The real oils your car needs all year

Press, 23 September 1988, Page 39

The real oils your car needs all year

CARS

One of the best ways of prolonging engine life is to regularly change the oil. It is often too easy to let the mileage drift past a scheduled change, leaving your engine circulating dirty and damaging oil. Oil has a good many jobs to do in an engine, and failing to carry out regular changes exposes your engine to serious dangers. Oil. must keep the engine lubricated and help cool it. It must also keep the engine as clean as possible by minimising the amount of sludge which forms, and preventing engine parts from tarnishing. The oil must carry out these functions at extremes of temperature throughout its life. Modern motor oils are capable of meeting these needs, but it is important to realise that oil will not continue to perform indefinitely.

The oil’s base will eventually start thickening because of oxidation at hot operating temperatures. Additives put in the oil by the manufacturer will either be used up or lose their effectiveness. Few will quibble about the advantages of long oil life. But the biggest cost savings come in giving

your engine long life. Regularly changing the oil is a simple cost-effec-tive way of minimising wear and prolonging engine life. A potentially damaging waste product from an engine is heat. Cars, of course, have a cooling system to cope but this can only do so much. About two-thirds of waste heat is absorbed by the fluid in the cooling system, the air and expelled gases. Up to a third of the waste heat can be absorbed by the oil, particularly round high-stress bearings. If oil did not carry this heat away from the likes of the main bearings and big-end bearings, they would quickly overheat and fail. Oil, however, is like any other car component. Heat will see it deteriorate. In difficult conditions, oil pooling in an engine

sump can reach 150 degrees. Round the pistons, it can reach nearly 300 degrees. Oils have anti-oxidants added to reduce the rate of oxidation at higher temperatures. Round-town running also has its share of dangers for oil. Short trips do not usually allow the oil to reach normal operating temperatures. This can encourage sludge-forma-tion. Dispersants are added to oil to help keep these minute particles in suspension. This is no problem. The oil will blacken fairly quickly, but its lubricating properties will not be affected. As long as the oil holds the sludge in suspension, it will be drained out at the next change. Leave the change for too long and you overburden your oil. The sludge

begins to form engine deposits which can block filters and oilways, raising the chances of starving bearings of oil. Repairs will be costly. Round the pistons, where extreme temperatures are created, there is the risk of carbon-like deposits round the rings and tarnishing round the pistons. Detergents are added to oil to prevent these buildups. Ageing oil will be less effective at keeping such deposits from forming. Carbon deposits building round the rings reduce lubrication in the area, cause-them to stick in their grooves and possibly lead to a breakage. Oil reduces wear by forming a coating over moving parts exposed to friction. In most engines oil does not get pumped to bearings until the engine is started. Therefore, there can be some metal-to-metal contact when starting a car.

Such rubbing is also possible when running in an engine while tiny irregularities in bearings are smoothed out. Car makers specify a particular grade of oil for an engine. This specification is the result of months of testing and monitoring of engine performance and temperatures. Varying the manufacturer’s recommendation can be risky. Using an oil which is too thin could see it unable to coat bearing surfaces completely. This will create rapid wear. Oil is an essential element in keeping corrosion within the engine to a minimum. Little corrosion actually- occurs when a car is running. Most occurs when a car is not in use, which is usually more than 90 per cent of its life. As engines cool, combustion products form acids with water, a by-

product of petrol combustion. Additives are mixed with oil to reduce the formation of these corrosive chemicals. Some oils are thicker than others. SAE numbers are used to describe viscosity. SAE 10W, SAE 20W, SAE 30, SAE 40 and SAE 50 are commonly used for engine oils. SAE 10W is the thinnest of these examples. Each SAE rating defines the oil viscosity. Those with a “W” after the figure are measured at — 17.8 deg, while those without the “W” are measured at 98.9 deg, near the boiling point of water. Oils thin as they get hotter and thicken as they cool. Oils thicken and thin differently depending on their make-up. The SAE system can be used to describe viscosity-tem-perature relations by combining the numbers to indicate multigrade oils. Therefore, we can have

an SAE 10W/30, SAE 20W/50 and the like. Most car makers specify the use of a multigrade oil year round. An oil with an SAE rating of 10W/50 can therefore be expected to give the best of both worlds. It will be thin at cold temperatures, allowing it to circulate rapidly through the engine and quickly coat bearing surfaces. Yet, with its topend SAE 50 rating, it will remain thick enough to ensure adequate lubrication even under the most trying conditions.

Oil is an essential part of your engine. It performs an array of functions yet requires only the simplest of upkeep. Regularly check your car’s oil level, change the filter at the recommended intervals and never ignore the need for an oil change. It will otherwise be costly in the long run.