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Summer 2010
Published quarterly
Volume 7, Number 3

Fuel Saving Gimmicks

Wacky fuel savings devices do not workEvery so often the old story surfaces about someone who invented a special carburetor. The story goes, the carburetor would allow any vehicle to get a hundred miles to the gallon. It continues, that the oil companies bought all rights to the device and quickly hid it away.

As nice as thoughts of such a device might be, they are simply not reality. Physics teaches that it takes a specified amount of energy [gasoline,] to move a given weight [vehicle,] a given speed, with a given engine design. To expect any single component on an engine to change this is wishful thinking at best.

In reality better fuel economy is a factor of a great many things. Engineers use more efficient engine designs, lighter vehicles, improved aerodynamics and decreased rolling resistance among many other things to improve mileage. It is in their best interest and several Government mandates specify that vehicles get the top mileage possible.

While fuel savings gimmicks may seem inviting, they are just that, gimmicks. I have never seen one that improves mileage above their cost and some can be harmful.

When desired fuel mileage is not being obtained with a present vehicle, many times a new vehicle is considered as the only remedy. There are really no changes that can be made to a vehicle to increase the mileage significantly over that it was designed to deliver. The present vehicle can often deliver considerably better mileage than it currently does, however.

The Engine Temperature Connection

An engine that is too cold waste fuelOften not considered, a major factor in fuel mileage is engine temperature. To an engine, 180 degrees Fahrenheit is considered very cold. Cold engines atomize fuel poorly and are very inefficient to operate. This is why old carbureted engines had chokes. This allowed more gasoline to be added, to have the cold engine run acceptably well.

A considerable amount of extra fuel is needed to make a cold engine run properly. With a fuel injected engine this is accomplished by increasing the pulse-width of the fuel injectors. The fuel injector operates much like a valve. It is held open longer, to allow more fuel to enter the combustion chamber. Perhaps as much as fifty-percent extra fuel may be added under certain conditions. This can burn a lot more fuel, so several efforts are made to speed warmup of the engine.

There are several mechanisms that help maintain the engine's temperature at acceptable levels. Among these are the engine thermostat and the cooling fans. The thermostat can close to block the flow of coolant in the engine. It remains closed until the engine reaches the proper temperature. At that point it will regulate the flow of coolant to keep the engine at the correct temperature.

In time coolant thermostats can fail or get weak. When this happens they can remain open or open prematurely. This can keep the engine from reaching full operating temperature and cause it to burn more fuel. Engine fans are also switched off to help the engine reach full temperature more quickly. A sticking relay, bad sensor or several other faults can cause fans to run when they should not.

Several additional functions are also related to engine temperature. For instance, the computer that maximizes fuel economy may not fully control the engine until a preset temperature is reached. This is because some of the sensors needed for input do not function until they are fully heated. When in this state, the computer often runs on preset or default-settings rather than those custom optimized for fuel economy.

Modern heated oxygen sensors help overcome this problem. These sensors contain heating elements that allow the sensors to control fuel much quicker. When the element fails, fuel mileage will suffer.

The transmission may also be effected. Some transmissions will not shift into overdrive until a preset temperature. This is to help the engine warm up faster. It can also burn a lot more fuel if the system is not working as designed. A weak or bad thermostat or even a faulty temperature sensor can effect this situation. There is also a condition known as "lockup" that helps with mileage. Several things can keep a transmission from going into lockup, including temperature and even a bad brake light switch.

The State of Tune

Certain components wear as an engine ages and this can reduce fuel mileage. Spark plug gaps wear reducing their efficiency. Plug wires and ignition coils can also fail and cause a decrease in performance as well as mileage. Some engines need spark plug replacement every 30,000 miles. Others can go much longer, because they use different types of spark plugs.

Recommended spark plug replacement is listed in the owner's manual. You could also have a trusted professional advise you, particularly if the vehicle has over 50,000 miles. Even spark plugs that are not completely worn out, can sometimes benefit fuel mileage by being replaced. See our section on Vehicle Maintenance for even more ideas on saving fuel.

Check engine lights too should never be ignored. They can indicate a fault that is causing fuel mileage to be decreased as well as many other concerns. Even if there are no symptoms at all, a problem that causes a check engine light can also cause other expensive damage.

Not Me? The Driver Connection

Driving habits may be the largest influence on fuel mileageIt is a fact that driving habit is one of the leading causes of excess fuel consumption. Several miles to the gallon can often be gained with little more than a change of driving style. Just as it requires more energy to run across a field than to walk across the same field, a vehicle requires more fuel to move faster. Driving 68 mph rather than 72 can save a considerable amount of fuel.

Accelerating is also a large consumer of fuel. The old, "drive like there is an egg under the accelerator," was never more true. Accelerating at a slower rate can greatly reduce fuel consumption. Coasting is also a good way to save fuel. Letting off of the throttle and coasting to a red light saves fuel as well as a good deal of wear and tear on brakes.

All modern vehicles have "adaptive learn function." This means they will learn and adapt to the way the vehicle is driven. Accelerate harder and the shift points will be raised in the transmission. When an engine computer receives request for power it adapts the engine to produce power, rather than economy. This adaptation can take considerable time to return to normal.

Other tips like keeping tires inflated, switching to an energy conserving engine oil and reducing unnecessary weight also help, but to a much smaller degree. Replacing a dirty air filter is always a good idea, but will NOT help fuel mileage.

Often with a change of driving style, and bringing the present vehicle up to peak performance, the same or better mileage can be had without the expense of a new vehicle. It is also important not to loose site of reason. Increased fuel mileage is great, but total cost is what really matters. An example might be, moving from a vehicle that gets 20 MPG to one that gets 30 MPG. With 12,000 miles per year and with fuel cost of $4.00 per gallon, the savings is $800.00 per year. Paying $25,000 plus for a new vehicle will require over 31 years to break even, not counting higher additional cost.


On the AGCO web site are several calculators you can use to more fully understand fuel/cost savings.