THE CHOICE OF OILS.

Auckland Star, Volume LXI, Issue 123, 27 May 1930, Page 19

THE CHOICE OF OILS.

IMPORTANCE OF SELECTION. Out of the gallon or two of lubricating oil that is put into the crankcase of a motor, there is actually not much more than a thimbleful working at one time. This thimbleful consists of the thin film that lines the cylinder walls, keeping the pistons sailing up and down, and prevents the journals from wearing against the bearings. Yet this tiny amount must be viscous enough to remain intact during the lubricating process, but must not be so heavy or thick as to cause a drag upon the moving parts. It takes a very efficient oil to be able to withstand the high explosion temperature in the cylinders of motors. This temperature rises to about 2SOO degrees Fahrenheit, enough to melt platinum, and onlv a good viscous oil can keep from breaking its film and cause scoring of cylinders and leakage of gases under this continuous battery. Professor A. M. Low, the great English physicist, says that oil must not be very stiff when cold, in order to enable the'moving parts of the engine to operate without hindrance; neither should it be watery when hot. It must not readily combine with the benzine that happens tb leak past the piston rings, nor must it form a watery sludge with any of the condensed steam from the burnt gases that leak into the crankcase. "Even the best polished cylinders are composed of a number of small lumps and dents when viewed through the miscroscope," he says, "and these must be filled up and 'excused' by the oil." That points to the necessity of having good oil at all times in the crankcase. Every manufacturer knows exactly what kind and grade of oil is best for his motor. His advice should be followed religiously if one wants to keep the engine running properly. Even the same type of motor may require a different oil for lubrication than that recommended for it by the manufacturer, due to its age or other conditions. The dealer or service man who has worked on it can tell what this should be. Usually a lighter-grade of oil is needed for winter because cold tends to stiffen it. Stiff oil means that the pistons scrape along the raw sides of the cylinders during the first explosions of the motor, without benefit of the necessary film to afford smooth operation and prevent scoring of the walls. It also means hard starting, sometimes so hard that it is difficult for the electric starter to turn over the motor. Too light an oil, on the other hand, even in cold weather, means liability of broken films of lubricants along the cylinder walls, when the motor has heated up and when this film is needed most for lubrication. It is, therefore, very important to know exactly what grade of oil is best for the car at all seasons of the year.