History

• Shortly after inventing the wheel, Early Man figured out the friction-reducing benefits of lubricating axles with animal fat. Humans have used mineral oil for thousands of years, but its valuable ability to lubricate internal combustion engines has become exponentially more important since the advent of the Industrial Age and the subsequent invention of automobiles.
  
  Lacking adequate oil supplies, German scientists produced the first synthetic engine oils in the late 1930s and early 1940s. The use of synthetic engine oil grew in the aviation sector during the 1950s and 1960s and the first synthetic oils formulated for cars and trucks were introduced in the mid-1970s. Now car and truck owners can choose conventional engine oil or synthetic engine oil, which is more expensive but longer-lasting.
  
  

Function

• Engine oil creates a film to minimize contact between the metal surfaces of moving parts in an internal combustion engine. It also carries away metal-fatiguing heat in the engine, where temperatures can soar to from 300 degrees Fahrenheit to 600 degrees or even higher. Without oil, an internal combustion engine can overheat and seize up, a situation that often completely ruins the engine.
  
  

Types

• Different types of internal combustion engines require different types of engine oil. For instance, gasoline-powered cars and trucks use different oil than vehicles with diesel engines.
  The Society of Automotive Engineers has created a viscosity index for engine oils used in automobiles. The index measures how oil viscosity, or thickness, varies with temperature. Two common SAE classifications are monograde and mulitgrade. A monograde oil like SAE 30 can have cold-weather limitations while a multigrade oil such as SAE 10W-30 may be used in a broad range of temperatures.
  Vehicle owners should always check their owner's manual or consult with a professional when purchasing oil.
  
  

Time Frame

• The effectiveness of engine oil deteriorates over time. The oil accumulates contaminants and various additives become depleted. This explains why engine oil should be changed on a regular basis.
  Many experts recommend that automobile owners change the oil and oil filter in their vehicles every 3,000 miles. Other mechanics suggest an oil change every three or four months, regardless of miles driven. Newer cars and trucks and those using synthetic oil may be able to go longer between oil changes. Following the recommendations in a vehicle's owner manual is always sound advice.
  Remember to regularly check the engine oil level in vehicles between scheduled oil changes.
  
  

Don't Pollute

• Many vehicle owners go to a professional when it's time to change their engine oil. But a sizable number do this job themselves in their garage or backyard. Always remember to properly dispose of used engine oil. Pouring oil into the ground or down a storm sewer can pollute drinking water supplies and poison wildlife. Most cities and counties have recycling centers that will accept used oil.