What does Motor oil do?
To put it simply your engine is composed of lots of moving parts that create friction and heat. Motor oil is used as a lubricant to reduce the friction and heat. Running your vehicle with low or no oil will cause excessive heat to build up which breaks down metal parts which then can blow the motor.
Synthetic Versus Conventional
Conventional lubricants are made from crude oil. It is removed from the ground and then refined to remove impurities. It then is blended with chemicals and bottled for sale. But even through the refining process there are still a lot of in solubles such as, paraffin, waxes, silicon, and dirt and other natural contaminants. These substances can leave behind residue on the engine and cause a build up allowing heat to settle in. Another problem conventional oil has is that it is not stable at different temperatures. It tends to thin out when it gets really hot and thickens when it gets cold.
Synthetic oils are usually man made and derived from natural gas or alcohol. This makes them purer containing no undesirable contaminants. Little to no residue is left behind and the lubricant has more of an even temperature regardless of the weather. Synthetic oil is far better at transferring heat thus leaving the engine much cooler.
Another thing to consider when deciding which oil to go with is that conventional oil should be changed every 3000 miles because it breaks down where as synthetic oil can go 5000 miles before breaking down. Synthetic oil can also be significantly more expensive then conventional oil. You will have to decide if going longer between maintenance periods and prolonging the life of your engine is worth the extra expense.
Myth!- It is commonly thought that if you have an old car or high mileage you should not use synthetic oil. This is NOT true! If anything older vehicles especially with high mileage need the better lubricants to keep them running longer.