Motor oil is a type of liquid oil used for lubrication by various kinds of internal combustion engines. Other benefits of motor oil include cooling by carrying heat away from moving engine parts and cleaning and corrosion inhibition in internal combustion car engines. The major fraction of the majority of motor oils is derived from petroleum. Synthetic motor oil, consisting of artificially-synthesized compounds, currently has a minority share in the motor oil market place because it is more expensive, but offers enhanced performance. Semi-synthetic motor oil was introduced in 1966.

Use of motor oil

Motor oil is used as a lubricant in various kinds of internal combustion engines, found in automobiles and other vehicles, such as boats, lawn mowers, trains, airplanes, etc. In engines there are parts which move very closely against each other at high speeds, often for prolonged periods of time. Such motion causes friction, absorbing otherwise useful power produced by the motor and converting the energy to useless heat. Friction also wears away the contacting surfaces of those parts, which could lead to lower efficiency and degradation of the motor. This also increases fuel consumption.

Lubricating oil makes a film between surfaces of parts moving next to each other so as to minimize direct contact between them decreasing friction, wear, and production of excessive heat. Motor oil also carries away heat from moving parts, which is important because materials tend to become softer and less abrasion-resistant at high temperatures. Some engines have an additional oil cooler. It is always important to ensure all gearboxes are carrying enough oil.

In gasoline engines, the top compression ring can expose the motor oil to temperatures of 320 F. In diesel engines the top ring can expose the oil to temperatures over 600 F. Motor oils with the higher viscosity indexes thin less at these higher temperatures.

Coating metal parts with oil also keeps them from being exposed to oxygen, which inhibits their oxidation at elevated operating temperatures. Corrosion inhibitors may also be added to the motor oil. Many motor oils also have detergent additives to help keep the engine clean and minimize oil sludge buildup.

Rubbing of metal engine parts inevitably produces some microscopic metallic particles from the wearing of the surfaces. Sludge also accumulates in the engine. Such particles could circulate in the oil and grind against the moving parts, causing erosion and wear. Because particles inevitably build up in the oil, it is typically circulated through an oil filter to remove harmful particles. An oil pump, a gear pump powered by the vehicle engine, pumps the oil through the oil filter. Oil filters can be a full flow or bypass type.

In the crankcase of a vehicle engine, motor oil lubricates rotating or sliding surfaces between the crankshaft journals, bearings, and rods connecting the pistons to the crankshaft. The oil collects in an oil pan at the bottom of the crankcase. In some small engines such as lawn mower engines , dippers on the bottoms of connecting rods dip into the oil at the bottom and splash it around the crankcase as needed to lubricate parts inside. In modern vehicle engines, the oil pump takes oil from the oil pan and sends it through the oil filter into oil galleries from which the oil lubricates the main bearings holding the crankshaft up at the main journals and camshaft bearings operating the valves. In typical modern vehicles, oil pressure-fed from the oil galleries to the main bearings enters holes in the main journals of the crankshaft. From these holes in the main journals, the oil moves through passageways inside the crankshaft to exit holes in the rod journals to lubricate the rod bearings and connecting rods. Some simpler designs relied on these rapidly moving parts to splash and lubricate the contacting surfaces between the piston rings and interior surfaces of the cylinders. However, in modern designs, there are also passageways through the rods which carry oil from the rod bearings to the rod-piston connections and lubricate the contacting surfaces between the piston rings and interior surfaces of the cylinders. This oil film also serves as a seal between the piston rings and cylinder walls to separate the combustion chamber in the cylinder head from the crankcase. The oil then drips back down into the oil pan. To see these details on a crankshaft, see "How Car Engines Work" at HowStuffWorks or "Types of Lubricating Systems"at Integrated Publishing.
Automatic transmission fluid is a separate fluid. It is typically colored red to distinguish it from the motor oil and other fluids in the vehicle.

How To Change Your Car's Oil...

What you will need:
A funnel
Rags or old clothes
New oil filter
Wheel Blocks
A container that will hold 2 gallons of liquid
A wrench
4-5 quarts of motor oil
Car manual
Rubber gloves
Car jack
Jack stands

Changing your cars oil is a relatively easy process, nevertheless you should always make sure that you know what you are doing. Car makers recommend that you should change your oil every 7500 miles or so, obviously this depends on your individual driving conditions and on the car itself.

1. Park your car on a flat surface, never try to change your oil on an incline.

2. Run the car for 10 minutes before you start, this is because warm oil drains quicker and easier than cold oil.

3. Open the car's hood and place the oil on top of the engine.

4. Jack the car up so that there is enough space for you to crawl underneath, however DO NOT crawl under without first supporting the car with a pair of jack stands. You can buy these from any car parts store.

5. Block the wheels to prevent rolling.

Now you can get started...
Take the container that you want the oil to drain into as well as the wrench and crawl under your car. Find the oil drain plug on the engine and place the pan below the plug. Carefully loosen the plug with a socket wrench by turning the bolt counter clock wise. The oil will rush out and will be hot so take care!
Allow all the oil to drip into the pan then clean down the plug once it has finished.
Replace the plug by hand, then tighten it with the socket wrench. Don't overtighten it!
Find the oil filter, see the car manual if you are unsure where it is. Then place the oil pan below the filter to catch any more oil that may come out. Unscrew the oil filter using an adjustable wrench. Wipe down the rubber seal of the old filter so that it's not stuck to the engine. Attach the new filter by screwing it in using your hand, the wrench might come in handy if you aren't strong enough!

Now we need to put the new oil in...
1) Take the oil filler cap off the top of the engine.

2) Use the funnel to pour in the oil.

3) Make sure to find out how much oil you should put in by reading your car's manual.

4) When you've finished pouring the oil in and replaced the cap, turn the engine on and let the car run for 45 seconds to a minute. Check the oil level with the dipstick to see if you need to add more oil.

5) Check for leaks and tighten up the plug if necessary.

6) Once the oil has cooled, pour it into a plastic cointainer and take it to a recycling depot or an car garage who can do it for you.