik

About 70-75 Mph. I live in Florida. It is FLAT here. Watch your fuel economy gauge. It should occasionally hit 40-60 mpg when you are feathering the gas pedal. I am driving solo most of the time. Will have to take a road trip to Rainbow spring for a 100 miles highway trip with the wife and kid and see if additional load will matter much. They only weigh 180lbs combine so I doubt it.

Towing a small boat however kills the highway mpg. I am getting 20 mpg towing a 500 lbs trailer and 400lbs boat. I was expecting 22-24 mpg.

fleuger99

Cool, thanks for the info. Today I filled up just outside of the office and reset my odometer. When I got home I had averaged 28Mpg, my best ever. There was traffic so I only managed 70Mph average so maybe this helped.

CoachRick

If you start feeling guilty, remember our Texas 'premium' is 93(central TX anyway), so you could compromise and blend with 89 for the 'luxury' octane rating.

Closing in on 9000 miles with about 90% 'regular' petrol use...no complaints...avg is just under 22 with some 'spirited' driving.

Mike_TX

We're almost all 91 octane up here in the DFW area. It goes 87-89-91. Out in the Panhandle Premium drops to 90 and Regular to 85 at most stations!

Wonder who decides what octane rating we get?

GRDX

United States: in the US octane rating is displayed in AKI. In the Rocky Mountain (high elevation) states, 85 AKI (90 RON) is the minimum octane, and 91 AKI (95 RON) is the maximum octane available in fuel[http://en.wikipedia.org/wiki/Wikipedia:Citation_needed]. The reason for this is that in higher-elevation areas, a typical http://en.wikipedia.org/wiki/Naturally_aspirated_engine draws in less air mass per cycle because of the reduced density of the atmosphere. This directly translates to less fuel and reduced absolute compression in the cylinder, therefore deterring knock. It is safe to fill a carbureted car that normally takes 87 AKI fuel at sea level with 85 AKI fuel in the mountains, but at sea level the fuel may cause damage to the engine. A disadvantage to this strategy is that most turbocharged vehicles are unable to produce full power, even when using the "premium" 91 AKI fuel. In some east coast states, up to 94 AKI (98 RON) is available.[26] As of January, 2011, over 40 states and a total of over 2500 stations offer http://en.wikipedia.org/wiki/Ethanol-based E-85 fuel with 105 AKI.[27] Often, filling stations near US racing tracks will offer higher octane levels such as 100 AKI

Source:
http://en.wikipedia.org/wiki/Octane_rating

Mike_TX

Yeah, but we're a whopping 650 ft. above sea level and we get the same max octane as Denver? LOL

CoachRick

HEY! We've got 50 feet on you!(on average). I don't recall NOT seeing 93 at any station in Austin; but I'll admit to frequenting the same half-dozen Chevron or Shell stations when convenient.

Mike_TX

I misspoke - I was at a station today that has 93 octane. I guess we get a mix of 91 and 93 in these parts.

danmangto

My commute is only 21-22mpg, it's only 12 miles each way and it's 50%, 25mph stop and go zones and 50% highway speeds. Close to the EPA mixed 22mpg rating. It sure beats the 16 to 17mpg my old EX35 would get in the same commute.

Stump

...used 87 octane on my 2003 MDX, and also my 2007 MDX...all good. And have continued on my 2013 RDX. Have notice zero, repeat zero diff from 92 octane.

So you're going up a mountain, hauling a 1200 lbs boat, then maybe 90+ octane...otherwise, why?

Manufacturers 'recommend' much stuff...i would too in their place. But doesn't mean required...my 2 cents........

Dimcorner

I just did a trip from Columbia to Greenville and back (110) miles.

87 Octane
Going there (little bit in a hurry) got 28.4 averaging 64mph
Return trip got 31.0 with 62mph average (more city driving since it was dinner rush in downtown greenville). I felt the return trip was more down hill.

This is all from the computer reading, haven't filled up yet to see the impact.

ipribadi

Okay ... all this 87 octane talk has gotten to me too.
Filled up 87octane first time last week (always had 93 octane).
So far half tank thru and negligible impact on mpg and couldn't tell any difference in pickup.

At worst it could be half mpg lower, but then again the heat has been picking up lately so the A/C must be working harder too.

Mike_TX

I'm still feeling a difference in power. It''s small, but it's there. I had 4 adults in the RDX the other night, and doing things like accelerating onto freeways, etc. required more accelerator than with Premium. I just felt like I was having to put the whip to it more than usual, and the exhaust note seemed a little more pronounced.

I think it shows up more with a load like I had. In stop and go traffic you're not going to notice it too much, but load it up and push it and you'll appreciate the little extra grunt you get from high-octane gas.

That said, I'm going on a 1200-mile round-trip run to the coast this weekend and I'm going to run Regular gas. It's all flat land, and the 32 cents a gallon price difference will buy dinner.

ipribadi

I think this matches what I understand about high octane usage.

At low throttle angles, the combustion pressure rise is relatively low thus no pinging even at low octane.
It's only at high throttle angles where the combustion pressure rise is high that high octane is needed to resist pinging.

So perhaps the ECU ignition mapping for lower octane gas is only modified for moderate to high throttle angles thus with easy driving usage, the difference is minimal and only with strong acceleration usage is the performance difference noticable (in both power output and mpg)

BLEXV6

If you can afford to buy the RDX, why not put in the recommended fuel? Yes it costs more but who cares. I am no Engineer, but the Engine is tuned for premium. If it did not need premium I am sure Acura would say so, because gas prices are high enough and they finally went to the trouble of deactivating cylinders to save gas. If this was a major issue for me I would have bought the CRV.

AnalogDE

Agreed with BLEXV6. You just dropped 35K+ on a car, and you're worried about ~$200/yr added cost of Premium over Regular...You should've gotten the CRV if money is that tight.

Rocketsfan

Weird. I could've sworn every Exxon I usually pump at is 93 octane in the DFW area. I know when I go to the NW Arkansas area, that drops to 89 or something. I'll have to pay more attention next time I go to see what the max octane I'm pumping is if for no other reason than curiosity.

CoachRick

Here we go again. I reckon folks should spend their hard-earned money any way they see fit. However, one does not buy higher quality petrol when purchasing 91 or 93 octane; one is simply using fuel that performs differently(maybe). If there were a quality difference, I'd be all over the higher rated fuel(unless there were no downside to the use of the lower quality). For my dollar(or three or four), a top-tier fuel that performs properly in the RDX is more important than a higher octane rating, especially if that higher octane is contained in a lesser-quality fuel(no-name brands, etc).

In the broad scheme of things, my SIG 229 might be compared to the RDX in terms of positioning and quality. There is no reason in the world to shoot premium match-quality ammo through that pistol when decent quality, clean ammo is available for a much lower price. The match-grade target ammo isn't necessarily cleaner, more accurate or more powerful...the factory retail ammo performs adequately for the vast, vast majority of tasks. Now, if I'm going to haul a full load of people and cargo up a mountain, I'd likely put 93 in the RDX because of the extra stress on the engine(and we agree load is a significant factor for this discussion,I believe), much the same as I would use a 'match quality' target round in my SIG if I were pushing for maximum accuracy at a great distance. It might only add up to a few hundred dollars a year for the more expensive ammo, but I'm shooting a $900 pistol, right?

Just to run 'our' numbers again...two vehicles with similar fuel needs(Volvo 2.5l turbo and RDX V6), 35k miles per year total, 35-40 cents/gal difference in 87 vs 93 octane. ~1600 gallons of fuel X ~.38 difference =~ $600 or one month's car payment or 6 months of insurance coverage.

I don't mind saving that. Having $90K in cars is no reason to toss away money.

Dimcorner

Because it's not required, just recommended. My S4 is required because if you don't you blow the engine. The argument of affording the RDX and fuel price should also not apply. You don't HAVE to put premium and the engine is the same one from a 2012 accord (271hp/254tq v6) so I don't think the tune is all that different. I can afford to eat out during lunch at work but I choose not to.
I can afford Starbucks coffee as well but I choose not to.

$200 bucks here and there add up eventually. Most millionaires in the US are not in that category because they piss away money but because they know how to save and spend. I could have afforded a Q5 or RX, but the RDX was the best bang for the buck for me. Hell I know a doctor that makes >$300,000 per year but had to sell his M3 because he could not afford his income tax for the year.

geocord

I love my RDX but it is not a $100k plus luxury performance vehicle. It's an entry level luxury CUV. These arguments that because you spend $35k on a vehicle so you should spend as much as you can on gas are stupid. I guess if you can afford to go to a really nice restaurant you should always get an expensive appetizer and lobster bisque because you can afford it. LOL. I'm sure these same people are telling their neighbors that they should have a lawn service because, after all, they could afford the house......... Blah, blah, blah. It's just people thinking they are smarter than everybody else and wanting everyone to be the same as them. Nobody on here was telling anybody they shouldn't put premium in their vehicle. They were just reporting their results with regular. These forums are not for telling other people what to do or to insinuate someone is being stupid or cheap for wanting to save a few hundred bucks a year. If I didn't want to save a few hundred bucks I would have bought an RX or Q5. The RDX is a great value in the category, hence many people are buying it for the value AND the FACT that Acura dealers and Acura say you can use regular with no damage to your engine but maybe a little less performance under heavy load. I drive myself around with no load 99% of the time.

Having said all that, I actually use all three grades of gas kind of depending on where I get it and what the going price is at the time. I buy midgrade from a quality brand most of the time though.

ipribadi

It's more than about saving $. To me it's a philosophy that I can get something equally well for less $ spent. It just seems smarter to me.
Like the above poster said, I don't mind eating out at work, but I chose to bring my own lunch to save a bit .. not about $ but about sticking to a philosophy for chosing the better value.

This is the same philosophy that led me to choose my RDX over a used RX350 or Q5.