Does 89 octane save, and is 93 octane even better?

Tacoma-Robert

Tacoma-Robert

Well-Known Member
I had been running 89 octane gasoline in my new 2013, 4 cyl, tacoma. Got about 18 mpg with mixed driving.

Decided to save some money and use 87 octane, instead of 89.

I then noticed that my mileage probably decreased about 1 mpg. It seemed to drop from 18mpg to 17mpg.

I say probably because I only ran a couple tanks of it. Can anyone confirm or contradict this finding?

If that's correct, then the 87 octane caused two problems. i) Cost me more money, instead of less. and ii) caused me inconvenience.

Here's why. With 89 octane I got about 324 miles before I felt like filling up with another 18 gallons (324 miles = 18 gallons x 18mpg). If it's $3.50 per gallon, then that's a cost of $63.00.

But with 87 octane I only got about 17 mpg. So that's only 306 miles (306 miles = 18 gallons x 17mpg). But 87 cost about a dime less than 89 ... so .... if 87 octane is $3.40 a gallon, then that's a cost of $61.20.

Thus, I saved $1.80 to buy 18 gallons of 87 instead of 18 gallons of 89.

And traveled 18 fewer miles (324 miles - 306 miles).

But, wait, to go the same distance, I'll need to buy more 87 octane to drive 18 extra miles to match the same distance as 89 octane. At 17 mpg for the 87, that means I'll need to buy an extra 1.1 gallons of 87 octane. (18 miles / 17 mpg). That's an extra $ 3.60. ($3.40 x 1.1 gallons).

So, 87 octane cost me a net total of $1.80 more ($3.60 - $1.80) since I had to buy more of it to travel the same distance, but it cost less per gallon.

More importantly, 89 octane is more convenient since I need to fill up less often. On the highway with higher mpg's this could really be significant!

Question 1: Is my math ok?

Question 2: Do you all see a difference in mileage between 87 and 89?

Question 3: Does it hurt the truck to run 93 octane? It's another 10 cents a gallon, but what the heck? Perhaps it's even less expensive and even more convenient?
 
Yota4life said:
Are you a math teacher or something?haha you just blew my mind
Click to expand...

LOL! I was actually a math assistant, up to calculus level, back in college a million years ago.

But it's MY FAULT that you don't understand. My explanation was very very very poor and needlessly complex.

It sort of boiled down to this ...

If I buy cheaper gas, then I need to buy more of it to go the same distance.

In other words, I paid $3.40 per gallon instead of $3.50 per gallon. So that savings saved me $1.80 at fill up ...

but ... since the cheaper gas gave less mileage, then I had to pay $3.40 for one extra gallon to go the same distance.

I don't know? Even that explanation is sort of weak. I'm out of practice.
 
Tacoma-Robert said:
LOL! I was actually a math assistant, up to calculus level, back in college a million years ago.

But it's MY FAULT that you don't understand. My explanation was very very very poor and needlessly complex.

It sort of boiled down to this ...

If I buy cheaper gas, then I need to buy more of it to go the same distance.

In other words, I paid $3.40 per gallon instead of $3.50 per gallon. So that savings saved me $1.80 at fill up ...

but ... since the cheaper gas gave less mileage, then I had to pay $3.40 for one extra gallon to go the same distance.

I don't know? Even that explanation is sort of weak. I'm out of practice.
Click to expand...

It's alright, I understand it now cause I'm actually awake and focused. I just woke up when I read it and was like huh? You don't sound out of practice to me I that helps. Haha
 
whippersnapper02 said:
I saw no change running higher octane in my truck.
Click to expand...

It really did seem to do better with the 89. Even as soon as the first quarter of a tank I noticed that it seemed to be getting fewer miles. But I'm not sure at all.

I wish this truck had an mpg gauge. Crying out loud. No heated mirrors and no mpg gauge.

I always noticed better mpg when I used better gas in my previous ride, which was a Honda Accord. Sometimes it could be only from a better brand. But that car seemed to be very sensitive to the fuel quality.

My biggest goal is to get longer range. I'm so used to going 450 miles on a tank of gas. 350 is annoying.

But I love this truck. It's worth it. The Accord was one of the worst cars I ever owned, in my personal opinion. So glad to be rid of it.
 
This is fun. I am wondering what the mileage improvement would have to be to break even on cost? Let's say that the

87 octane gas gave me 17 mpg.
87 octane gas cost $3.40 / gallon.
89 octane gas cost $3.50 / gallon.

cost = $/gal * gallons

gallons = miles / mpg

thus: cost = $/gal * miles / mpg

for the two gasolines X & Y to be equal cost then

$/gal * distance / X mpg = $/gal * distance / Y mpg

let Y be the cheaper gas ...

substituting: $3.50/gal * 400 miles / X mpg = $3.40/gal * 400 miles / Y mpg

Thus: 1400 $miles/gal / X mpg = 1360 $miles/gal / Y mpg

Thus: Y * 1.03 = X

Thus if Y is 17 mpg then: X has to be 17.5 mpg

In conclusion, for these pump prices, in order to break even on the cost of 89 octane gas, then 89 octane has to give 17.5 mpg, if the 87 octane gives 17 mpg.

Hey, just playing. I'm not even checking anything. Anyone sees anything wrong it won't hurt my feelings.

Just having fun. Goofing around.
 
Another way to do it would be to figure fuel cost per mile. For instance, yesterday I filled my truck up with 93 octane fuel and drove to Dallas. When I figured up my tank mileage, I got 24.7, which is a new high. So divide 3.369 (cost of a gallon of fuel) by 24.7 (miles driven on a gallon of fuel ) for a cost of approximately 13.63 cents per mile. My previous best was 22.4 and gas cost was 3.069, which comes out to 13.7 cents. In all honesty, the sample is much too low. As I drove to Dallas I had a big tailwind and drove lass than 50 mph because of road work for about 30 miles. But it's enough to make me want to continue the experiment awhile longer.
 
I just filled up yesterday and I calculate all my tanks and I keep getting 14s and yesterday I got 15mpg. FML
 
Here's something you might not know. I live in Canada and travel to the USA lots. When I buy the same 87oc in the USA I average 1-2 extra miles per gallon more then my Canadian gas? Why? I think it's the additives.
 
Maybe, but both have 10% ethanol in the gas. It's just crazy because you can really notice the difference just by driving.
 
I don't know if this will help any. I used to fill up with 89 but after finding out that when they fill the tanks at the gas station any left over from the truck goes into the next tank. Meaning they fill 87 and the left over goes into the 89. So why pay for 89(not that it's a big difference) if your getting 87.
 
Pure gas is the only thing that gave me better mileage. Octane rating never really matters much to me except in the summer when it's really hot. I usually run a little higher octane because my truck seems to knock in hot weather.
 
Demo Man said:
I don't know if this will help any. I used to fill up with 89 but after finding out that when they fill the tanks at the gas station any left over from the truck goes into the next tank. Meaning they fill 87 and the left over goes into the 89. So why pay for 89(not that it's a big difference) if your getting 87.
Click to expand...

I have personally experienced what you are saying on many occasions. Sometimes I can fill up and do great with 87. Other times it just feels like 87. Guess it depends on how much 89 or 93 they have to 'spill down' - so to speak.

It can work the other way, too. I typically trust Shell gas. But one Shell dealer in my area I think isn't filling their pumps with Shell gas. I got some tanks that were so bad that my car was knocking all over the place with 89 octane! One day I drove by and they were filling their tanks from a gas truck that looked like it was from some war zone. I'll bet $20 that they weren't selling Shell gas, although they had the logo all over the place! Started going somewhere else and my car ran like a champ afterwords. Haven't been back to that particular station since.

Otherwise, I play the odds so to speak, and my best results have been to stick with gasolines that have passed some minimum standards. Here's one source of info to look at ...

http://www.toptiergas.com/retailers.html
 
Well, today I filled up with 93 octane! :shifty:

Wow! I'm serious. Could 'feel' a difference a couple blocks down the road.

At the first quarter tank mark on my fuel gauge I had driven 160 miles on the 93 octane. In the past I have usually gotten about 100 miles at that point. Dare I hope?

Using Exxon gas. That's all I've been using since I bought the truck in December.

I know. I know. No need to say it. A sample of one probably means nothing.

Now, according to my math, I only need 1 mpg improvement to break even on the cost of the extra $0.20 per gallon.

Hardly a legitimate study. I'm only curious and not married to the theory. But I am keeping my fingers crossed and having fun with it.
 
Last edited:
I've never had a problem with 87 either. I have certain gas stations I stay away from only due to the fact that my truck doesn't like their fuel.
 
You must log in or register to reply here.
Back
Top