Mystified

It's been a very frustrating period. Over the last few weeks, my five tank moving average mileage has decreased by more than two miles per gallon. The troubles began with the brake job reported in an earlier post. The pads definitely dragged on the rotors for a few hundred miles after that - I could feel it in the behavior on coasting to a stop and, in the beginning, I could smell the burning pads. But these are no longer the case. The car rolls just like it always has, the highway instant miles per gallon seems normal, and yet my mileage has deteriorated. Why?



I got involved in an argument with a guy who has a blog called "mental radiation." (Note that that link is to the argument, I believe he actually maintains his blog at a wordpress site here.) The nature of the argument was over the extent to which the use of ethanol as a motor fuel eliminates the impact of driving on fossil fuel usage. As is common in internet arguments, neither of us was convinced. But in the process of our discussion, he looked at my blog and made several comments.



One of them was in response to my posting about my learning curve, in which I opined that the increasing trend in my mileage, as shown by the five and ten tank moving averages, indicated that I was learning to better maximize fuel efficiency. Bill Anderson, publisher of "mental radiation," was skeptical. His belief is that there are likely other reasons, e.g., different brands and different seasonal blends. I'm beginning to wonder.



I've bought Chevron, mostly from the same station, for the duration of the experiment. There have been perhaps three exceptions when I patronized Arco. The Arco purchases are not distinguishable on the graphs or in the raw data, but the downward trend from the last few weeks is obvious. I don't know if there has been a change in gasoline blends in June and July, certainly I haven't read of one. Maybe something's wrong with the vehicle. But even at that, why does my highway instant mileage still indicate what it did when my trend was upward?

$4.85 per gallon

Today I paid $4.85 per gallon for fuel. It was a very painful fillup since I needed almost 40 gallons. In context, that means I had used about 3/8 of a the fuel in my tanks. I mentioned in an earlier post that I'm a pilot, and I'm referring to the fuel in my airplane.



Because much less "avgas" is refined as contrasted with the vast quantities of automobile fuel, avgas is more expensive. My particular airplane, a Piper Saratoga, cruises at about 168 knots (193 statute miles per hour) while burning about 18 gallons of fuel per hour. That works out to about 10.7 statute miles per gallon.



I took it out for some "pattern work," that is, executing touch and go landings for the purpose of staying sharp and probably burned about 10 gallons or so. In light of my extraordinary efforts to save an ounce of gasoline here and a teaspoon there, how does my flying fit in?



It certainly enables me to accomplish things I otherwise couldn't. For example, I have an employee in the field, working a project in Fresno. He will work Sunday night until about 6am Monday morning and needs to be back at our office in Long Beach by 9am. This could not be accomplished without the airplane, but the cost of doing it will be about $500.00. That figure values my time at zero (which many who know me say is appropriate).



But in the end, I really do it because I like it. What will my breaking point be? I'm not sure yet but I know it's out there somewhere. The aiplane holds 102 gallons of fuel, and I was told by someone that avgas is going for $6.25 per gallon in Las Vegas. When I fly there, I burn around 25 gallons each way, so figuring half the trip at $4.85 Long beach prices and half at $6.25 Vegas prices, the fuel for that trip costs about $280.00. That's a steep price if I fly alone. The airplane has six seats. It's really only comfortable for four, though I've had as many as five. But with four, including me, that's $70.00 per person. Of course, being a private pilot, not commercial, I can't charge my passengers. They're allowed by regulations to share the cost, however.



Now, I can fly at a considerably more efficient airspeed and use less fuel to make the trip, but you get an airplane to GO FAST and it's beyond my tolerance to pull the power back and cruise at 120 knots (138 statute miles/hour)to save fuel. To drive there and back using my current technique would use 20 gallons and cost something like $65.00. I could take the same three passengers and make the round trip for a little over $16.00 apiece, leaving everyone an extra picture of Ulysses S. Grant for the tables, should they be so inclined. That trip would take not quite 5 1/2 hours each way and would be a major test of my passengers' patience.



I am currently projecting that, in the year following the start of my driving experiment, I'll use 884 gallons of automobile gasoline. Had I used my pre-experiment driving techniques, I estimate I would use about 1310 gallons in the same time. I estimate that I use about 1,080 gallons of avgas per year.



I guess my flying negates any ability I might have thought I had to brag about diminishing my use of fossil fuel or my "carbon footprint." Still, at the end of the year I will have saved 426 gallons of auto gas. That's better than if I hadn't done it.

Frustration

Two weeks ago, I took my Jeep in for some brake work. I patronized the place to which my company takes its vehicles (we have a fleet of about 28) for service. When it was returned, I was told that they had had to replace the rotors because they had gotten too thin (after about 134,000 miles) as well as the pads. The mechanic told me to go easy on it for a hundred miles or so to give the rotors and pads a chance to set. Little did he know - what he would think of as going easy would be insanely abusive to me these days.



But as I drove, the smell of burning brakes suffused the cabin. I could feel the brakes grab as I would attempt to coast to a stop. The instant mileage indication was at about 60% of what I had come to expect in any particular driving situation. OH NO!!! I'm burning fossil fuel to heat metal for no reason. My five tank moving average had been at 24.23 m.p.g, and my last two tanks were 21.98 and 20.36 m.p.g. The bottom line is that I'M WASTING GASOLINE! I was so horrified that I took the Jeep to the dealer to have them make sure the installation was performed properly. They confirmed that it had been and verified that, even after 400 miles, the symptoms I was experiencing were not unusual.



I believe that it's over now - when I let the car coast I feel no resistance and the numbers seem to be back where they should be on the display. But I now realize how sensitive I have become to the behavior of the car. Even after the smell of the brakes was gone and the car was close to being back to normal, I could tell it wasn't quite right. I'm conscious of every aspect of its behaviour by both feel and by the numbers. I think if there were problems with fuel injectors, spark plugs, etc. I would be able to quickly sense and remedy them.



Now it's back to trying to get the averages to 25 m.p.g. It's starting to look like that's the practical limit for this car. I'm going to change the air filter to a more nonrestrictive after market type (Air Hog or something) to see if that has a measureable effect. My IT guy is very interested in that experiment but I had to wait until the Great Brake Job Catastrophe had abated.

Economic choices

The other day I stopped at the bank to get some cash. The particular branch I chose to patronize had a drive through window, and I watched the action for a few minutes. I saw a Hummer (H2) use the window and it set me to thinking about the motivation.



In an earlier post I gave some fairly detailed estimates of the consequences of drive through windows, estimating that if they all went away we could save about 350,000 barrels of oil per year. Clearly, this is not a huge amount. What about the Hummer pilot?



The engine is a 6.0 liter V8. My Grand Cherokee has a 4.8 liter V8 and uses about 0.38 gallons per hour at idle. It seems very reasonable to assume that fuel consumption at idle is directly proportional to engine displacement so I'll estimate that the H2 uses (6.0/4.8)*0.38=0.475 gallons per hour at idle.



I don't know what the driver's bank transaction was but let's assume that it was something she (I saw that it was a woman - no implications intended) could have done at the walk-up ATM. This matters since it is clearly worth more to avoid going inside the bank than to avoid the walk-up ATM.



I think the estimates I made for times at a window in my earlier post would be applicable here, so I'll say that she burned a net three minutes worth of fuel that could have been saved had she parked and walked up. That three minutes of pistons going up and down in cylinders used about .024 gallons of fuel which cost about $0.074. So her use of the drive through meant that it was worth at least about seven cents to avoid going to the trouble of parking and walking to the ATM.



I'll guess that she might use some sort of drive through window four times per week, so she might burn about five gallons of fuel per year while driving through, worth about $15.00. If she were to be presented with these numbers, do you suppose she'd immediately cease use of the drive through? I'm thinking that this is one of the few answers of which I can be sure. Actually, she'd have two answers: "no" and "HELL NO!!"



I wonder where her "point of indifference" would be? Surely she wouldn't use the drive through if it cost, say, $100.00 per use versus the walk-up ATM. What about $10.00? $1.00? I'm going to hypothesize that an average H2 driver would drive through for a dollar and walk up if the price differential were any higher. That would imply that a gas price of (100/7.4)*3.12=$42.16 per gallon would be the threshold of removing her from her car. There's a lot of room for gas prices to go up before certain lifestyle choices would change. I don't think drive through windows will be shuttered anytime soon.