Check out the latest or last issue of either Popular Science or Popular Mechanics. Can't remember which. They did a survey of about ten of them. All were POS. Most degraded fuel efficiency and some were downright dangerous.
ETA: No free lunch.
The latest issue of Popular Mechanics has an article on these. They are ALL a waste of money. In fact most of them decreased fuel mileage.
The only way to maximize fuel economy for your vehicle is the way you drive it.
From the way people drive around me, nobody gives a rat's butt about gas prices. Miffy in her 2500 Suburban going 80, darting in and out of lanes probably isn't footing the bill for her gas anyway.
Maintenance also has a significant effect.
Tire pressure is a biggie - Merely inflating the tires to the maximum recommended pressure can easily give you a 2-3 percent improvement in fuel economy.
As for engine mods, one that's worth considering is an engine oil cooler. Most oil grades are thicker than they have to be 99 percent of the time, simply to ensure sufficient viscosity during that one percent of the time when oil temperatures are at their highest. An oil cooler keeps the temperature low enough to safely run a lighter grade of oil, which reduces frictional losses.
Synthetic oil can also be used to advantage in the same manner - A thinner grade can often be substituted, because synthetics maintain their lubricating abilities at higher temperatures than conventional oils.
I saw that too.
I gained 4 MPG by inflating my tires and using cruise control.
'98 Corolla. Now I'm running @ 36MPG or so...
well... I've done a little looking into the gas situation. I've posted something like this before and got similar replies.
All I can think of is some Marvel Mistery oil and maybe a little PRI fuel treatment.
I've done a little math with the PRI products. 1 OZ treats 16 gallons of fuel and about 1.875 cc's treats a gallon to a gallon.
Consolidate trips - try and schedule your trips and combine them. Many times just making a decision to go to a different side of town to shop can lead you to major price savings at the pump.
Avoid "reving" the engine, especially just before you switch the engine off; this wastes fuel needlessly and washes oil down from the inside cylinder walls, owing to loss of oil pressure.
Eliminate jack-rabbit starts. Accelerate slowly when starting from dead stop. Don't push pedal down more than 1/4 of the total foot travel. This allows carburetor to function at peak efficiency.
Avoid prolonged warming up of engine, even on cold mornings - 30 to 45 seconds is plenty of time.
Don't start and stop engine needlessly. Idling your engine for one minute consumes the gas amount equivalent to when you start the engine. Avoid the drive through at the fast food restaurant.
Buy gasoline during coolest time of day - early morning or late evening is best. During these times gasoline is densest. Keep in mind - gas pumps measure volumes of gasoline, not densities of fuel concentration. You are charged according to "volume of measurement".
Normally the best time to buy gasoline from a pricing point is Wednesday morning. The prices are usually moved up for weekend by the oil companies and by Wednesday you have had three days of competition setting in among the stations to help drive the price down a few cents.
Most stations generally raise or lower their prices in the morning - around 10 AM. Expect a rise to occur on Thursday morning.
Some stations are fast to rise prices when they are going up, some are slow to go up. If you find that the price has gone up when you go to lunch, try and find one of those slow movers in your area so you can still purchase the cheaper gasoline.
Choose type and brand of gasoline carefully. Certain brands provide you with greater economy because of better quality. Use the brands which "seem" most beneficial.
Avoid filling gas tank to top. Overfilling results in sloshing over and out of tank. Try never to fill gas tank past the first "click" of fuel nozzle, if nozzle is automatic.
Slow down when possible - driving 55 mph can save up to 10% on gas mileage vs. driving 65 - 70 mph. This is due to wind resistance.
If your car has an overdrive gear, use it. Traveling at fast rates in low gears can consume up to 45% more fuel than is needed.
Manual shift driven cars allow you to change to highest gear as soon as possible, thereby letting you save gas if you "nurse it along". However, if you cause the engine to "bog down", premature wearing of engine parts occurs.
Keep windows closed when traveling at highway speeds. Open windows cause air drag, reducing your mileage by 10%.
Drive steadily. Slowing down or speeding up wastes fuel. Also avoid tailgating - the driver in front of you is unpredictable. Not only is it unsafe, but if affects your economy, if he slows down unexpectedly.
Think ahead when approaching hills. If you accelerate, do it before you reach the hill, not while you're on it.
Think ahead at stop signs and stop lights - no need to race up to a red light and then jam on the brakes to slow down. Plan to slow down before the light. If you can slow down soon enough to not have to stop at the light, you can save quite a bit a fuel versus starting from a standing start.
Stoplights are usually timed for your motoring advantage. By traveling steadily at the legal speed limit you boost your chances of having the "green light" all the way.
Regular tune-ups ensure best economy; check owner's manual for recommended maintenance intervals. Special attention should be given to maintaining clean air filters... diminished air flow increases gas waste.
Remove snow tires during good weather seasons; traveling on deep tire tread really robs fuel!
Inflate all tires to maximum limit. For each pound of pressure the tire is under inflated, you consume about 1% more fuel. Make sure you carry in your car an accurate tire gauge and know what the pressure should be. Check your tires at least twice a month and always before, during and after long trips.
Remove excess weight from trunk or inside of car - extra tires, back seats, unnecessary heavy parts. Extra weight reduces mileage, especially when driving up inclines.
During cold weather watch for icicles frozen to car frame. Up to 100 lbs. can be quickly accumulated! Accumulated snow and ice cause tremendous wind resistance. Try and keep your car clean at the carwash when possible..
Avoid using roof top carriers - they can cause serious drag on the car and lessen your mileage by up to 15%. Pack it in or leave in behind.
Buy a K&N high flow airfilter. More efficient = less fuel.
If your OEM air intake is overly restictive, you might find a small increase in mileage from an aftermarket intake to improve the sitation.
I did, and mileage improved by about 2mpg and also improved throttle response and power a slight bit.
Explain to me again why you think GM, Ford or Dodge wouldn't install these on their trucks and SUV's to increase Corporate CAFE numbers, give them another marketing plus to use against the others, etc etc etc? Oh that's right they liked to get kicked around by the lefties over mileage and lose sales.
Like the miracle carburetors that increase efficiency by 25%, GM really likes being in bed with the oil companies and therefore passes up what could be the thing that increases their sales almost infinitely?
Start squeezing them snakes boys.
You could always buy a bike
I have a '92 Honda Civic, and, I'm laughing at everyone now.
Oh? Gas 3 Bucks a gallon? I didn't notice
I'm not "Car guy"
I'd sooner burn my money and flush it down the toilet than spend it on gas.
That's just me.
I have a 2001 Saturn SL1, and I drive about halfway to work on backroads (paved) and the rest on a highway. I was getting 32 mpg the way I normally drove.
Last tank, I took my time. Drove 45-50 on the back road, and cruise control 55 on the highway. Never went above 55. My mileage last tank was 39.2 mpg! With a 35 mile each-way trip, that's a whole day of commuting, FREE!
I'm getting up an extra 5-10 minutes and doing it this way from now on.
Helping one's engine breathe better is a help too. Not that you might want to install headers on a minivan or anything, a better airbox & less restrictive muffler will add a few mpg's on about any vehicle.