Gas Saving Tips That Don't Work

[Eric]

Are you following bad advice when it comes to saving gas? Here are some tips you may have heard about that don't work as advertised:*

* Using premium fuel instead of regular -*

"Premium" fuel is a misleading term. The gas isn't better, it's just higher octane. If your car's engine doesn't need high-octane gas (your owner's manual will tell you) then you're just wasting your money by feeding it high-octane fuel. And that's not all. If you feed an engine designed to burn regular unleaded high-octane premium fuel, your gas mileage will probably decrease because your engine is not designed to burn the high-octane fuel, which reduces its combustion efficiency.*

* Not using the air conditioning -*

It's true that air conditioning draws power from the engine and that's why many people reason that not running the AC will save gas by decreasing the load on the engine. However, unless you also keep the windows rolled up, any efficiency gains achieved by not running the AC will be offset by the increased aerodynamic drag created by leaving the windows open for ventilation. Cars built before the 1980s - when AC was still a fairly rare option - often had ductwork that provided adequate forced air ventilation to the interior even with the windows closed. But modern cars don't have that feature, because most modern cars come standard with AC - and it's assumed you will use it, rather than leave the windows down.*

* Taking off your tailgate (pick-up truck owners) -*

There is some truth to this one, but not in the way most people probably think. It's not the improved airflow over the bed that kicks up the MPGs - it's the weight reduction that comes from taking off a fairly heavy piece of metal. If you can operate your truck without the tailgate, you might see a slight increase in your MPGs by taking off the tailgate. But don't go out and buy one of those expensive tailgate nets to replace it - unless you just like the looks or need something to hold your cargo in place - because the cost of the net will cancel out the slight potential mileage improvement you'll get by taking off the metal tailgate. *

* Filling up your tires to the maximum recommended air pressure -*

This is another Catch 22 "fuel saver." It's true that by filling up your vehicle's tires to the maximum allowable air pressure (listed on the sidewall of the tire) you may decrease your* vehicle's rolling resistance, which could, in turn, result in a 1-2 MPG uptick in your fuel economy. However, if you exceed the maximum recommended air pressure (see your vehicle owner's manual) it is also likely that your tires will wear out faster - and given the average $100-150 dollar per tire replacement cost - it is highly unlikely you'll come out ahead, money-wise. Also, if you inflate your vehicle's tires to a higher-than-recommended PSI, it will likely alter both ride quality and handling, as well as increase braking distances.*

* Turning off your engine at traffic lights -*

Hybrids do this, so why shouldn't you? Because hybrids have high-torque starters designed to quickly (and repeatedly) start the gas engine side of the hybrid gas-electric powertrain - and your standard (non-hybrid) car does not. It takes more energy to operate a conventional starter - and will wear that expensive part out sooner - if you overuse it by turning off your car's engine at every stoplight. You will also put unnecessary load on your battery, which may reduce its life.*There are, however, some situations where it does make sense to shut off your car's engine in order to save gas that would otherwise by used up just idling. If you find yourself caught in a traffic jam or work zone where it's clear you will be stationary for more than about 5 minutes, shutting down your engine is ok.*

[dom]

* Taking off your tailgate (pick-up truck owners) -*

I think just opening your tailgate does well enough. I've noticed a big different on my el camino with the gate down, but I also get pulled over for not displaying my plate.

* Turning off your engine at traffic lights -*

This is just dumb. Asking for repair bills!

[grouch]

Buying "fuel economy" devices are also things that don't work. A fuel economy gauge is really a vacuum gauge and if you watch it and feather foot your driving, it will do some good. However, most of the stuff out there does nothing and may even cause damage to the engine.

The Tornado is something that has been around since the early 20's in one form or another. It does nothing for a fuel injected engine. If it did something, you can bet the car companies would use a version of it. Race teams have machinists who do little but try to smooth out the air flow inside an engine. They are paid mega bucks to do this and the results are constantly tested on the track. The Tornado introduces turbulence which slows air flow instead of smoothing it out. It may have done something on a carbureted engine to atomize the fuel at the carburetor better but I haven't seen a carbureted car built in 20 years or so.

Magnets on the fuel line cost money but do nothing. Gasoline is not ferrous. They actually will grab rust particles and I use large ones on metal tanks to catch rust particles and keep from plugging up fuel filters. Most tanks today are plastic and don't rust. In an extreme case, I can see rust building around the magnet and either plugging up the fuel flow or collecting and then the pressure of fuel flow causing it all to hit the filter or injectors in one clump. Bad mojo there.

[swamprat]

Regarding the AC:

A coworker and I devised a comprehensive fuel economy test where he set the cruise on his 2005 Kia Sportage at 55, 60, 65, 70 and 75 mph on his commute to and from work. He also operated the AC and then turned it off. At all speeds, the car got 3-4 mpg less with the AC on than with it off and rolling down the windows. The car got better gas mileage at 70 mph with the AC off than at 55 mph with the AC on. AC is a killer of gas mileage.