How to Stay Cool and Save Gas

With American drivers suddenly looking for every way to save on the cost of driving, I thought I would revisit an old question,

“Which is more efficient, air conditioning or open windows?”

I first ran into this question while in college at the University of Michigan. I had a roommate who had heard that the refrigerant used in air conditioning systems was bad for the environment so he went the whole hot and humid summer without turning on his car’s air conditioner. Of course, he didn’t realize that Freon (this was before it was replaced with R-134a as a refrigerant in cars) isn’t actually released into the atmosphere when you run your A/C. Air conditioning runs in a closed loop and the environmental concern about the chemicals comes when some is accidentally released during servicing or if the system develops leaks… ironically most likely to occur after long periods of disuse. Running the A/C system distributes lubricating oils to the seals in the system so an unused air conditioner could develop leaks.
Of course, when faced with this information he changed the topic to say that it was more efficient to drive with the windows open because air conditioning makes the engine work harder. Ah, perhaps he had a point? Frankly, I didn’t have an answer.

Years later, I was working on the GM EV1 (electric car) program. If you didn’t know, this was the most aerodynamic production vehicle ever offered for sale with a coefficient of drag of 0.19. Since the car carried so little energy on board (the 1,200 lbs of lead-acid batteries provided the energy capacity of about ½ gallon of gasoline… providing about 60 miles of driving range) every step was taken to minimize the use of that energy. Besides weight savings to conserve energy when accelerating, air drag is the biggest, well, drag when driving at speed. As an example, I was once told that they didn’t use a mast-style radio antenna because it would have cost nearly a mile of range.

Anyway, we often had to drive the cars around Los Angeles and Phoenix for various events and the question arose whether we were better off using the A/C or opening the windows for maximizing range. There was no hesitation from the engineers: They said that we should make ourselves comfortable and use the A/C with closed windows when driving over 55 mph. I wish I had this information at hand when I was sweating in my roommate’s car on a 90 degree Michigan day!

Why is this the case? Well, while running the A/C does put a drag on your efficiency, running with the windows down does as well. It isn’t that simple, though. The aerodynamic drag varies with your speed. Air drag increases exponentially as speed increases, so driving 75 mph requires much more energy than driving 55 (sorry, Sammy Hagar).

At freeway speeds, this drag becomes greater than the cost of running the air conditioning compressor.

While perusing the web, I came across a study by the Society of Automotive Engineers (PDF) that looked at this exact question. They found that at high temperatures the cost of running the A/C was between 5% and 10%. However, the drag caused by running with the windows down at 68 mph (110 Km/h) varied from 8% to 20%. The lower number was for SUVs… basically, cars with bad aerodynamics in the first place suffer less from the effects of opening the windows. The 20% number was for a regular sedan. Though they didn’t disclose what type they used, they do indicate that it was a large sedan with a V8 engine. A really aerodynamic car like a Honda Insight or a sleek coupe would be effected even more.

So the bottom line is that around town, you are better off with the windows open but once at speed you should close your windows even if it means turning on your air conditioner.
If you drive a Hummer or a Mercedes G-Wagon with the aerodynamics of a brick… well it doesn’t really matter. Just go buy Exxon stock.

Of course, driving while suffering from heat stroke isn’t good either, so here are some other hints about staying cooler if you must run your air conditioner around town:

• Try to park under cover or use a window shade. The cooler your car is when you get in the less you’ll need to run the A/C to cool it down.
• In the same vein, if your car is hotter inside than the outside air, open your windows before turning on your air conditioner.
• Max A/C (a.k.a. recirculated air) isn’t always the best way to cool down. Again, if the air inside of your car is hotter than the air outside, you’re just running super-heated air through your A/C system. Use the fresh air setting until the interior temperature is lower than the air outside.
  

Steve Haas

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I've got gas, and you can too! Getting Better Gas Mileage by a Mechanic

Question: I can’t afford a new car, and the price of gas is killing me. How can I get the most mileage out of the car I already own?

This question was asked of me recently as the price of gasoline is above four dollars and the price of diesel requires you to take a second mortgage out on your home before tanking up. Obviously, everyone doesn’t have the financial means to purchase a new vehicle, even though OPEC seems to think we do. Thus I will list the things you can do and have done to maximize your mpg.

First off, I would like to preface this with a no-nonsense disclaimer. You will not get 50mpg out of a carbureted big block V-8 without spending more on the conversion than you would on fuel anyway. Is it possible? Yes. Is it expensive? Very. Is it so expensive that it is probably out of reach for someone who can’t afford a new car? Yes. So…the following is a list of things you can do to improve your gas mileage without breaking the bank.

Keep your tires fully inflated to the tire sidewall pressure. (where it says XXpsi (cold) Tires that are low on air require more energy to turn because there is more rolling resistance between them and the ground. The more energy your engine has to use, the more fuel it will burn.

Lighten your vehicle. It is easier than you think. Go through your trunk and remove everything that you haven’t used within the last six months except the spare tire and jack. The less weight there is in your vehicle, the less power it takes to move it and the less fuel you will burn. If you have AAA coverage, you can take out the spare and the jack too but make sure to replace them before a long trip.

Use the air conditioning sparingly. The air conditioning system on a vehicle take a lot of energy away from the engine and burns a lot of fuel, so use it sparingly. If you are in city traffic, roll down your window instead. If you are on the highway turn the A/C on for a few minutes and then turn it off. Rolling down your window on late model cars while on the highway actually burns more fuel than running the air conditioning because of wind resistance.

Turn off your car. If you are waiting in a drive-thru or waiting for someone, turn off your car. There is an old saying that starting your car burns more fuel than just leaving it run. This is false. It also doesn’t cause that much more wear and tear on the engine so the greatest benefit is to turn the car off

Ease up on the throttle. Acceleration burns more gas than driving at a constant speed, so avoid fast starts and don't exceed the speed limit on the highway.

Drive conservatively. Leave a bit more distance between you and the person ahead of you in stop and go traffic. That way when the person in front of you stops you can take your foot off of the accelerator and coast for a bit. If you have left enough room then by the time you get to where you would have stopped anyway, the person in front of you has probably already sped up again. This has an added effect that it causes less wear to your braking system and actually helps clear up traffic because the person behind you will see that your brake lights not come on and will maintain a more consistent speed. Plus it is a safer way to drive because it give you more reaction distance should the person in front of you slam on their brakes.

Change your oil and air filter regularly but not your spark plugs. Huh? Don’t change my spark plugs? Your engine oil reduces friction in your engine, less friction means less energy used to keep the engine running so less fuel used. Your air filter, when it is dirty, can cause the engine to run a little rich causing you to lose power and burn more fuel. As for the spark plugs…New spark plugs have less resistance to make a spark than old ones as old ones have built up carbon on them from burnt fuel. That extra resistance causes a hotter spark to overcome the resistance of the carbon deposits on the electrodes, which causes the fuel/air mix to burn hotter and causes the ignition timing to advance very slightly. Which will produce a bit more power and a bit less fuel consumption. So only change your spark plugs if one or more is not working.

Get a tune up. Your local mechanic (or you) can perform a tune up on your car that will make the engine run more efficiently and useless fuel. The typical tune up consists of: New PCV valve, new EGR valve, oil and filter change, re-time the engine and adjust the valves.

Lube your drive train. Your local mechanic (or you) can perform a full drive train lube and service which consists of removing and replacing the differential and transmission oil and lubricating the suspension, driveshaft and steering linkages. This will reduce friction in the drive train, requiring less energy to make things move. It will also cause your bearings, bushings and seals to last longer.

Service your bearings. Your local mechanic can service your axle bearings which will remove a lot of friction from your drive train. It is not uncommon to get 30-70 more miles per tank of fuel with new or serviced bearings. Since this usually requires removing the wheels, hubs, jackshafts and brake assemblies I recommend having a professional mechanic do this service unless you know what you are doing. If your bearings are sealed cartridge bearings, have them replaced. If they are loose “cup and cone” or “cup and race” bearings, have them inspected, cleaned, lubed and re-installed or replaced if necessary. Ensure the mechanic uses a torque wrench to achieve proper bearing pre-load (a lot of them just tighten until the wheel doesn’t turn and then loosen ¼ turn, this is incorrect)


Finally, if you just need to go up to the store on the corner, or run a quick and close errand, consider walking, biking, roller-skating, jogging, walking on your hands, riding a scooter or skateboarding instead of using your car. Even the most efficient hybrid car in the world gets worse fuel mileage than you do.


Grimy Handshakes,
The Motachanic

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Fuel Saving Tips that Make Cents: Saving Money & Being Green

This is David Denberg, one of The Many Mouths of Mota. Today, I am posting as MotaGreen.

Monday, June 16, the national average per gallon of regular gas reached $4.08, the highest ever recorded in US history. Given rising demand trends and stagnant supply it doesn’t seem like oil prices are coming down, which means more money out of our pockets to live the same way we did a year ago. There are solutions that won’t necessarily solve America’s larger foreign oil dependency problems, but can save us as individuals some money.

Five things I did without spending more than five dollars increased my fuel efficiency from 15-30%, which translates into $0.60 to $1.20 per gallon of gas used. Not only can you save yourself money by embracing these simple steps, you’re reducing your carbon footprint. For those who don’t want to accept the general consensus of global warming, the financial savings should be enticing enough. For all you believers, what better way to say you’re doing your part than by reducing emissions of your vehicle and saving money which can be put towards other environmentally friendly improvements.

1. There is very little I love more than feeling the true power of my engine kick into action and propel me from 0-60 as fast as possible. Despite this joy, I recently changed my driving habits because this truly kills gas efficiency. I didn’t really mind when gas was $2/gallon, but those days are long gone. The realization was solidified when it cost me sixty-two dollars for a full tank that, three years ago, cost only twenty-eight dollars. Changing one’s driving habits is the single most influential factor when improving your MPG, and it’s completely free. It requires a shift in driving mentality, which isn’t always easy, but the rewards are worthwhile.
2. While in the gas station I decided to check my tire pressure and was shocked to see they had deflated considerably since my last check several months ago. Incorrect tire pressure by only 5 psi can reduce MPG by 10% and cause greater wear and tear on your tires, costing you more to drive than it should. Simple things that commonsense would suggest can increase your MPG by several gallons. Not driving with unnecessary weight in your car for example, for each 100lbs MPG goes down by 1-2 miles per gallon.
3. For highway driving, cruise control at a comfortable speed can increase efficiency an additional 1-2 miles per gallon.
4. Car companies consider aerodynamics when designing, so should you! If you have a rack on your car or some other object that obstructs wind flow you might want to consider how often you use it, and if it merits permanent placement.
5. Lastly, it is imperative that you use gas only when it’s needed! Sounds simple, but so many people leave their car running for too long, anytime you idle over 30 seconds it is using more energy than re-starting the car. In a long line at the fast food drive thru? Turn off your engine!
   

In total these steps took about 1 hour and can save you hundreds of dollars every year. There are other ways to astronomically reduce your fuel consumption, though it requires a much larger investment. For the time being, I’m happy with my increased efficiency, at virtually no cost.

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