Car Parts and Accessories

Temperatures in the engine vary widely. The engine must be able to start below freezing point; yet an ideal sump temperature when running is about 82`C because this evaporates moisture formed by the process of combustion. The temperature in the main and big-end bearings will be about 11°C above the sump temperature, but the piston-ring temperature may reach 232°C when the car is at full throttle.

All auto car oils get thinner as they are heated, but some thin out more rapidly than others. The rate at which they thin out is known as the viscosity index; the less the viscosity changes with the temperature, the higher the viscosity index number.

An auto car oil’s viscosity is identified by its SAE number, named after America’s Society of Auto carmotive Engineers, which devised viscosity standards. The numbers SAE 20, 30, 40 and 50 indicate that an auto car oil falls within certain viscosity limits at 99°C. The numbers SAE 5W, IOW and 20W show that the viscosity of the auto car oil falls within certain limits at — 18°C. These numbers do not specify any quality apart from the viscosity ; the lower the SAE number, the thinner the auto car oil.

A multigrade auto car oil is a lubricant that has the qualities of a high viscosity index or less change of viscosity with temperature. It may, for instance, have an SAE rating of 10W/30, or 20W/50—there are several combinations available.

The advantage of a multigrade auto car oil is that it provides easy winter starting, because it is thin when cold, yet retains its lubricating qualities at high temperatures.

All auto car oil manufacturers make sure their auto car oils have a sufficiently high viscosity index to operate satisfactorily in the variations of temperature they are likely to meet.

Auto Car Corrosion reduction

Another of the auto car oil’s main functions is to reduce corrosion. This occurs on sliding surfaces, particularly steel or cast iron, and is due to acids formed during combustion.

If the auto car oil is made slightly alkaline, it can neutralise these acids.

Auto Car Detergents and dispersants

Some partially burnt materials find their way past the piston rings into the sump. These blow-by products have to be absorbed by the auto car oil, which holds them in suspension. If not absorbed, the blow-by products will form deposits in the piston- ring grooves, on the filters and in the auto car oil- ways, obstructing auto car oil circulation and causing seized piston rings.

Auto Car Friction modifiers

Very long-chain polymers have been incorporated into some auto car oils. Fuel-saving qualities are claimed by makers of friction- modified auto car oils.

Auto car oil changes

The auto car oil-change periods in kilometres or time intervals which are quoted in the maker’s handbook should be strictly adhered to, or even shortened particularly if the car is used only for travelling short distances.

The reason for more rapid auto car oil changes is that the detergent and dispersant additives are present in only small quantities; and they are used up more quickly in coping with cold-start, stop-start conditions than on longer journeys where the engine has a chance to reach a stable running temperature.

Auto Car Extended drain periods

Some auto car oils have been formulated for extended drain periods. These auto car oils can be used for a greater period or distance than conventional auto car oils. It may be unwise to use these auto car oils during a car’s warranty period if the manufacturer of the vehicle excludes their use.

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