First, a word about fluid disposal…

Used fluids such as engine oil, transmission fluid, ethylene-glycol antifreeze and brake fluid are hazardous wastes and must be disposed of properly. Before draining any fluids, consult with your local authorities; in many areas waste oil, etc. is being accepted as a part of recycling programs. A number of service stations and auto parts stores are also accepting waste fluids for recycling.

Be sure of the recycling center's policies before draining any fluids, as many will not accept different fluids that have been mixed together.

Gasoline is a hydrocarbon (composed of hydrogen and carbon), produced by refining crude oil or petroleum. When gasoline burns, these compounds separate into hydrogen and carbon atoms and unite with oxygen atoms. The results obtained from burning gasoline are dependent on its most important characteristics: octane rating, volatility, lead content, and density.

Octane rating
See Figure 1

Simply put, the octane rating of a gasoline is its ability to resist knock, a sharp metallic noise resulting from detonation or uncontrolled combustion in the cylinder. Knock can occur for a variety of reasons, one of which is the incorrect octane rating for the engine in your car. To understand why knock occurs, you must understand why knock doesn't occur. So let's look at the normal combustion process.

Under normal operating conditions, the firing of the spark plug initiates the burning of the fuel air mixture in the combustion chamber. Once the plug fires, a wall of flame starts outward from the plug in all directions at once. This flame front moves evenly and rapidly throughout the entire combustion chamber until the entire fuel/air mixture is burned. This even, rapid progress of the burning fuel/air mixture is highly dependent on the octane rating of the gasoline.

If the octane rating is too low, the last part of the compressed fuel/air mixture may ignite before the flame front reaches it, in effect creating two areas of combustion within the cylinder. However, while the original combustion is proceeding at a carefully controlled rate, this new combustion is simply a sudden sharp explosion. This abrupt increase in pressure is what creates the knocking sound in the combustion chamber.

As far as the piston is concerned, the damage inflicted by the increase in pressure (caused by the sudden explosion) is exactly like striking the piston top with a heavy hammer. Knock is very damaging to the engine, since it causes extraordinary wear to bearings, piston crowns, and other vital engine parts. Engines can actually be destroyed through excessive engine knock.

Engine knock can be controlled by using a gas with the proper octane rating. Octane measurements made under laboratory conditions have led to "Research" and "Motor" octane ratings. In general, the research octane number tends to be about 6-10 points higher than the motor octane rating (for what is essentially the same gasoline). Since the early seventies, most octane ratings on gas pumps have been the average of the research and motor octane numbers. For instance, if the gasoline formerly had a research octane rating of 100, and a motor octane rating of 90, the octane rating found on the pump now would be 95.

Your owner's manual will probably indicate the type of gasoline and octane recommended for use in your car. However, octane requirements can vary according to the car and the conditions under which it is operating. If you encounter sustained engine knock, wait until your tank is nearly empty, and then try a gasoline with a higher octane rating. Don't needlessly overbuy - it's a waste of money to buy gasoline of a higher octane than your engine requires in order to satisfy its anti-knock need.

As a new car is driven, combustion deposits build up and the octane requirement increases until an equilibrium level, normally between four and six octane numbers higher than the new-car requirement, is reached. Other factors which can increase the octane an engine requires are higher air or engine temperatures, lower altitudes, lower humidity, a more advanced ignition spark timing, a leaner fuel/air mixture, sudden acceleration, and frequent stop-and-go driving which increases the build-up of combustion chamber deposits.

Catalytic converters and unleaded fuel

Since 1975, most cars have been equipped with catalytic converters, making the use of unleaded fuel mandatory. All cars equipped with catalytic converters have a restricted filler neck opening that will only permit the use of the smaller nozzle used on unleaded gas pumps. The use of leaded gas will not harm the engine, but will destroy the effectiveness of the converter and void your warranty.

Lead content

Older, higher-compression engines usually required a gasoline with a higher octane rating. The most efficient way of increasing the octane rating of a gasoline was to add a compound called tetraethyl lead. Should circumstances force you to use a low-lead or no-lead gasoline with lower octane than the car manufacturer specifies in an older lead fuel car, you should temporarily retard the ignition timing very slightly in order to lessen the possibility of knocking. Some cars, though designed to operate on leaded gasoline, may be able to use low-lead and no-lead fuels. Again, experimentation is helpful in determining the gasoline octane that your car and your driving require.

Volatility

The volatility of any liquid is its ability to vaporize, and gasoline must vaporize in order to burn. A highly volatile gasoline will help a cold engine start easily and run smoothly while it is warming up. However, the use of a highly volatile gasoline in warm weather tends to cause vapor lock on carbureted engines, Vapor lock is a condition in which the gasoline actually vaporizes before it arrives at the carburetor jet where vaporization is supposed to take place. This premature vaporization may occur in the fuel line, fuel pump, or in a section of the carburetor. When use of highly volatile fuel leads to vapor lock, the engine becomes starved for fuel and will either lose power or stall. Although refiners vary the percentage of volatile fuel in their gasoline according to season and locality, vapor lock is more likely to occur in the early spring, when some stations may not have received supplies of less volatile gasoline.

Density

Density is another property of gasoline, which can affect your fuel economy. It indicates how much chemical energy the gasoline contains. Density is generally measured in BTU's per gallon (the BTU, or British Thermal Unit, is a standard unit of energy), and usually varies less than 2% among most gasoline but can vary as much as 4-8%. This indicates that gas mileage could vary by as much as 4-8%, depending on the density of the gasoline you happen to choose.

Additives

The Environmental Protection Agency (EPA), through the Clean Air Act, has required that detergent additives, also referred to as Deposit Control Additives (DCAs) be added to all gasoline from January 1, 1995.

Practically as important as octane rating and volatility are the additives that refiners put into their gasoline. Carburetor/Fuel injection detergent additives help clean the tiny passages in the carburetor or fuel injectors, ensuring consistent fuel/air mixtures necessary for smooth running and good gas mileage. Other additives are used to help control combustion chamber deposits, gum formation, rust, and wear. One additive you may have noticed in your car is manganese. Since the advent of the catalytic converter and the resultant widespread use of unleaded gas, manganese has been used in many fuels as an anti-knock additive in unleaded gasoline. Manganese works, but it leaves reddish deposits on spark plugs. So, if you pull your spark plugs and notice that they are covered with what looks like rust, don't panic. It's only manganese and it's as harmless as the lead deposits it replaces.

Gasoline blends

The disruption of oil supplies from the Middle East in the 70's spurred an effort to try to curb the U.S. dependence on foreign petroleum sources. Interest in alternative fuels was also created by the reduction or elimination of lead anti-knock additives in gasoline. The lead was removed because of its incompatibility with the catalytic converter, now standard on almost every car and light truck.

Ethanol

Ethanol has attracted the most attention as a blend. It can be fermented from a variety of bases, including grain and sugar cane, much the same way wine is produced from grapes. The U.S. Environmental Protection Agency (EPA) allows a 10% ethanol mixture with gasoline and it is being sold as "super unleaded" or "premium unleaded" gasoline, gasohol, or with no specific identification.

Methanol

Methanol comes from natural gas, but the technology can produce it from coal, wood and a variety of other materials. Like ethanol, methanol raises the octane of gasoline and reduces engine "knock" or "ping", without affecting the efficiency of the catalytic converter. A 5% blend of methanol may raise the octane rating at the pump by 1-1.5 numbers.

• Methanol has an adverse effect on fuel economy, especially in late model cars. A 5% blend of methanol with gasoline has an energy content 2.5% less than gasoline.
• Evaporative emissions rise substantially when methanol is blended with gasoline. In addition, methanol may increase the oxides of nitrogen emissions and affect the capacity of the charcoal in the evaporative emissions canister.
• Methanol causes both hot and cold weather drivability problems. Methanol can change the stoichiometric (chemically correct) air/fuel ratio in the fuel delivery system. The higher volatility of the fuel increases the chance of vapor lock in carbureted cars and the increased heat of vaporization of methanol increases cold start and stalling problems in winter.
• Methanol, when water is present even in trace (minute) amounts will separate gasoline into 2 layers-gasoline rich on top and alcohol and water on the bottom. The net effect is unsatisfactory car operation. Since the engine draws fuel from the bottom of the tank, it will not run properly, even at idle. Some refiners add heavier alcohol, known as "cosolvents", to counter the separation, but they are not 100% effective.
• Methanol has an effect on the parts of the fuel system and is measured more in time than in mileage. Rubber, plastic and metal fuel system components in most motor cars were designed for use with gasoline and are subject to attack by methanol blended fuels. Water tends to cling to methanol, and any water in the fuel tank will be carried through the entire fuel system. Metal components (excluding brass) are subject to water corrosion. Plastic and rubber compounds tend to swell, lose strength and stretch when subjected to high concentrations of methanol.

Several fuel suppliers are successfully marketing blends of methanol and cosolvents with gasoline, but the long-term effects on engines and fuel systems are not known and car manufacturers will not give unqualified sanction to the use of methanol blended fuels.

Check your owner's manual to be sure.

Reformulated Gasoline

The Environmental Protection Agency (EPA), through the Clean Air Act, has mandated the use of reformulated gasoline in certain areas of the country from January 1, 1995.

Reformulated (RFP), is gasoline that the composition has been changed to reduce car emissions. Reformulated gasoline has lower levels of volatile compounds and benzene. RFP also contains an oxygenate such as ether or ethanol.

Any oxygenated fuel will reduce fuel economy, this is true simply because it has less combustible material per gallon. But, because of the reduction of volatile compounds, cars which are in poor mechanical condition may also experience an increased hesitation after start-up.

Reformulated gasoline differs from oxygenated fuel in that it is intended for year round use with reduced emissions, whereas oxygenated fuels are designed to reduce carbon monoxide levels during the winter season.

Because of their unique compression-ignition principle, diesel engines run on fuel oil instead of gasoline. The fuel is injected into the cylinder at the end of the compression stroke and the heat of compression ignites the mixture. Diesel fuel used in automotive applications comes in two grades, No. 1 diesel fuel and No. 2 diesel fuel. No. 1 diesel is the more volatile of the two and is designed for engines that will operate under varying load and speed conditions. No. 2 diesel is designed for a relatively uniform speed and high loads.

Cetane number

The cetane number of a diesel fuel refers to the ease with which a diesel fuel ignites. Don't confuse cetane ratings with octane ratings. Octane ratings refer to the slowing or controlling of the burning of gasoline. Cetane ratings refer only to the ease or speed of the ignition of diesel fuel. High cetane numbers mean that the fuel will ignite with relative ease or that it ignites well at low temperatures.

Viscosity

Viscosity is the ability of a liquid to flow. Water, for instance, has a low viscosity since it flows so easily. The viscosity of diesel fuel is important since it must be low enough that it flows easily through the injection system, while at the same time being high enough to lubricate the moving parts in the injection system. No. 2 diesel fuel has a higher viscosity than No. 1, which means it lubricates better, but does not flow as well. Because of this and its lower cetane rating, No. 2 diesel is not as satisfactory as No. 1 in extremely cold weather.

One more word on diesel fuels. No matter what you've heard elsewhere, don't thin diesel fuel with gasoline in cold weather. The lighter gasoline, which is more explosive, will cause rough running at the very least, and may cause extensive engine damage if enough is used.

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