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Car Corner
Mileage  

April 1, 2002
By Scott Lewis

This month I want to talk about something that few car enthusiast talk about. Mileage. I plan to discuss driving for mileage, as well as how the price of different qualities of gas can impact your mileage and the cost to consider. Finally, I will take a look at what it really costs to make the switch to getting really good gas mileage.

85 Miles Per Day

Back in October I started working for a company that increased my daily commute to 85 miles per day. Ouch! This is a huge increase to the less than 20 miles per day I was doing before. Add to that that I am now driving 5 days a week to work instead of 4. More Ouch. I put about 10,000 miles on my car in the first 5 months at this job.

I used to have a low mileage Camaro. It is a 93 Z-28 that had only 60,000 miles prior to October 2001. My wife and I put 34,000 of those miles on it in its first 36 months (March 93 - March 96). At that time my wife got a Ford Explorer and that became the family car. In 96 my Camaro started living a pampered life. I put about 26,000 miles on the car over 5-1/2 years (March 96 - September 01). That's an average of less than 5,000 miles a year. Not bad. I fully expected this car to last a very long time as a low mileage car.

Not anymore. I am on target to put over 20K miles a year on the car. I will be over 100,000 miles sometime in 2003. Like the saying goes, "best laid plans of mice and men..."

That bring us to the topic of this article. Mileage. I decided to take the time to see how driving style could effect my gas mileage. I have long thought I was better at squeezing out mileage from a car than the EPA. I was able to get a high of 38.5 mpg out of my 89 Honda CRX with a EPA highway rating of 33. Not bad. I had hoped to do something similar with the Camaro, which is EPA rated at 23 mpg on the highway.

The Plan

For each of three tanks of gas I was going to use three different driving techniques. First would be a maximum mileage driving style. This is the style of driving that I used to get 38+ mpg out of my CRX. It uses some information I acquired a very long time ago. If you really want to know my technique drop me a note and I will tell you how to do it.

Second would be a tank full of driving with no regard for mileage what so ever. This is supposed to be the worse-case scenario. The third case would involve using cruise control. Many people typically believe they will get better mileage using cruise control. I was pretty sure I could beat it.

Here were the results of those three tanks of gas:

1) Driving for mileage... 19.6
2) Driving NOT for mileage... 19.7
3) Using Cruise Control... 17.4

Wait a minute. Why did I get better gas mileage romping on the gas like a maniac for three days straight? Well, a strange think happened in the middle of my testing. After the first tank the price of gasoline dropped a LOT. I was able to buy the "good stuff" for less than the "middle stuff." I usually put 89 octane gasoline in my car, treating it to the supreme grade (93 octane here in San Antonio, sorry you California car nuts) once in a while. When the price dropped so drastically in October I started using the premium grade gas all the time.

So to even the score I did another tank of gas using my technique for good gas mileage. Here are the final results showing the grade of gasoline for each test.

Type of Driving       Octane    Mileage
Driving for mileage   89        19.6
Zooming Around        93        19.7
Cruise Control        93        17.4
Driving for Mileage   93        21.6

What have we learned? If you drive with a mind on mileage you can make a difference. Also, we find that cruise control sucks for getting good mileage. It is better at preventing you from getting a ticket though. 

We also learned that some cars (maybe lots of cars) get better gas mileage when you put better gas in them. Why? My theory is that modern performance engines have knock sensors to determine when damaging detonation is just starting to occur. The on-board computer will adjust the timing to prevent the detonation (or knock, where the name of the sensor comes from). This adjustment diminishes the cars optimum settings for both performance and mileage. Running good gas gets the most out of the engine... a significant amount.

Mileage vs. Cost

Does the mileage gained by using better gas justify the cost? At the time I made the switch the cost of Premium gas was around $1.10 (yea, $1.099, I will not get into that). At this rate it was about 8 to 10 cents more expensive that the middle 89 octane gas.

Let's do some math. To get a real handle on this we need to start calculating miles per dollar (mpg) instead of mile per gallon (mpg). Let's start with our $1.10 per gallon. We get 21.6 mpg by taking the length of the drive (218 miles in this case) divided by the number of gallons used (10.1) That gives 21.6 (rounded). I paid $1.10 for the gas, so it was $11.11. Applied to the 218 miles I got 19.6 miles per dollar.

Let's assume for a moment that 89 octane gas is 10 cents cheaper. We will use the number from my 89 octane trip (295 miles / 15.0 gallons = 19.6 mpg). If we assume that I paid $1.00 for that gas then that works out to 19.6 miles per dollar, as well). A tie.

Or is it. We had different length drives. Let's use hypothetical numbers, and stretch this out for a longer distance. We'll assume a full week of driving (85 miles a day x 5 days = 425 miles). As I write this prices are on the rise again. Let's go for $1.25 for 89 octane gas, and $1.35 for 93 octane gas.

Gas    Miles    Gal. Needed    Price    Total Cost
93     425      19.7           $1.35    $26.60
89     425      21.7           $1.25    $27.13

So paying more for better gas actually saves money. However, this is a percentage difference. Notice that I am getting approximately 10% better gas mileage. So the difference in the cost of the gas would have to be more than 10% for it to be cost effective to use the 89 octane gas. This only happens when the price is very close to a dollar, and at that point I was willing to spend the extra money for "the good stuff."

You need to perform this on your own, but it is my belief that my results are close to what many cars (especially ones with performance oriented engines) will show. Try it out for yourself and let me know. You need to be consistent. When I did my testing I gassed up the car at the same gas station, at the same pump, at the same middle pumping speed on the handle, and didn't "squeeze" more into the car when the pump handle kicked off. I was also very consistent with my driving.

Beating the EPA

Notice that I said this car was EPA rated at 23 mpg on the highway. I do most of my driving on the highway now. Before I started working at this job, on the day I drove up to accept the offer. I did a single round trip from the gas station to work, and back to the gas station. It was 72 miles and used exactly 3 gallons of gas 23.7 mpg. Better than the EPA rating, but not by much. After that I did a full tune up on my car and added a cold air induction box. The old air filter was so clogged that I thought I had to see better gas mileage. Unfortunately, I also added wider tires and wheels at that time. By increasing the tread width I have increased rolling resistance, and in turn reduced my gas mileage. I suspect I am losing almost 2 mpg to those tires. But I don't have the time or resources to test that.

Buying Good Gas Mileage

When I took this job I actually thought about buying a car that got better gas mileage. Could I save enough money on gas to justify a car that got better gas mileage. I mostly drive like normal, and I am averaging just a hair under 20 mpg. What would it take to make the difference? Let's do some more math. We will assume a cost of $1.35 for gas, and assume 4 weeks in a month.

Car       Payment   Miles   Mileage   Gas Cost   Monthly Cost
93 Z-28   $0        425     20        $114.75    $114.75
Econobox  $250      425     40        $57.38     $307.38
 

Even if I could cut my month gas bill in half, I can't afford a new car with the savings. For fun I wanted to take this to the next step. How much money can you save if you could buy a car that gets better gas mileage when you buy your next car. Image we live in this utopian world that says for an extra $5000 the car you buy will get 100 mpg. Wow, that should be worth it. Let's see. For the following we don't want to muddy things with such trivia as interest... this utopian world still has 0% financing, and we assume a 5 year loan with no money down.

Price    Payment   Miles   Mileage   Gas Cost   Monthly Cost
$20,000  $333.33   425     30        $76.50     $409.83
$25,000  $416.66   425     100       $22.95     $439.61

See, it still doesn't pay. Trust me it would cost at least $5,000 more for a car that could get 100 mpg... but why bother when it will not pay for itself... ever! I love this kind of math. This is why the manufactures aren't building ultra high mileage cars... not because it is not possible, but because nobody wants to eat the cost to get there.

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