Viscosity is an internal friction or resistance to a liquid current. During the winter period of operation it is necessary to apply маловязкие engine oils which provide easier start-up of the engine at maintenance of necessary lubricant properties. During the summer period of operation it is preferable to apply more viscous oils.

System SAE (Society of automobile engineers of the USA). In an oil designation two degrees of viscosity are specified: winter with the letter W and summer without a letter designation, for example SAE 5W-30. The less first, the better fluidity of oil at low temperatures. The above the second, the above firmness of oil to heats.

System ACEA (noncommercial Association of automobile engineers). The system operates since 1996 and has replaced system SSMS. The class is applied To petrol engines And, for diesel — a class of Century

System SSMS (noncommercial Committee of designers of cars). The oil designation consists of the letter G (the petrol engine) or D (the diesel engine), and also one number. For example, ССМС G4. The above the number, the is better quality of engine oil.

System API. At a designation of oils are present or the letter S (the petrol engine), or "With" (the diesel engine), and also the subsequent letters. For example АРI-SA and API-CA. The above the letter alphabetically the following after letters S or "With", the above quality of oil.

Fig. 167. "Ford" recommends engine oil viscosity SAE 5W-30

Ford for cars Focus with petrol engines recommends engine oil SAE 5W-30, and also ACEA A1/B1, WSS-M2C912-A1 and WSS-M2C913. For diesel accordingly WSS-M2C913-A or WSS-M2C912-A. Do not apply some oil to petrol engines with designations API SC, SD, SE or SF (diesel engine API CC), they can damage to the engine (fig. 167).

Try not to mix some oil of different manufacturers, especially at all do not mix the oil intended for the petrol engine, with oil for the diesel.