Optimal cruising MPG

I have been using 93 octane but this past fill up I accidentally used 91. Turns out premium at Wawa is 91 and Super is 93. I'll fill up with 93 next and redo the test. Only had one tank of 87 in it so far and that was from the dealer.
 
I have been using 93 octane but this past fill up I accidentally used 91. Turns out premium at Wawa is 91 and Super is 93. I'll fill up with 93 next and redo the test. Only had one tank of 87 in it so far and that was from the dealer.
There is a thread kicking around here where a couple of members mused that the timing adjustment made for higher octane might reduce the risk of oil dilution (fuel in the oil).
Others have poo-pooed that statement, then the pic of the torque curve comes out (which I don't think contributes one way or another to that theory, but I'm not a gear-head).

As I said, I track every tank and its mileage (manually calculated and computer) in a spreadsheet. Over time, the computer consistently tracks 1/2 MPG lower than manual calculations, but it's more consistent (it's not marred by imperfect fill-ups), so I use Calculated+0.5 as my measure. I can see I've lost a couple of MPG in the cold weather, assuming I'm not still in some kind of early-miles state of being (I'm at 7,000 on the odo).

I filled up today (and reset the trip odometer) and got stuck behind a guy who was doing the speed limit (jerk!) in a stretch of road I like to get crazy in. I noticed that the 10 mile trip home yielded 31 MPG!!! That's the most I've ever seen, even on my most conservative days. So this tank is a mission to see how much I can squeeze out.
 
I have been using 93 octane but this past fill up I accidentally used 91. Turns out premium at Wawa is 91 and Super is 93. I'll fill up with 93 next and redo the test. Only had one tank of 87 in it so far and that was from the dealer.

Shouldn't make any difference on the mileage unless you are really pushing the RPM.
 
Shouldn't make any difference on the mileage unless you are really pushing the RPM.
My understanding is that the engine has a knock sensor that perpetually adjusts timing. Would that not affect mileage? As you know, this is not like a regular engine where higher octanes makes no difference. And we're only talking about a 5% improvement.

I know that 93 octane yields greater HP at the higher RPMs, but I don't see why mileage would be improved in that scenario.
 
My understanding is that the engine has a knock sensor that perpetually adjusts timing. Would that not affect mileage? As you know, this is not like a regular engine where higher octanes makes no difference. And we're only talking about a 5% improvement.

I know that 93 octane yields greater HP at the higher RPMs, but I don't see why mileage would be improved in that scenario.
I'm basing that on the torque vs RPM curves people have posted for the turbo that shows they only diverge at high RPM and hence the 25 more horsepower only under those conditions.
 
Shouldn't make any difference on the mileage unless you are really pushing the RPM.
I too have also seen 5% better mpg results with 91octane vs 87 octane. 3 times I have done the experiment, Normal driving, ECO driving with no wringing out, and even tried wringing it out.

The first fill of 91 octane after a tank of 87 gets a small result.
The second fill of 91octane, on top of the 87/91 mix, gets a larger difference in the result. 2%
The third fill of the 91octane will result in a ~5% difference between the 87 tank and the third fill.

I believe in the scientific method, and I am as careful as I can to repeat the tests in like conditions and circumstances within reason.

My next test will be pouring a bottle of the 104+ octane booster from the auto parts store, and see what happens. I know this last method is cost prohibitive, but nevertheless, I am still interested in collecting the dataset.
 
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My understanding is that the engine has a knock sensor that perpetually adjusts timing. Would that not affect mileage? As you know, this is not like a regular engine where higher octanes makes no difference. And we're only talking about a 5% improvement.

I know that 93 octane yields greater HP at the higher RPMs, but I don't see why mileage would be improved in that scenario.

Mileage is improved because the engine running high octane and timing, uses less fuel to meet the same demand on power.
 
Mileage is improved because the engine running high octane and timing, uses less fuel to meet the same demand on power.
Exactly.

So...since the timing has been changed and less fuel is being consumed, do you have an opinion on those who think that high octane helps reduce the risk of oil dilution? They never really laid out an explanation, just that random thought.
 
Exactly.

So...since the timing has been changed and less fuel is being consumed, do you have an opinion on those who think that high octane helps reduce the risk of oil dilution? They never really laid out an explanation, just that random thought.
Sorry, but I have not read or seen enough on it to form an opinion.
 
I've noticed some differences in mpg.

There are places I can buy hi-octane gas without ethanol and I know it improves mpgs. I look on "pure gas.org"

Around here the best gas seems to be Shell premium- but it has ethanol. The octanes they sell here are lower (regular nolead is 84) because of the altitude and I think premium might only be 91, not 93. I can't say it delivers better mpg but I dont think it hurts.

I think I read the mixture might be richer burning regular so premium might create less soot.
 
I've noticed some differences in mpg.

There are places I can buy hi-octane gas without ethanol and I know it improves mpgs. I look on "pure gas.org"

Around here the best gas seems to be Shell premium- but it has ethanol. The octanes they sell here are lower (regular nolead is 84) because of the altitude and I think premium might only be 91, not 93. I can't say it delivers better mpg but I dont think it hurts.

I think I read the mixture might be richer burning regular so premium might create less soot.

I've not noticed any difference in mileage between brands...and I track the brand & location for each tank. The ethanol-free around me is far away and significantly more expensive that ethanol gas. Man, I wish we could get away from that program.

If you like Shell gas, check out this free program. You save a minimum of 5¢ per gallon on Shell gas, and up to 15¢ a gallon if you buy a couple of tanks per month (I think 2 tanks gets you that price). I was introduced to this via my AAA membership.
 
I don't get it...Turbo with Shell V Power Nitro+ 93, average highway speed is 72-75, and I *struggle* to reach 25 mpg. I'm gentle on the throttle, too. What gives?:confused:
 
I don't get it...Turbo with Shell V Power Nitro+ 93, average highway speed is 72-75, and I *struggle* to reach 25 mpg. I'm gentle on the throttle, too. What gives?:confused:
I'm the same way.

25MPG at those speeds is pretty good. I rarely get on a highway greater than 55MPH, and 23MPG is pretty much where I run on a routine basis, even when I'm gentle on the throttle. I've got 7,700 miles on my car and have never hit 25 on the computer mileage. I've had a few recent tanks where I've driven it hard, but most of them when I've been 100% conservative.

Personally, I think it has to do with atmospherics (temp, humidity, pressure), road surface-type friction for these specific tires, and goodness-knows-what-else.

I drove 12 miles to church this morning--37° out--and Fuel Monitor said 16.5 MPG.
I drove there this afternoon for an even--50° out--and got 24.5 MPG.

Exact same route.
Intentionally the exact same driving style.
No traffic to speak of here in the country, so that was not a factor.

We've had this conversation here before.
You'll not get an answer...there is none.
 
If I drive my CX-9 at 5 mpg above the speed limit (usually 45-55), on flat roads, I can get almost 30 mpg - over 140 miles. That is doing nothing but setting the cruise control at that speed. I live in a temperate climate - temps ~50f, but those figures are very easy to achieve.

For 12 miles at 37, you may never warm the car up to get decent mileage. Not sure why your MPG is so bad. I am averaging close to 24 MPG everywhere and that is in a car that is over 500 lbs more than your CX-5 (with the same engine).
 
dougal: I wonder if there's a gearing difference?

Although as you can see from Squidzilla's post (and the posts of others), I'm not the only Reserve guy with this "issue." As I said, there could be tons of factors, since many Reserve owners see mileage similar to yours.

And I wonder what other CX-9 owners experience.
 
My mpg mirrors Deer’s on 87 octane winter blend.Several 200 mile highway trips at 70-75 mph yields no more than 26 mpg.I am on my second tank of 91 non ethanol.Along with fresh Castrol edge 5w30 full synthetic i am curious to see if I can get those numbers up a bit.
 
dougal: I wonder if there's a gearing difference?

Although as you can see from Squidzilla's post (and the posts of others), I'm not the only Reserve guy with this "issue." As I said, there could be tons of factors, since many Reserve owners see mileage similar to yours.

And I wonder what other CX-9 owners experience.

That is a very good point.
 
I was really babying it with my last tank of 91 octane. Ended with ~26 MPG. I filled up with Costco 93 and I'll see how it goes this week. My plan is too see what the ultimate mileage in mixed driving is by accelerating slowly and maintaining the speed limit on the highways. As a comparison, my CRV is ~30 with normal mixed driving. I have come to close to 40 MPG on the highway portion of my commute going 65. The engine in the CRV is a 1.5 turbo vs the 2.5 turbo in the CX5. Big difference in size and performance.
 
Finished up first couple tanks on my new to me preowned 2019 GT. Both tanks averaged just over 30 mpg, right in line with what my wife sees on her 2018 Touring.
In every Mazda I've owned in recent years with the 2.5L (2016 Mazda 6 GT (I-eloop), 2018 CX5 Touring (CD), 2019 CX5 GT (CD)) we have always beaten the factory EPA numbers and surpassed EPA estimates.

The I-eloop equipped 2016 Mazda 6 was about 1-2 mpg better in my driving per tank versus the CX5's which have CD. (Mazda 6 was much lighter)

Personally I really like the Skyactive 2.5L NA engines, they have never given us problems and deliver acceptable performance and gas mileage.

On the highway I stick to speed limit or +5mph if traffic is really flying. 65-70. Gas mileage really soars if you have 55mph highway stretches.....that's when CD is kicking in and bumping up the fuel efficiency.
 
Just my 2 cents with my GT-R. I can hit 30mpg cruising around 60-65 no problem. Minor increases in speed above that make mileage plummet, which you would expect. During my regular 9 mile each way commute, I get about 24 on the way in and around 20 on the way home when there's more traffic. But I live in a smaller city, about 170k. I never baby it to try to get great mileage but I rarely floor it either.
 
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