All engine oils come in varying viscositys. Viscosity is the resistance to flow that the oil has, therefore a lower number means easier flowing oil. Higher viscosity oils are thicker than lower viscosity oils. All oils flow slower at colder tempatures.
Their ratings come in two basic types. Single grade and Multi Grade. Single grades are called straight weight motor oils. Example of a typically labeled straight weight motor oil: SAE30. It is not commonly used in todays vehicles due to cold weather conditions.
Multi-grade oils are typically labeled as all season oils and an example is: 5w-30. The first number is the viscosity of the oil when cold, and the second number is at normal tempature. That may sound confusing at first since all oils flow slower when cold, but the number is smaller in that instance. Let me explain...
A 5w-30 weight oil when cold has a viscosity rating similar to SAE5 cold (cold is the most important word). SAE5 cold has a slower flow rate than SAE30 does hot. The effect of coldness on the oil is a huge effect as you can see. Once the 5w-30 oil is warmed up, it will flow at the rate of SAE30 hot. This multi-grade oil allows easier starting in cold winters and still offers thicker protection once the engine is hot.
People always ask me if they should use 10w-30 or 5w-30. Obviously 5w-30 is better for cold climates, but otherwise it makes no difference. That is why most vehicles now just recommend 5w-30 instead of the other. Mobile1 now has a new oil out that is 0w-30 that is perfectly fine and healthy for use in most cars.
Typical weights used today.
0w-30 5w-30 10w-30
20w-50 - Diesel or old cars/trucks
You can actually put thicker oil in an older engine to help hide or get rid of ticking noises and oil consumption issues. If you have ever used Lucas Oil, you would understand how thick oil could get rid of oil leaks. As an engine ages, the clearance gaps in engine parts can become enlarged and a thicker oil may be needed to properly lubricated the engine.
Thinner oils are being used in todays vehicles as thinner oil is easier to pump and easier for the mechanical parts to move in. Thinner oils can save your engine more horsepower, and increase gas mileage. I DO NOT recommend putting a thinner oil than reuired into your vehicle as engine damage may occur.
So in conclusion, the choice is your when it comes to using synthetic oils, conventional oils, or settling in between. Just keep in mind, always change your oil regularly as advised by the vehicle manufacturer. Some recommend oil changes every 3,000 miles while others may recommend it only after 30,000 miles. Consult your owners manual.
There are many different types of oils on the market. They all offer certain amounts of protection, varying price, variable viscosity, and different levels of efficiency. Their main purpose is to be used as a lubricant, but also as a way to cool engine components. I am going to try and explain as simply as possible the current types of engine oil that get used in the automotive field.
Synthetics are man produced oils derived from modified petroleum elements or other raw ingredients. They offer superior protections in all climates and engine operating conditions. Synthetic oils have several advantages and only one disadvantage - cost. They are extremely pricey when compared with natural or blend products.
Synthetics generally last longer. They do not break down as quickly as regular oil. Also, their molecules are all exactly the same size and conventional are not. That is the theory behind why switching to synthetic on an old vehicle will cause excessive leaks as the different sized molecules wont clog up the hole - but recent studies have determined there is little effect. I do not condone this statement, but rumor has it that "Synthetics have been rumored to last for several thousand miles (example 12K) as long as you change the filter."
Regardless of the type of oil used, always change them regularly based on manufacturers recommendations. The additive packs in oils are what fails after a short while.