Author Topic: Gasoline Calculations  (Read 2468 times)

Offline scuzzy

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Gasoline Calculations
« on: Jul 29, 2011, 04:41 PM »
My primary car is an all wheel drive 2006 Subaru Legacy GT that I bought some 2-1/2 years ago. It is a very fun car to drive and it has an awesome stereo system. The power plant is a factory turbo charged, flat 4-cylinder engine that cranks out around 250-HP. The setback to this fun-to-drive car is that the fuel mileage is less than desirable and it "requires" premium fuel.

With the price of gas reaming us, I was forced to make some adjustments to my driving habits in order to preserve fuel. I researched the lowest grade of fuel that I could use that would not harm the engine. Diehards were adamant that the only fuel I should even consider is premium. However, lots of people have successfully used mid-grade without modifications and no harm befell their engines. My local Subaru dealership confirmed that I could use mid-grade without losing my 100K mile warranty. They also admitted that they only use regular unleaded on all their vehicles, including their "GT" demos without problems.

I switched over to mid-grade and carefully monitored the performance of my car. That change automatically saved me 10 to 15 cents per gallon, depending on where I filled up. I have been using mid-grade for over a year and I can honestly say I never noticed the slightest difference in performance. Someday I might take it down to regular grade and see if there's an effect, but for now I'll keep using mid-grade.

But as I started paying $4.00+ per gallon, I decided to make further changes to my driving habits. Several months ago I became much more thoughtful of how often I drove the car. Wherever possible, I either did not make the trip, went with someone else, or simply combined all of my errands into a single day or trip. This change alone greatly reduced my trips to the fuel pump. But that still wasn't enough. I was keenly aware that my driving habits needed an adjustment. So I forced myself to stay off the turbo and to keep a maximum speed of 65 MPH on the freeway. It's now been about 4 or 5 months since I made that change, and my average fuel mileage jumped from 21 MPG to 26 MPG. This is a consistent average that I can confirm over the last several months.

I had an old gasoline calculator that I created in Excel some years ago to compare MPGs between "Vehicle A" and "Vehicle B". The calculator was designed to compare the cost at the pump over hundreds and thousands of miles. I used the same calculator to determine how much money I'm saving by increasing my mileage a measly 5 MPGs. It was quite an eye opener. Veh A is my Subaru at 21 MPG, and Veh B is my Subaru at 26 MPG.

On average, I currently drive around 350 miles between fill ups (about once a week). With the current cost of mid-grade in my area (about $3.50 per gallon), I'm saving an average of 3.2 gallons of gas per 350 miles, which comes out to $11.22 per fill up! With a fill up of 13.5 gallons, this is equivalent to saving 26 cents per gallon. Over a year (adding 3,000+ miles for family visits, etc.) my fuel savings for the increase in MPGs alone is $673.08. That's a chunk of change, Folks. The savings is actually much higher when considering switching to a lower grade fuel and reducing unneeded trips.

These adjustments have positive side effects besides spending less on gasoline. To begin with, driving on the Interstate in the right lane at 65 MPH is relaxing. Before, I was constantly speeding up and slowing down, passing and being passed, and stressing over other fools on the highway. You know the song. Now, I mostly just stay in the right lane and I don't worry about it. It's not often that I have to pass anyone, and then I only do so when I have plenty of space and time to get around the car. Driving slower also puts much less wear and tear on the car, especially the tires and brakes.

Click the photo to see my simple calculator (PM me if you want the Excel file emailed to you for your own use):

Offline Bill

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Re: Gasoline Calculations
« Reply #1 on: Jul 30, 2011, 07:36 AM »
What's the Interstate speed limit, if there is one.  I have been on roads around Salt Lake City where there were no limits.

Bill
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Offline scuzzy

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Re: Gasoline Calculations
« Reply #2 on: Jul 30, 2011, 10:39 AM »
The speed limit in Colorado is 75 MPH. Most people around here seem to think it's closer to 85 MPH.

Offline Bill

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Re: Gasoline Calculations
« Reply #3 on: Jul 30, 2011, 10:42 AM »
People would be the same if it was 45 or 95.  But thanks for the info.

Bill
Fractal Design R5 | Asus  Z170 Pro | Intel i5 6600k | 16 GB G.Skill Ripjaws  DDR4 2133 | Seasonic 650w PSU | eVGA GTX 550 TI | Samsung 960 M2 500 GB | Samsung 850 EVO 500 GB | ASUS Burner | Windows 7 64-bit

Offline Ace

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Re: Gasoline Calculations
« Reply #4 on: Jul 30, 2011, 11:03 AM »
Well, as usual, I think you missed the boat.  I don't know if it's even an outboard Johnson or Mercury, or some inboard Chris-Craft type thing.

First off, it's obvious the faster you drive the less time the trip takes and the less gas you use.  You get that thing up to 120 or so, and maybe convert it to nitro or at least add one of those cans of fuel injector cleaner or STP and see how quick the trip goes.  Well, unless somebody like you stops you, but still you turn off the car when you get pulled over so I don't see that as detrimental to your mileage, so much as your cash flow.

Also, if you want to get real gas savings, consider a trailer hitch.  But put it on the front.  Then, get a friend or at least somebody agreeable to drive in front of you and tow you.  You can really sit back then and enjoy the ride; heck, you could even nap during the trip rather than when it's over. 

Ace; just make sure you're not in "park" when you guys take off.

Offline scuzzy

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Re: Gasoline Calculations
« Reply #5 on: Jul 30, 2011, 11:28 AM »
Well of course.

You reminded me of a traffic stop I did last year. The woman was driving like an out of control maniac on steroids. When I stopped her, she was pushing 50 in a 30. You'd a thought she was driving the Winston 500 through the local hood. Her excuse was that she was running out of gas and needed to get to a gas station right away. When I looked at her dash I could see that the orange gas warning light was on.

Yes, I gave her a ticket.

Scuzzy; Ich liebe dich nicht du liebst mich nicht.

Offline Ace

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Re: Gasoline Calculations
« Reply #6 on: Jul 30, 2011, 12:02 PM »
Yeah, but; if you're going fast enough you can coast to the station, even if you run off.  Like those ideas of shutting off your car and throwing it into neutral heading downhill. 

I'm not coordinated, though.  I can heel and toe an old Mercury Topaz that tends to die if you don't push the idle, hopping between the brake and gas and both.  But it's like patting Pat and rubbing your stomach at the same time; you get confused and you've got trouble.

I've done dumb stuff, like locking myself out of my car, but I have never run out of gas.  I figure there's a way to head that off.

Ace; you shoulda shot out her tires after the ticket.  Do they ever race down Pike's Peak?  Does the Monster win that?