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Old 08-05-2013, 11:25 PM   #1 (permalink)
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91 Octane "recommended" for 2014 MDX

Is the engine in the 2014 MDX tuned to run OK on regular gas? The glossy MDX brochure says 91 "recommended." My old Acura RSX said "required." My understanding of the difference between these is that an engine will run fine on regular if 91 is recommended (albeit with a small loss of performance.) But regular gas in an engine that requires 91 is bad for it in the long term.

I asked at the dealer and the salesman dodged the question saying "Just use 89 and you'll be fine."

So recommended or required?

I pick up my new MDX in two days. I'll probably put 91 in it all the time anyway, but I'd like to know if I have an option.
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Old 08-06-2013, 12:23 AM   #2 (permalink)
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You've made the decision to purchase an expensive new car....even if it were okay to pump 89 octane, why skimp on the fuel choice? I'd spend the extra ~$0.10/gallon on 91 octane for best results.
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Old 08-06-2013, 12:33 AM   #3 (permalink)
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You can put whatever octane you want as the car will run on 87, but performance and gas mileage will be worse with the lower octanes.

Common thought is why buy a 40-50k car yet try to save a few bucks at the pump every week. I tend to agree with this. I've only used 93 octane (91 isn't available).
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Old 08-06-2013, 10:15 AM   #4 (permalink)
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I'd spend the extra ~$0.10/gallon on 91 octane for best results.
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Old 08-06-2013, 11:32 AM   #5 (permalink)
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You've made the decision to purchase an expensive new car....even if it were okay to pump 89 octane, why skimp on the fuel choice? I'd spend the extra ~$0.10/gallon on 91 octane for best results.
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Old 08-06-2013, 03:47 PM   #6 (permalink)
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I think it's best to do a couple of calculations here to quantify it -

I just returned from about a 1,000 mile trip in the 2014 MDX. I noticed that premium gas, although annoyingly more expensive than regular gas, was roughly about 5%-10% more expensive.

The vehicle managed just about 26 mpg on that drive according to the on-board display.

Acura states that 'use of gas with an octane lower than 91 will result in decreased engine performance' and I think this will likely translate into lower mpg (I haven't tested it - just an educated assumption on my part).

It wouldn't take much of a percentage drop in mpg (1.5 - 3 mpg) to overshadow any savings in fuel costs so going for the cheaper gas may be a wash in the end yet you'd be left without one of the attributes of buying an MDX over an econobox - performance.

The other calculation -
- Assume premium costs about $.35 more per gallon than regular
- Assume you'd drive about 15,000 miles per year
- Assume 22mpg overall
--> 15,000 miles/22mpg = 681 gallons
--> 681 gallons x $.35/g = $238
That's $238 more per year in fuel costs over regular (even assuming no mpg dip for going to regular which is unlikely).
- Assume you drive the vehicle for 7 years (I randomly picked that value to get to about 100K miles).
--> The extra fuel cost would be $238 x 7 = $1,666.
- Assume the cost of the MDX is about $44,000 (varies depending on model so I picked somewhere in the middle).
--> The extra fuel cost over the lifetime of the vehicle is roughly 3.7% of the price of the vehicle. This amount to almost a rounding error on the MDX and is within the typical negotiated cost difference range - i.e. the difference between paying MSRP versus the 'internet/fleet' price. It's also substantially less than some of the options people pay for such as normal to tech or tech to advance or fwd to awd.

It'd be interesting if someone here would do some reasonably accurate testing - do the same tests with both premium and regular (the tank would have to be nearly empty in between and filled to the same level for the tests) to see what the mpg difference is between the two and what the 'seat in the pants' performance difference is between the two. I won't do it to mine because I always want the performance and am willing to pay a bit more for it even though it's still annoying to pay the premium price.
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Old 08-10-2013, 09:18 PM   #7 (permalink)
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Over the years, I have read several detailed tests in car magazines like Road & Track regarding the performance of engines "designed for premium fuel" that tolerate regular fuel (presumably due to anti-knock sensing in their engine management systems). These tests carefully compared power and fuel economy using premium vs. regular fuel and showed actual dynanometer plots. Unfortunately, those articles do not appear to be available on the web and I discarded my car magazine collection a few years ago. For normally aspirated engines, the impact of using regular gas was small: 1-3% loss of horsepower and no detectable difference in fuel economy. Pinging with regular gas was not a problem. Note that using regular fuel does not force the anti-knock sensor to retard the timing under most circumstances. In the old days before computer-controlled engine management and precise fuel injection, engines that knocked did so under certain conditions (typically high load and low rpm).

The only legal difference between fuel sold as premium vs. fuel sold as regular is octane, which is not a measure of fuel "quality". Years ago, there was slightly more energy per unit volume in regular gas than in premium gas; the compounds that were blended to create higher octane gas had less energy than the gasoline they replaced. The simplest and cheapest way to raise the octane level of gasoline is to add more ethanol (which has a high octane rating but contains less energy per unit volume than gasoline). But government regulations now force nearly all gas (E85, which contains 85% ethanol, in not gas) to contain about 10% ethanol; more exotic compounds with energy content close to that of gasoline are used to raise the octane rating. So the energy contents of regular and premium gasoline are very close and depend on exactly what compounds are used to raise the octane level.

Major oil companies like Chevron, Shell, and Exxon advertise that they put more additives (e.g., polyetheramine [PEA] sold under various brand names including Techron) in premium fuel than in regular fuel, which is probably true. But the EPA mandates the same minimum additive levels in regular and premium fuels so it difficult to know whether an engine is really getting extra additives with premium fuel---particularly if the fuel is not "Top tier". I believe most of what the major oil companies say regarding fuel quality. "Top tier" fuels are generally better: more carefully made with superior additive packs. For this reason, I would feel much more comfortable running a car for which regular gas is acceptable using "top tier" regular gas than off-brand (e.g., Costco) premium.

The best online discussion of regular vs. premium that I have seen can be found at cartalk.com: Premium vs. Regular | Car Talk.

Let me back up my opinion with a bit of personal experience. I own a 2007 Honda Civic SI Sedan. For MDXers who never deign to enter a Honda showroom, the Civic SI is the only credible successor to the now defunct Acura Integra GS-R. My Civic SI has a power band very similar to the 1996 GS-R that it replaced, but a higher redline and a little more horsepower to go with it. I ran my Integra GS-R on regular for the last five or six years that I drove it with no detectable ill effects.

The gas cap on my SI says "Premium Fuel", but if you read the fine print in the owners manual, any fuel above 87 pump (or AKI) octane is satisfactory. I bought my car in January 2007 and I have run at most 3 or 4 tanks of premium fuel in the car since I bought it. I cannot tell any difference between regular and premium despite the fact i routinely wind the engine to over 7000RPM (the Civic SI has very little torque but it is fast if you drive like a crazed adolescent). Am I sacrificing some performance? Almost certainly. Based on the magazine tests I have read comparing engine power curves on a dyno, I am probably losing .1 to .2 seconds in a full throttle 0-60 run. But I rarely engage in full throttle runs to 60 mph; it is hard on the clutch. (The Civic SI is only available with a 6 speed manual transmission. Automatics cannot cope with an engine that is a slug at 3000 rpm and a screamer at 5000rpm.)

I do not yet own an MDX but my wife dearly wants one and the 2014 model is almost fuel efficient enough for me to justify buying a FWD model with almost no options---particularly when I take into account the value of marital peace. The most logical alternative is a Honda Odyssey EX-L, but it is far larger than what we need to accommodate a family of five not-very-big people. Moreover, my wife suffers from minivan phobia and she would much prefer to drive almost anything other than a minivan. I can empathize; she has been driving a 2003 Mazda MPV for the past decade.

My family and I are spending this calendar year living in Sweden. If we were living permanently in Europe, we would almost certainly buy a Ford S-Max Titanium. Even Jeremy Clarkson loves the S-Max. But no S-Max is available in the US, so an 2014 MDX is looking increasingly likely.

If we buy a 2014 MDX, we will almost certainly fuel it with regular gas. I was briefly back in the US (more specifically The Woodlands, TX) last week and I was shocked to see that premium gas now costs $.40 more than regular, a difference of more than 10%; regular gas costs slightly less than $3.50. I suspect that the oil companies are making a much higher profit on premium than regular because the demand for premium is not very elastic and stations typically advertise the price of regular making cost comparisons for premium more difficult. Oil companies understand consumer psychology well and exploit it when they can. Many of my friends work in the industry. (The Woodlands is a beautiful planned community built on the prosperity that flows from the oil and gas industry.) Next time that i have a chance, I will ask about the profit margin on regular vs. premium. Many, many people believe premium is much better than regular and worth the price differential, even when it is $.40 a gallon. In general, I don't. Unless I am filling up a car that absolutely needs premium (like the chipped 944 Turbo S Porsche that I owned two decades ago), I will use regular.

Here in Sweden, regular gas costs at least $8.15 a gallon. In Stockholm, $8.75 per gallon is typical. I generally don't look at the price of premium. Our 2006 Opel Zafira with a 2.2L DI engine (a GM Ecotec, ugh) runs on regular.
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Old 08-10-2013, 10:37 PM   #8 (permalink)
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My Civic SI has a power band very similar to the 1996 GS-R that it replaced, but a higher redline and a little more horsepower to go with it.
Your 2007 Civic Si has a lower redline than the 1994-2001 GS-R (8000 RPM vs 8100 RPM, respectively).
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Old 08-10-2013, 10:38 PM   #9 (permalink)
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You can put whatever octane you want as the car will run on 87, but performance and gas mileage will be worse with the lower octanes.

Common thought is why buy a 40-50k car yet try to save a few bucks at the pump every week. I tend to agree with this.
This post says it all.
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Old 08-11-2013, 12:30 PM   #10 (permalink)
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We're using regular in the 2014 MDX from the outset. Power is fine, and mileage is in the mid-20s highway, high-teens city.

We used premium in our 2011, and to those who argue that the engine requires premium fuel for maximum power and gas mileage, I disagree - we got 14.8MPG over 31,000 miles, and it was terrible in the power department - you had to jam your foot to the floor to accelerate on the highway.

Maybe we'll try out premium in the future or mix 87 and 93. But a savings of $700 (30-35 cent spread between regular and premium) is significant.
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Old 08-11-2013, 02:28 PM   #11 (permalink)
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to those who argue that the engine requires premium fuel for maximum power and gas mileage, I disagree
You can choose to believe the actual design engineers or not.

The following is from the owner's manual -
Quote:
Unleaded gasoline with a Pump Octane Number (PON) of 91 or
higher is recommended.
Use of lower octane gasoline can cause occasional metallic
knocking noise in the engine and will result in decreased engine
performance.
Use of gasoline with a pump octane less than 87 can lead to
engine damage.
What I was wondering is if anyone here quantified the effect of the lower performance on gas mileage through fairly controlled testing. Just saying you used premium on a previous vehicle and you didn't like the power doesn't mean anything in this regard. You'd need to do fixed tests both with 91 and with 87 to be able to quantify it.
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Old 08-11-2013, 03:22 PM   #12 (permalink)
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What I was wondering is if anyone here quantified the effect of the lower performance on gas mileage through fairly controlled testing. Just saying you used premium on a previous vehicle and you didn't like the power doesn't mean anything in this regard. You'd need to do fixed tests both with 91 and with 87 to be able to quantify it.
The problem is that nobody can truly control their testing. People don't spend entire tankfuls driving exactly the same roads in exactly the same traffic and weather conditions. Those other variables - the roads you drive, the traffic, the weather - introduce too many sources of differences. Those who keep track of their mileage (including me) typically find differences of 2-5 mpg from one tankful to another, sometimes with no obvious cause, just random variations.
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Old 08-11-2013, 04:00 PM   #13 (permalink)
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^^ I agree it's not easy to do fairly controlled testing which is one reason why I'd lean towards the manufacturer's recommendation (who does the engineering as well as the tightly controlled testing) over someone's 'feelings'. However, if someone actually tried to quantify it I'd be interested in the numbers even though, as you say, there are a lot of variables including traffic, driving style changes, temperature changes, etc.

Mostly I wanted to point out that there's a correlation between engine performance and efficiency and hence mileage. Whether it's significant or not is what I don't know and have never seen quantified - i.e. are people paying 10% more on premium fuel but also getting a 10% improvement on mileage and noticeable performance gains, or are they paying 10% more on fuel and getting a 1% improvement on mileage and no noticeable performance gains? It'd be nice to know the answer.
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Old 10-15-2013, 12:17 AM   #14 (permalink)
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The above extensive post by ponderosaTX agrees with my decades of experience. I drive the same route over most of the year and for years and get very consistent gas mileage. With the exception that mileage drops a bit in the winter (it maybe partly related to oxygenated fuels).

I can not measure a difference in mileage or feel a difference in how the car performs. This was/is on a 2004 TL. I normally run regular so this was my baseline. Three tank fulls of premium were run and the average mpg for the total of the 3 full tanks was the same as what I get with regular.

The on line 2014 MDX manual reads:

■ Fuel recommendation
Use of lower octane gasoline can cause occasional metallic knocking noise in the engine and will result in decreased engine performance.
Use of gasoline with a pump octane less than 87 can lead to engine damage.

Running what is recommended (premium) is a very reasonable choice! Running below 87 octane (sea level) is not smart. I keep cars 200k + miles (buy new) and have seen no issues running regular in cars that recommend premium and have heard no knocking. The cost of running 2-3 cars (family driving up to four cars) with premium versus regular over decades is significant. I choose to spend the money elsewhere.
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Old 10-15-2013, 08:53 AM   #15 (permalink)
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I use 87 octnae in my 2014 and it runs great. I had to use 91 or higher octane in my 2009 MDX because it ran like crap with anything less.

Use what ever works for you its just a car!
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