mav238

Well, it has been 4 years with the RDX, and it's gas diet has been mainly Shell and Chevron, sometimes Sunoco, PetroCanada. But the soaring gas price has me now trying Costco gas which offers premium grade for the same price as regular at the name brand pumps.

Honestly, I have not really noticed a real difference in power, guess it is really 91 octane and not what some folks might presume "watered" down gas due to it's lower price. Seems to run as smooth as the gas from the name brands.

f1nzup

I've been using Costco for years and have never had any problems. My only complaint is that lately the spread hasn't been what I have been used to in the past.

Carbon2008RDX

I use Mobil because it's located just around the corner from where I live. Drove by it tonight and their premium 93-octane is now $4.179!!! Yikes. Its jumped like 25 cents in one week! Disgusting. We might be looking at $5.00+ gas this summer if things keep going the way they are now.

RIPHRaPH

Mobile has the right mix of detergents for me. Mobile1 for synthetic oil and Mobile for gas. Even a 5 cent spread on a fill is a whopping .75 cents.

After I went to synthetic oil my mpg went up over 2 full miles to a shade over 26mpg.

Quick math.
An extra $30 in oil yields 2 more mpg. That translates into a little over 30 extra miles per tank.

That's 52 fills a year for me vs 60. 8 less fills x now $55.00 fills = $440.00 per year savings.

Can I squeeze more savings into filling at Costco? Maybe. Maybe not.

RIPHRaPH

But .75 cents a fill x 60 fills = $45 per year for not getting Mobile.

mav238

I save $4-5 a week pumping costco gas here in Canada. Assuming I pump 52 times a year, that's $200-250! Way more than the $45 you say you save with using Mobil gas.

mrgold35

I've been using Sam's Club gas for 5 years with my TSX and RDX and both vehicles meet or exceed the city/hwy mpgs. I even use Sam's gas when I travel out of town if they have it.

I've paid $3.46 for 91 at Sam's on Saturday, $3.31 about 5 days eariler, and $3.17 a few days before that. The other gas stations (shell, fina, conoco, Phillips 66, etc..) are charging $3.65-$3.75. I figure I save about $300-350 per year for both cars using Sam's Club compared to name brand.

The gas savings alone will pay for the yearly membership in a couple of months to costco and sams.

XLR8R

We are too far from a Costco or Sam's, but our grocery store offers .30 cents off per gallon of Sunoco, for the amount of groceries we buy. Usually saves about $5 per tank. Over the years, we have saved hundreds.

If they force through E15 though, I will take the hit and buy E10 or ethanol -free wherever I can.

Mr Marco

75% Shell, 24% Costco, 1% Other (out of convenience). I gave up on the thought of how much money I could save over here vs. over there because if you have to drive 5 miles out of your way to get gas that is 5 cents less expensive, you have actually spent 95 cents more to go fill up there.
If you are going shopping at Costco, sure, why not fill up. If you are driving home after work and go out of your way just for cheap gas, well you know what I think...
SAVE YOUR MONEY

russianDude

The best gas comes from stations that are using brand new fill-up machines and new tanks under ground. Those junky old stations usually have rust and crap, and you get your car choke up sometimes on bad gas. otherwise gas is gas, and 93 is 93 (unless some jackass dilutes it to 89 and sells it as 93).

EL_PIC

True.
The old tanks also leak and the ethanol soaks up water vapor and that lowers your octane, mpg, and increases corroding in your intake. Ethanol is an H2O magnet.
But 91 "premium" is watered down from the rich stuff of 93.
Anyone ever do a cost and mpg of 91 watered down "premium" vs 93 rich premium ???

terdonal

I have been using Costco gas for quite awhile now as it is on the way home and where we shop for groceries. The spread between others not what it used to be but still 10 cents per litre for premium. It still works out to a good savings over the period a year.

Worked fine when I had the RDX and still good on our ZDX.

Mr Marco

Acura recommends 91 octane in both of my cars, but they can run on 87..so,
87 vs. 91 octane... What's the difference???

--------------------------------------------------------------------------------

Lesson in Octane

Both levels will burn the same, no ascertainable difference in carbon buildup within the same brands. However, compare shell or chevron to an off brand and you can and will have more buildup w/ the off brand b/c they tend to have less detergents and poorer quality detergents in them.
As far as power goes, you probably won't feel the difference. If the engine was meant to run at its optimum on 91 octane and you put 87 in it, then it will simply retard the timing enough to prevent detonation. in doing so, you lose some power, but typically less than 3 or 4%. That’s about 6-8hp and for the everyday driver, you'll never feel the difference. However, you will more than likely have a decrease in your efficiency (MPG's) if you drop from a recommended 91 down to 87 due to the engine retarding the timing. This is more noticeable on automatics than on manual transmission equipped vehicles due to the downshifting at cruising speeds from the loss of the top end power.

Using my current mileage numbers and Oregon gas prices here is a quick & dirty calculation:

15 gallon use of fuel. 91 octane is $3.79 and 87 is $3.59 per gallon. AVG 17MPG with 93, but only 16MPG with 87.
Which grade is more economical to use?
-91 octane:
15 gallons * 17 MPG = 255 miles, 15 gallons * $3.79 = $56.85 to fill up
255 miles / $56.85 = 4.485 miles per dollar
-87 octane:
15 gallons * 16 MPG = 240 miles, 15 gallons * $3.59 = $53.85 to fill up
240 miles / $53.85 = 4.456 miles per dollar
It doesn’t look like much of a difference on the surface but add that up for somebody who drives 20k miles per year, and the difference is an whopping $580 per YEAR...

The reason Acura requires 91 octane is due to the high compression ratio of the engine. Higher ratios means that during the compression cycle, the piston moves in the upward direction so far that the air inside is compressed. Compression causes heat, and that heat can cause premature detonation of the fuel without the spark plug ever firing. This is detonation. The engine has a knock sensor and will detect pre-detonation conditions and will adjust engine timing accordingly to compensate.


If you have an older engine, you're more likely to get pinging (detonation). Why is that? It’s because older engines typically have some carbon buildup on the valves and on the piston head. Those carbon deposits can get heated to very high temperatures while the engine is running and will actually glow (think of charcoal in a grill). Those glowing embers will then ignite the fuel and cause detonation. Using a product like BG44K or Seafoam on a regular basis will remove the carbon deposits and therefore will reduce your chances of pinging.


Why does 91 not ping when 87 octane will? It’s in the octane rating. 91 is "harder to ignite" than 87. It doesn't burn any cleaner, or have more energy than 87 octane does. However, it requires more energy to initiate combustion, and therefore is less prone to detonation during the compression cycle or due to hot embers in the combustion chamber. Also, like mentioned before, 91 octane allows the engine to run at peak performance by allowing the timing to be as far advanced as possible.


On the contrary, for an engine designed to run on 87 and then you put 91 in it, you are simply wasting your money. The engine will still run the same and you won't notice a bit of difference in power or performance. Absolutely ZERO difference. As long as it is well maintained w/ low amounts of carbon deposits that would normally cause detonation and lead to a retarded timing, then using 91 octane won't do anything but make you poorer.

In Oregon the primary high octane gas in 92. If there is a difference between 91 and 93, it is the 45 percent rise in net income that Exxon will post this year.

Costco

It's anecdotal experience, yes, but when my friend ran Costco's 91 octane on his high-compression Integra, IIRC with the internals it was up to 11.5:1, his car pinged whenever he put in more than half-throttle. You probably won't notice going to and from work in a stock RDX, but if you have some modifications and a tune and you drive aggressively, I'd try a little bit first before you go all out with a full tank.

91 is the highest octane readily available around these parts if it matters.

As for my own name.... it's a long story but personally I don't fill up at Costco.

Mr Marco

^All bets are off when it comes to mods.