Premium vs. Regular Fuel: THE ANSWER

[Matt4949]

So since I've bought my Pathfinder a couple months ago, I've really been let down by the gas mileage. Locating any kind of specific info on what fuel I should use was surprisingly impossible, so I decided to run a little experiment and record my mileage first using regular 87 octane, then by running the "recommended" premium 93 octane (HOORAY CT). In the interest of keeping the figures represented here accurate, I would fill the tank when the gas light came on, only at Mobil or Shell, without topping off, approximately 18 gallons. Additionally, I made an effort to keep my driving consistent, 95% highway to work (cruise control at 62mph) and minimal city driving. Since I have bought the truck, I don't think she's seen 3k rpms. Now before anybody wants to jump down my throat, I realize there are many other variables that could have altered these numbers, especially with all the snow we got in the past few weeks, but I figured this process would give me at least ball park areas to make a more educated decision. Now bear in mind we still have that winter mix in the Northeast and I'd expect these figures to rise some in the summer.

Using the equation: miles traveled per tank / price to fill tank = miles traveled per dollar
Figures rounded to .100 where applicable

Regular Fuel 87 Octane; Current Price: $3.81
18 gallons * $3.81 = $68.58 Price to Fill

242.5 miles / $68.58 = 3.536 m/$
254.1 miles / $68.58 = 3.705 m/$
247.6 miles / $68.58 = 3.610 m/$
256.9 miles / $68.58 = 3.746 m/$
Average: 3.649 miles per dollar

242.5 miles / 18 gallons = 13.472 mpg
254.1 miles / 18 gallons = 14.117 mpg
247.6 miles / 18 gallons = 13.756 mpg
256.9 miles / 18 gallons = 14.272 mpg
Average: 13.904 miles per gallon


It is also worth noting that I waited a few tanks in between to allow the knock sensor to adjust to running the premium fuel. (Much thanks to Chuck Tribolet!)

Premium Fuel 93 Octane; Current Price: $4.11
18 gallons * $4.11 = $73.98 Price to Fill

262.4 miles / $73.98 = 3.547 m/$
261.6 miles / $73.98 = 3.536 m/$
256.3 miles / $73.98 = 3.464 m/$
260.7 miles / $73.98 = 3.524 m/$
261.2 miles / $73.98 = 3.531 m/$
Average: 3.520 miles per dollar

262.4 miles / 18 gallons = 14.578 mpg
261.6 miles / 18 gallons = 14.533 mpg
256.3 miles / 18 gallons = 14.239 mpg
260.7 miles / 18 gallons = 14.483 mpg
261.2 miles / 18 gallons = 14.511 mpg
Average: 14.469 miles per gallon

So taking a look at these numbers broken down, we can see that although you most certainly get worse fuel efficiency running regular fuel versus the premium, you in fact are spending less money to drive any given amount of miles (albeit the actual difference is minimal) on the regular octane. With that being said, my truck has 119,000 miles on it now, and I will continue to run the recommended premium fuel. This is because I find the actual amount of difference in miles per tank (about 9) and cost to fill (about $5) to be negligible. Also, and here's the key reason why recommended is no longer in quotation marks, when running the regular fuel that VQ felt like a tired old engine with 100k+ miles on it. However with that premium fuel, she feels light on her feet and peppy from a stop. Personally, after driving with both fuels back to back, the difference is incomparable.

This summer I'm planning to do a full tune-up as well as possibly a CAI to try to bump these numbers, but obviously I will strictly be running the premium fuel at that point. Thanks for reading! Hope it helps some who were unsure about what fuel to use like me.

[dpassino]

Great Write Up! Very informative, will look forward to seeing your summer write up! With my old Maxima, mind you I wasn't as consistent with driving patterns, but there seemed to be a good 20 mile difference on a full tank with Premium being the winner, not to mention the pep on her (165,00mi.)

The pathfinder is a gas chugging beast though, but I love her.

[PathyConvert]

What year is your Pathfinder? I'm getting much better fuel economy from my 2004 Pathy, and that's even during our cold Canadian winters, which drives fuel economy into the basement!

Keep in mind that my Pathy has a very low odometer reading. I only have 53,000 km (or 32,932 miles)! It was my mother-in-law's truck, and she hardly drove it!

I've been averaging 13.72L/100Km (or 17.15MPG) in mixed approx. 50/50 city/highway driving. That is with 87 octane gas. I plan to keep a close eye on my fuel economy and will do more testing with 89, 91, and 94 octane.

Great write-up on your part, very thorough!

[Matt4949]

PathyConvert,
Thanks for the kind words. My Pathy is a 2001 LE 3.5.

In truth, when using the 18 gallons per fill up I did round up and obviously it was not a consistent fill every time. Additionally, if I were to round that figure down to 17 gallons, my mpg would rise approximately 1.

My main goal in this experiment was to use consistent figures to test the efficiency of the fuels, rather than the final figures for actual mileage. I expect in a more accurate test for these figures to rise.

That being said, good luck with your low-mileage Pathy. I'm envious of your fuel economy. Hopefully I'll be able to get up there after the tune-up!

[pathy001]

Cool study!! I think I'm in the same boat as you .... getting around 13-14mpg.

A couple thoughts: to be more accurate you should have calculated mpg per tank of gas. To do this... fill up the tank and reset your trip odometer. Next time you get gas, fill it up again and note the gallons you put in and not the miles on your trip odometer. This will give you more accurate numbers. YOu can always put in an "average" cost of fuel but you'll be able to see the difference and your numbers will be more precise.

[john12121]

Thanks a lot taking the time to write this post..I read it it was extremely helpful. I was always thinking which one is best for my car..But now I know that premium is the best choice..

[festerfm]

i usually run 89 octane in my 02. it is a 5spd 4wd with 120k miles. i live in a pretty rural area that is rather hilly in northeast pa. the last 3 months or so, i have been averaging between 17.5 and 19 mpg. that is with me filling the tank every time, not an attendant. that includes some full throttle fun once in a while but mostly just normal commuting. 2 weeks ago i did a 175 mile round trip to a volleyball tournament with me and 4 others in the car plus all the shoes, bags, tents and what not.. averaged on that trip 21.4mpg. only mods done is a newer high flow muffler and an intake. seems pretty decent to me.. i was expecting between 15-17mpg on average..