In the winter base your choice must be the lowest temperature you expect, and in the summer base the highest. The narrowest span with a more heavy base is better if your temperature zone allows, cause a wide span means more polymers, and more polymers are not good for your engine.

The other known classifications are:

API (American Petroleum Institute) Classification:

Engine oil performance is expressed by two letters. The first letter indicates whether the oil is for gasoline (S) or diesel (C) engines. The second letter specifies the level of technical performance within the relevant group: A for the minimum level for both gasoline and diesel, and J (gasoline) and F (diesel) for the highest level.

• Gasoline: (min. performance) SA..SB..SC..SD..SE..SF..SG..SH..SJ (max. performance)
• Diesel: (min. performance) CA..CB..CC..CD..CE..CF (max. performance)

ACEA (Association of European Car Manufacturers) Classification:

Oil performance is described by a letter followed by a number.

ACEA standards are divided into three categories:

• A for gasoline engines,
• B for diesel car engines,
• E for diesel engines for commercial vehicles and trucks.

Levels of lubricants performance are expressed by a following number:

• 1 for fuel-economy oils
• 2 for general purpose oils, and
• 3 for high performance oils

Example: A1 describes a fuel-economy gasoline engine oil, and A3 describes a high-performance gasoline engine oil.

The proper viscosity grade to use depends on many factors such as ambient temperature, miles on the engine, bearing and piston clearances, and type of service. A general rule of lubrication is to use the lowest viscosity possible which will provide the proper separation of metal. Anything more than this minimum will increase power loss due to friction and will reduce the pumpability of the oil at all temperatures. However, one must consider synthetics differently when determining viscosity requirements.

Mixing Synthetic Oil with Other Type

It is said synthetic oil is compatible with the conventional mineral oils, thus it is safe to mix two different types, but for sealing purposes and the final performance of your engine I suggest you choose one at the beginning (i.e. Synthetic oil), and never change your oil type.. It is known that the content of mineral oils are different than synthetic oil, and mineral oil soaked gaskets and seals have been known to leak when exposed to synthetic oil. So, you may think using flushing oil first, before switching another type as some people suggest. Yes, the flushing oil removes all the deposits and dissolves all the mineral oil deposits in your engine and you may think everything is OK for switching to synthetic oil, but using a thin oil for flushing may remove deposits that built-in time and work for sealing your rings and gaskets. It is known that engines over 250,000 km worked without a problem, but when flushed it failed in a month. So choose one at the very beginning, flush your engine if necessary, and never change the oil type. Only move to a different weight in the same type, if it's necessary because of a considerable change in temperature zone, cause the viscosity must be adapted to the conditions in which the vehicle is used, the environment and the climatic conditions.

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