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Lubrication 3 - Oil

Lubricating oil should be, even in a cold state, a very thin liquid to make the work easier for the starter . At the same time the oil film must always remain intact to protect any sliding bearings and should nonetheless reduce the internal friction in the engine to a minimum. Because lubricating oil becomes hotter than the coolant when the engine is in use and more easily reaches heat sensitive parts, does it play a very important role in cooling the engine, particularly if the oil filter is in an airflow, or if there is an additional oil cooler or an oil-coolant heat exchanger (see picture with coolant connections).

Oil is obtained in the refinery by vacuum distillation. Lubricating oil contains, beside the components which are directly won from crude oil, other additives for different desired qualities. Thus, it should prevent the deposition of pollutants, neutralise acids and adapt itself through its viscosity to the needs of the engine. Nowadays almost exclusively, multi-grade oils are used for engines (e.g., 10W-40). They are thin when cold and thicken with warmth, which makes them more suitable than single-grade oils (e.g., 30W-30). This is achieved through long-chained molecules (polymers). The low amount of movement of the oil molecules at low temperature is not as strongly hindered as the stronger movement at high temperatures, which makes the oil appear to be thicker.

Synthetic oils (e.g., 0W-40) have a lower viscosity in all ranges without the risk of the oil film breaking down. The advantages are, lower internal friction, a slightly lower fuel consumption and slightly better performance. Synthetic oils can be used in the engine if agreed to by the manufacturer. Whether or not mineral oil was previously used, is not important because all engine oils are mixable with each other (HD standard). Of course, the properties of the various oils mix with each other according to the mixing ratio.

Transmission oils are classified as 'Gear Lubricant', from GL1 to GL5. Whereby GL3 is used for manual transmission and axle gearboxes, GL4 ist prescribed for those having hypoid gearing. Should an exceptional amount of strain also be present, then GL5 is necessary.

Hydraulic oils may also be dyed for identification purposes, e.g., red for ATF oil. Apart from circulating in automatic transmissions and torque converters (formerly hydraulic clutch), it is also found in trucks as a retarder (3rd brake).

Engine oils, gearbox oils and used oil filters should be stored apart from other waste and be collected by specially equipped companies to be reprocessed. One distinguishes between waste oil of both known and unknown origin. Known origin can only be claimed if the workshop itself has removed the oil. ATF oils used in automatic gearboxes can contain PCB and must be disposed of as hazardous waste.
Lubricating oils (like diesel) are classified in the danger class AIII and must therefore, also be stored in special containers or rooms.

Some vehicles, e.g., motorcycles, campers or veterans are often temporarily taken out of service. In this case an oil change is recommended immediately before the lay-off period. Engine oil is also subject to an ageing process. In the engine it has contact with oxygen and can decompose with time and can also attack metals.

If black oil sludge becomes visible after removing the the valve cover, an oil and oil filter change, if it has not recently been carried out, is indicated. White oil sludge indicates predominantly short distance driving where the engine often did not reach the operating temperature. The customer should be advised accordingly. 08/11

Overview of the API-classification

Is being increasingly replaced by ACEA(Association des Constructeurs Européens de l' Automobiles)

Service-classes (Internal combustion engines)

SA: Oils for light operating conditions
SB: Additives against wear and tear and oxidation
SC: Petrol engines from 1964 - 1967
SD: Petrol engines from 1968 - 1970
SE: Petrol engines from 1971->
SF: Petrol engines from 1981->
SG: Higher piston cleanliness, lower cold sludge and varnish developement
SH: Higher demands (with energy conservation using light-running oils and with strict product supervision)
SJ: Higher demands for energy saving for low visosity oils (0 W-20, 5 W-20, 10 W-30).
Higher standard to protect the Lambda-sensor on the catalytic converter. Introduction of new test methods for the measuring of the resistance to foam development, jellifying, heat and oxidation.

Commercial-classes (Diesel engines)

CA: Light operating conditions
CB: Medium load
CC: Medium to heavy load
CD: Specially for charged Diesel engines
CE: Maximum loaded and fast running Diesel engines, with- or without charging and with strongly varying loads
CF: Newer version of the CD-specification