Lubrication System
The engine is the heart of your vehicle. Hundreds of moving parts within the engine must be lubricated. While the engine burns gasoline, it also takes in air from the outside. Thousands of gallons of air are brought into the engine for every gallon of gasoline consumed. Road dust and dirt are brought in with this air. While most of the air is cleaned, some dirt and dust may get by the air filter. In addition, incomplete combustion adds carbon deposits to the oil. Water can also come in contact with the oil from humidity in the air and from gaskets leaking. All of these factors can lead to engine oil failure. Engine oil is the substance that keeps your engine going day after day. It is extremely important to keep the oil clean and at the correct level to prevent engine oil failure.

Purpose of Oil in the Lubricating System
Without oil an engine would not run. Engine oil is processed from crude oil and is specially formulated to do four main tasks within the engine:

• Lubricate
  
• Cool
  
• Clean
  
• Seal
  

Engine Oil Lubricates
The most important function that engine oil does is to lubricate. Within the engine there are hundreds of little parts rubbing up against each other. This rubbing creates friction. Friction is the force that resists motion between two bodies in contact. Engine oil molecules are like little ball bearings. The oil molecules have a tendency to stick to metal surfaces, but have less of a tendency to stick to each other. Oil decreases resistance and friction between two sliding bodies, resulting in a reduction of engine wear.

Engine Oil Cools
While engine oil does reduce friction, it obviously cannot eliminate it. Without engine oil, friction would build up undesirable heat, causing the engine to overheat, damaging internal components. Engine oil is pumped throughout the engine, moving into various parts and then back to the oil pan. In the oil pan or through an engine oil cooler, heat is dissipated to the outside air. Engine oil helps cool your engine in this process.

Engine Oil Cleans
The internal combustion engine is not very efficient (only about 28 cents of every dollar spent on fuel results in moving the vehicle). This inefficiency causes unburned deposits to build up within the engine. Some dirty air may also come in through the air filter during the intake process. While the engine oil is lubricating all the critical engine components, it also cleans by removing particles of carbon and dirt. As the oil is pumped throughout the engine, the dirty particles are screened out by the oil filter. Clean engine components help insure proper lubrication.

Engine Oil Seals
During engine operation, the pistons are rapidly moving up and down. Engine oil is also moving up and down with the pistons. Not only does engine oil lubricate, cool, and clean; it also seals between vital components. Engine oil seals between pistons and the cylinder walls to reduce blow-by. Blow-by is the gas that escapes past the piston rings and into the crankcase. Engine oil acts as a seal between components that are separated by gaskets. For example, you should put a thin film of oil on the oil filter gasket before installation to seal the connection between the filter and engine.

Understanding Oil Ratings
Reading an oil bottle can be very confusing. The three main ratings you need to become familiar with are:

• SAE – Society of Automotive Engineers
  
• API – American Petroleum Institute
  
• Energy Conserving
  

Society of Automotive Engineers
SAE rates engine oil viscosity. Viscosity is defined as the resistance to flow. Common viscosity ratings are SAE 10, SAE 30, SAE 5W30, SAE 10W30, SAE 10W40, and SAE 20W50. An oil that has two numbers in the rating is called a multi-grade oil. Multi-grade oils have been tested at various temperatures, and thus, can be used in a wide range of climates. The higher the viscosity number the thicker the oil. 5W30 oil acts like SAE 5 when cold and SAE 30 when warm. It is thin enough when the engine is cold and thick enough when the engine warms up. Light oil is used in cold climates and heavier oil is usually used in warmer climates. When the engine is cold the oil must be thin enough to get to all of the components, but when the engine warms up the oil must not be too thin as to enhance engine wear. This is why multi-grade oils have become so popular – they can fluctuate their viscosity with temperature changes. The most common engine oil viscosity rating for newer vehicles is 5W30, but always check the owner’s manual for the manufacturer’s recommendations.

American Petroleum Institute
API rates the engine oil service. SA, SB, SC, SD, SE, SF, SG, SH, SJ, SL, and SM are API rated engine oils. The first letter “S” stands for spark ignition (gasoline) engines. Sometimes you’ll see designations such as CH-4. The C stands for compression ignition (diesel) engines. The later the second letter is in the alphabet, the newer and more advanced the oil. For example, SC oil was used in vehicles in the 1960s. Newer engines are requiring more strenuous standards. When the American Petroleum Institute determines that current oils cannot meet newer engine needs or when current technology can improve engine oil qualities, it establishes a new set of standards. The key is that SM oils replace all the previous oils and can be used in any spark ignition engines with any of the previous letter designations. Look for the API symbol when identifying the correct engine oil for your vehicle. In years to come, API will come out with more advanced oil standards to replace SM oils.

Energy Conserving
Energy conserving oils have increased additives to lower friction between components. By lowering the friction, the engine becomes more efficient which in turn improves fuel economy.

Synthetic Oil
Synthetic oils are formulated from various chemicals and hydrocarbons to improve engine service and viscosity ratings. Even though synthetic oils have been used by the military since the 1950s, they became more common in the automotive sector in the 1990s. Synthetic oils have many pros and cons.

Advantages of Synthetic Oil

• Improves fuel mileage through increased lubricating qualities.
  
• Increases stability with less viscosity changes as temperatures fluctuate.
  
• Maintains lubricating qualities for up to 25,000 miles.
  

Disadvantages of Synthetic Oil

• Higher cost per quart of oil.
  
• Has a poor break in quality due to its high lubricating qualities.
  
• Usually not recommended for brand new engines.
  
• Most manufacturers still require regular oil change intervals.
  

With the various advantages and disadvantages the decision of using synthetic oil needs to be made by you and your vehicle manufacturer. It is important to check the manufacturer’s warranty when considering synthetic oils.

Oil Filters
As oil circulates through the engine, it is filtered by an oil filter. The oil filter should be replaced every time your engine oil is changed. Oil filters are composed of paper screening materials that collect dirt, dust, and other contaminants from the engine. Once the contaminants are removed from the engine oil, the oil is recirculated through the engine.

Summary
Engine oil lubricates, cools, cleans, and seals engine components. While engine oil is a vital component to the longevity of an engine and may seem extremely complex, it is not very difficult to service. When purchasing oil look for the SAE and API ratings that meet the manufacturer’s recommended requirements. Oil filters are used to remove contaminants from the engine oil.

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