We posted these before, but are some new things that make them not true.


6 gas-saving myths
Sure you want to save gas, but there's a lot of bad advice on how to do it. Some of it makes no difference, and some of it can wind up costing you.


By Peter Valdes-Dapena, CNNMoney.com staff writer
Last Updated: May 13, 2008: 3:11 PM EDT
NEW YORK (CNNMoney.com) -- With gasoline prices hitting record levels, it seems everyone has a tip on how to save fuel. Much of the advice is well-intentioned, but in the end, much of it won't lower your gas bill.

Here's a look at a few misconceptions:

#1. Fill your tank in the morning
You may have heard that it's best to fill your gas tank in the early morning while the fuel is cold. The theory goes that fluids are more dense at lower temperatures, so a gallon of cold gas actually has more gas molecules than a gallon of warmer gas.

But the temperature of the gasoline as it comes out of the nozzle varies little during the course of the day, according to Consumer Reports, so there's little, if any, benefit, to getting up early to pump gas.

#2. Change your air filter
Maintaining your car is important, but a clean air filter isn't going to save you any gas. Modern engines have computer sensors that automatically adjust the fuel-air mixture as an increasingly clogged air filter chokes off the engine's air supply.

While engine power will decrease slightly as the air filter becomes clogged, a lack of performance or an increase in fuel consumption will be negligible, Consumer Reports says.

#3. Use premium fuel
With prices already over $4.00 a gallon, premium gasoline is a hard sell these days. But a lot of drivers think because their owners' manual recommends premium, they'll get better fuel economy if they stick with it. Really, they're paying more money for nothing.

Even cars for which premium is recommended won't suffer with regular fuel. Modern engine technology comes to the rescue again. When sensors detect regular instead of premium fuel, the system automatically adjusts spark plug timing. The result is a slight reduction in peak horsepower - really, you'll never notice - but no reduction in fuel economy.

#4. Pump up your tires
Proper tire inflation is important for a number of reasons. Under-inflated tires are bad for handling and can even cause a crash. Improper tire inflation also causes tires to wear out faster and to heat up more, which could trigger a dangerous high-speed blow-out.

According to on-the-road driving tests by both Consumer Reports and auto information site Edmunds.com, underinflated tires reduce fuel economy, so proper inflation is key.

But you should never over-inflate your tires. They'll get you slightly better fuel economy because there will be less tread touching the road, reducing friction. But that means less grip for braking and turning. The added risk of a crash isn't worth the extra mile a gallon you might gain.

#5. To A/C or not A/C
There's no question air-conditioning makes extra work for the engine, increasing fuel use. But car air conditioners are much more efficient today than they used to be. In around-town driving, using the A/C will drop fuel economy by about a mile a gallon.

Meanwhile, driving at higher speeds with the windows down greatly increases aerodynamic drag. As speed increases, drag becomes more of an issue, making A/C use the more efficient choice at high speeds.

At most speeds and in most vehicles, A/C use drains slightly more fuel than driving with the windows down, contends David Champion, head of auto testing for Consumer Reports. "My final take on is that it's very close," says Phil Reed, consumer advice editor for Edmunds.com. "It's hard to measure the difference and every vehicle is different."

The best choice - if temperature and humidity allow - is to keep the windows

 

The only thing I have ever seen that seems to work pretty consistently is using a cotton gause, performance air filter. Before I added one the best I ever got was 25mpg once with an even driving mixture, when I dropped in my K&N I immediately got 27 mpg and was able to hit a peak of 29. I think one thing that can make a difference is where you get your gas from. The best results I have received have been from Texaco (which unfortunately is no longer available in this area), Gateway F/S, and Mobil. I have had lousy results with Casey's, Murphy USA, and Citgo (which I never go to unless an emergency). Have any of you found a difference.

 

In San Antonio, Shell seems to be the best. Valero (which is virtually everywhere, since the HQ is here), varies from tankful to tankful -- sometimes it knocks, sometimes it doesn't. I also use Exxon from time to time. It's about halfway between Shell and Valero.

Actually, the best gas mileage I've ever had has been on the Kansas Turnpike. I was able to get 32 MPG out of my '94 Thunderbird there (it usually got 28-30 on the highway) and 29 out of my '00 Mustang (usually 25-27). The surface of that road is incredibly smooth -- as it should be, since it's fairly costly to drive it. If anything, I'd say road surface is the single biggest difference (excluding wind, of course) there is when it comes to mileage.

 

We have Shell, BP, Phillips 66, Conoco, QT, Mobil, and Murphy USA (if you consider that to be a major name brand since it is found only at Wal-Mart) as our major name brands in this area. I haven't had as good luck with Shell, though I know lots of people who swear by it. BP is okay. Phillips is one of my back up places to go due to good results. I haven't had much experience with QT. I've never heard of Valero before so I'm guessing that is a Texas area thing. A few local chains we have in this area is Casey's (gas is lower grade but some items in the store such as donuts and pizzas are actually pretty good), Huck's (it's like Casey's without as good products and I never go there), Handee-Mart (this chain is becoming rare and for good reason, lower quality fuel), Gateway F/S (a farm co-op, farmers and truckers often go here, has E10 and/or E85 available consistently, many mechanics I know recommend it), MFA Oil (on the Missouri side another farm co-op from what I understand, just a Missouri version from what I understand, it was listed on the top tier fuel list so that says something), Moto Mart (middle quality fuel, has large quantities of items in their store), ZX (a lot of Citgos changed to this and I have never been there and have no plans on going there either), and a few other independents.

The absolute best I have ever received with my car is 36 mpg a few times with pure highway driving. 32 is my average on the highway.

 

I agree with Shell regular oil (Revell????) and gasoline being the best.

They have a major engine facility in Houston where they test gasoline and oil in engines and it like a huge ware house where all they is run engine for thousands of hours doing data acquisition.

 

I'm sure that Shell is one of the best considering they landed on the top tier fuel list, I just have had better luck with other ones is all.

The other thing I disagree with that list on is the no need for using premium point. Although it might not help the fuel economy, you should go with what is recommended because then the engine does not run at it's potential and sometimes despite what they would like to believe the electronics (like the water tight compartments on the Titanic) are not perfect and sometime will fail and the engine will detonate. Plus, premium can also be useful in the case of some gas stations like Shell that add extra additives and detergents that help to keep your engine clean.

 

I saw an episode of Mythbusters on the Ac/Windows down comparison (they used a ford expedition) and the conclusion was that driving with the windows down at all speeds saves fuel over using the AC by a significant margin, if I remember correctly they got 2 3/4 extra laps on the test track they used with the windows down.

 

So the so called "gas saving myths" are actually contain some myths. It's funny how these things work sometimes where people who claim something is a myth are actually the ones telling the myth.

 

You are partially correct. Consumer Reports' auto-test department reports that the air conditioner reduces your car's fuel efficiency by up to 10 percent. So to achieve maximum fuel efficiency, drivers should avoid using the air conditioner at speeds below 40 mph and travel with their windows down. Howver, Mythbusters found that as your speed increases to 45 mph, or highway speeds, wind drag becomes an issue. Driving with the windows down increases the drag on your vehicle, resulting in decreased fuel economy by up to 10 percent. Drive at speeds over 55 mph with windows down and you'll decrease fuel economy by up to 20 percent or greater.