Fact or fiction? 8 gas-saving myths

Let's examine some commonly held beliefs about how to get the best gas mileage from your vehicle.

By MSN Money Partner Apr 15, 2011 4:32PM

This guest post comes from Lou Carlozo, Green Dad columnist for dealnews.com.


The Kelley Blue Book folks have just named their top 10 green cars for the 2011 calendar year, a seeming boon for drivers seeking eco-friendly automotive alternatives. But if you're anything like me, you might think it's not easy being green, especially when the path to environmental friendliness runs straight through your wallet like a Hummer on steroids.


A bare-bones 2012 Ford Focus -- No. 10 on the Kelley list — runs $16,270. And that's cheap compared with the fourth-ranked Lexus CT 200h, weighing in at $29,120, also without options. Ugh. To add insult to injury, any new car depreciates the second you drive it off the lot. Post continues after video.

So for those of us who don't have five figures to spend on a gleaming set of wheels, take heart: The greenest car may well be the one you already have, provided you take steps to make it more fuel-efficient and environmentally sound. This is especially so because you're going to need those five figures to pay for skyrocketing gasoline this summer (you can also follow my tips on ways to save money on gas).

This week, Green Dad sorts the fiction and fact when it comes to making your machine run in harmony with the planet.


Fact: Driving slower saves you gas. Like millions of Americans, I listen to the "Car Talk" guys on National Public Radio mostly because they make me laugh. But they also dispense great auto advice, and they stress that slowing down makes a big difference: For every 1,000 miles you drive (figuring gas at $2.50 a gallon and 25 mpg fuel efficiency), you'll save as much as $15 driving 10 mph slower. Of course, if gas is nearly double that price,  the savings should double as well. Something to think about if you're a speed demon.


Fiction: Replacing the air filter on your car improves mileage. Every time I go for a quickie oil change, the tech comes out with an air filter that looks like dirt, which shames me into coughing up to replace it. But if your motivation is better gas mileage, consider skipping the change. The U.S. Department of Energy reports that an air filter change will mostly help your acceleration, not your mileage -- though if you drive an older car with a carbureted engine, it may improve fuel economy 2% to 6%.


Fact: Stepping on the brakes wastes gas. This one also comes courtesy of Click and Clack on "Car Talk." "Every time you use the brakes, you're wasting the 'acceleration' you've already used. Instead of moving your car, that energy is being transformed into steaming hot brake pads," they say. Instead, learn to anticipate stops, and gently accelerate your car from a standing stop. For more of those great "Car Talk" tips, click here.


Fiction: Gas-saving additives can improve fuel economy by 20% or more. What's the difference between motor oil and snake oil? Not much, if you're weighing the claims of slick entrepreneurs who know the timing's right for selling you magical gas-saving potions. To be sure, some long-standing products with modest claims (such as STP Gas Treatment) have vigorous supporters, but they only claim to boost mileage about 10%.


But as the Federal Trade Commission warns, "The Environmental Protection Agency has evaluated or tested more than 100 alleged gas-saving devices and has not found any product that significantly improves gas mileage. In fact, some 'gas-saving' products may damage a car's engine or cause substantial increases in exhaust emissions."


Fiction: New "low-resistance" tires significantly improve gas mileage. Unless you're driving bald or severely underinflated tires, the hype about low-rolling resistance tires adds up to minimal gas savings. As this story by USA Today reports, various brands of these newfangled tires create gas savings of only 1% to 3%, even if rolling resistance is cut by 25% or more. Whether that saves wear and tear on your car is another story, but the mileage improvements won't even pay for a spare tire over the course of 10 tanks of gas.

Fact: You can realize dramatic mileage improvement by replacing your oxygen sensor. This falls under the category of tuning up your car, always a good idea if you want to see gas mileage gains in the 4% range. As a function of any proper tuneup, ask your mechanic to look at the oxygen sensor; if it's not working properly, a simple repair to this part (commonly costing between $50 and $120) could boost your mileage by as much as 40%, the U.S. Department of Energy states.


Note that if you make this fix, it may take a few weeks for you to realize the improved mileage as your engine's fuel-air ratio adjusts.


Fiction: Topping off the gas tank is a good idea. I know, I know: You've finally found the one pump between here and Logansport, Ind., that has affordable gas, so why not squeeze every last drop into your tank? While that sounds sensible at first blush, here's the problem: Gas expands in warmer weather, which means topped off gas will likely wind up spilling out your tank.


As if you needed more incentive, check out this warning from the U.S. Environmental Protection Agency: "Topping off the gas tank can result in your paying for gasoline that is fed back into the station's tanks because your gas tank is full." So unless you’re in the mood to pay the folks at Exxon or BP a little more for your fuel, stop topping off your tank.

Fiction: High-octane gasoline improves your mileage. I'm amazed to see that countless drivers still fall for this marketing gimmick, despite abundant evidence that high-octane gas is a waste of money. Props to the folks at Bankrate.com for pointing this out, along with other gas-saving tips you can read here. Bottom line: Unless your car specifically requires premium, skip it and go for low-octane fuel.


More on dealnews.com and MSN Money:


Apr 15, 2011 8:23PM
Replace air filters. Keep a close eye on your engine's air filter. When the engine air filter clogs with dirt, dust and bugs, it causes your engine to work harder and your car becomes less fuel-efficient. Replacing a clogged air filter could improve your gas mileage by as much as 10 percent and save you 15 cents a gallon. It's a good idea to have your engine air filter checked at each oil change. The Car Care Council recommends changing your car's air and oil filters every three months or 3,000 miles or as specified in your owner's manual. This is bank rate and here is msn:

Fiction: Replacing the air filter on your car improves mileage. Every time I go for a quickie oil change, the tech comes out with an air filter that looks like dirt, which shames me into coughing up to replace it. But if your motivation is better gas mileage, consider skipping the change. Us dept. of energy reports that an air filter change will mostly help your acceleration, not your mileage -- though if you drive an older car with a , carburetor engine it may improve fuel economy 2% to 6%. What gives don't believe anyone
Apr 15, 2011 9:25PM
I will agree with all except the air filter and premium gas. The air filter will affect mileage and performance as lucky911 said. As for the gas, My 2003 Ram 1500 and my 1997 Ram 1500 both get 20 to 30% better mileage with 93  octane than with 85. The power is also considerably more. I was able to get 95 octane in Mo last summer. My wifes Montana van got 35% better than with 85 octane toilet water we have here in Co. We went to Columbia to pick up a load of furniture. We were getting around 275 to 300 miles per tank with trailer. We filled up with 95 in Collumbia and got 400 miles from that fill up coming back with the trailer loaded full. No one will ever convince me that gas doesn't make a difference except for some older cars like my 1972 Duster with slant 6 engine. It doesn't make much difference wheather I use premium gas or kerosene. It still gets about the same. I also had an Olds 98 with Rocket 455. It ran like #$%^ unless I used Premium Leaded. It would run great then.
Apr 15, 2011 9:25PM
Changing the air filter when it's dirty may not save gas, but it'll sure save an early engine overhaul!
Apr 15, 2011 10:16PM

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Apr 15, 2011 11:28PM
The author was right about topping your fuel tank, because it can cause your tank to explode. If there is no room for expansion, then it has to go somewhere.
 Another thing is to maintain the right size tire for your vehicle. You'll find that information inside the driver's door. The thing is, the bigger the tire, the faster you'll go. You might want to know that the next time you get a speed ticket, even if your speedometer says your are going the right speed. Always use the right size tire for performance and safety. This also saves the wear and tear on your vehicle.
Apr 16, 2011 12:32AM
Already knew Wal Mart was a dollar store. I hope I'm alive when the people screw the oil companies. And we will! Geothermal for your house, solar, wind. I just hope it's AMERICANS who make the the product. 
Apr 16, 2011 12:57AM

I'm another Car Talk Fan, listen to "Click & Clack" weekly.


But I have to disagree with your gas saving advise, or who ever advise it is. The trouble is I keep seeing the same erroneous advise.


A clean air filter is key to good mileage, carbureted or injected. Not to mention better for your engine. What you going to take the money you save by not cleaning/replacing your air filter, and replace your engine.


Tires are another thing. Keep them properly inflated! Better MPG, and saves your tires from wearing out prematurely. Tires ain't cheap, make them last.


Regular vehicle maintenance!  Take care of your car, and your car will take care of you. Not to mention last you many years. Unless you want to fork out 20-30 grand for a new one every few years.

Apr 16, 2011 2:08AM

The author is contradicted, the air filter only adds to acceleration and yet the brakes waste gas because you lose "acceleration". The air filter does save gas, I use the K&N air filter, with a 1,000,000 mile warranty it does pay for it's self. The KEY to good gas milage IS NOT any 1 thing, it is a number of things.


PROPER TIRE INFLATION: It will save a bunch on gas, the info for that can be found on the tire or on the sticker on the driver side door.


Do NOT TOP OFF FUEL: On newer autos it can saturate & damage valuable emissions componets.


READ OWNERS MANUAL: Some cars do take higher octane, follow the owners manual on schedueled maintenance and OIL. Most manual say in hotter temps use 5W 30 instead of 10w 30.


CHECK FLUIDS WEEKLY: Although it will not save on gas, it could save money on repairs and thats money you could put in the tank!


On manual transmissions: Higher gears will save money, the higher the engine revs the more gas it uses. use cruise control in automatics


Learn auto mechanics: Doing maintenance yourself will not save gas, but save you money you could put in the tank (there are some educational youtube vids on automechanics).


Visually inspect VACUUM LINES: vacuum lines run alot of emissions componets even a pin hole can cost fuel economy. Look for vacuum lines that are corroded and REPLACE.


There are alot more gas saving tips try checking your local DMV there could be a little pamphlet on fuel saving tips.


Apr 16, 2011 2:28AM

Some of those are true, and some aren't. I had an 06 cobalt and got better mileage with medium than regular. It wasn't significant, the extra mileage almost exactly offset the added cost, but regardless the mileage did improve.


My 04 RX8 went from 240 miles on a tank to up to 270 just by switching what company I get gas from.


Octane doesn't make a massive difference and depends on the car but regardless your car will run better with a higher octane so why not treat your car better?

Apr 16, 2011 7:06AM

Let me add my 2 cents here.  I tried the 0% ethanol gas in my SUV and I had gotten better gas mileage and my vehicle performed so much better.


I did the mileage on it after using it for a bit and I had gotten 363 miles out of a full tank of gas before my light came on, usually I only get 326.  It did cost me $68 to fill it up at 3.82 or 3.62 a gallon but it lasted me alot longer than if I had used the cheap stuff.  I also put in $10 of the 89 octane yesterday but it didn't last long at all, it was like I was using the cheap stuff.   I had gotten just a hair under a quarter of a tank of gas and my car did not run as well. 

Right now that gas cost $3.99 a gallon and I will be happy to hand over the money.

I feel like I am getting my money's worth using the 0% ethanol gas.  there was only one gas station here that I knew of that sold it.  Now there are two.  Hopefully it will be making a comeback.  If any of you see that sold in your area I would say go for it and don't even think about the extra money that you are paying at the pump.  It is well worth it.


This lady is happy going along with the 0%, my car seems to love it too.  I am all for helping out the eco system but I don't think it is worth it having the ethanol in the vehicle.  Now if my car was made for only that then sure I would use it but since it is not and not even a flex vehicle I am not worried about it.  My dream car is an all electric car to scoot around town in. Someday, someday. 

Apr 16, 2011 8:10AM
Here is a "Fact or Fiction" myth  I would have liked to have seen in this article. Its a common belief that if a truck owner lowers his tailgate,,it will save on gas because it reduces wind resistance. I have yet to see anything to confirm or debunk this. But as a truck owner myself,I tried this and haven't seen any difference either way. Does anyone have any thoughts on this?
Apr 16, 2011 9:11AM

Hi BillWP!  You wrote:  "Its a common belief that if a truck owner lowers his tailgate,,it will save on gas because it reduces wind resistance. I have yet to see anything to confirm or debunk this"


Actually, "Mythbusters" did. It's a myth.  There is a wave of air that passes rolls over an empty bed and it reduces drag with the tailgate closed compared with the tailgate open.  Detroit designers have done this type of study for decades to incorporate a drag component to trucks.

  The effect is similar to how the Kammback design works. 


  If you fill the bed, though a lot of things change for the flow...including putting on a camper.  A tonneau cover works well too and doesn't hurt drag from what I've seen.

  Keeping the gate closed is common knowledge up here in the Toledo-Detroit area because of the worker's commitment and proximity to auto technology. It's funny, union workers save billions in losses by  companies sometimes fixing bad designs and repairing weird management ideas and production methods with suggestions and study groups. Auto factory workers are some of the most interesting professionals in the world.  If you think this is a plug, it is. They put up with stuff and make stuff in ways you wouldn't believe.  They make it look so easy, by being pros, that you'd THINK it was easy!    I hope this helps!


Apr 16, 2011 10:45AM
Fact: Driving slower saves you gas.
They don't say exactly what slower is, but I track the fuel mileage on all my vehicles. I have seen the best fuel mileage vary from below 50 mph to 76 mph depending on the vehicle.
Not all vehicles are created equal.
Apr 16, 2011 11:17AM

Forget traveling 10 mph slower to save a few bucks.   I calculate that I would save between $15 and $20 dollars a month but adds 20 minutes more driving time a day in my car. 


No thanks.  My time is worth more than that. 

Apr 16, 2011 12:08PM
just did a comparison test in my 94 yj, got 13.9 mpg with a tank of 87octane with ethanol,then ran it empty, filled with nonethanol 87 octane and got  16.3 mpg, even at 20 cents more a gallon would realize a 41 dollar savings on a thousand mile trip, not to mention i also own a 99 tahoe and in the last 6 months had to replace muffler,then both catalytic converters, then the motor, and 3 oxygen sensors,all of which i attribute to my wifes short commute combined with ethanol gas,dont believe for a minute that this ethanol 10 -15 percent gas makes any sense, government snake oil for sure, going to cost us all in the long run.
Apr 16, 2011 12:14PM

All the oil companys are doing is getting there money back for the gulf oil disaster.  And for years we have been scammed for diesal as diesal is a by product after making gasoline.  They jacked up the price to catch all the diesal trucks, cars, rv's.  And put a tremendous burden on the trucking industry.

Apr 16, 2011 12:21PM
Don't believe Consumer Reports:Give the Fuel Doctor a try;especially if you have an OLDER car.My 1998 Cavalier is delusional;it thinks it's a hybrid after a months of the Fuel Doctor.
Apr 16, 2011 12:41PM
Come on people!  FORGET about the  ""clean" air filter, the oxygen sensor, or the OZONE layer..!  One guy hit it.  Its ALL in the way you PRESS on the gas and brake pedals...LOOK ahead at Green/Red lights and slow down to time your arrival to the light when it is green.  LIghten up on your braking/acceleration. Racing off the line at the green light is for the Indianapolis 500...not at the corner of Indian Way and Main Street, Anytown, America!!!  I dont need to "measure" my mileage at all.  Driving according to this method, of NOT RACING from one Red light to the next, gives me the Best mileage possible, saves on Brake wear and keeps my Blood Pressure @ 100/60!
Apr 16, 2011 1:11PM

No mileage effect, but this is the worst idea for saving money -- DON'T FILL YOUR TANK ON APRIL 15TH!  Instead fill up on the 14th or wait until the 16th.  That will cost the oil companies $3 billion and force them to lower prices by 30 cents per gallon!


So instead we give them an additional $1.5 billion a day early plus another extra $1.5 billion a day later!  Duh?  Who thought this one up?

Apr 16, 2011 1:31PM
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