ENGINE OILS

New Zealand Times, Volume LII, Issue 12211, 8 August 1925, Page 18

ENGINE OILS

AFFECTED BY TEMPERATURE . Everyone -knows that the thickness, or what is technically called the viscosity, of a lubricating oil depende in some degree upon the temperature. Thuey when the engine is absolutely cold, the lubricant in . the crankcase may he almost of the consistency of treacle, while after Some period of running the increase of temperature causes a thinning to take place, so that the oil becomes much more fluid. As, on the average, an engine will run at a lower temperature in winter than 't does in the summer, most oil companies market at least two brands of lubricant suitable for any given, type of engine, one of which' can be used in the winter and the other in the summer. These facts are mere commonplaces to the experienced motorist, but there are a few other effects caused by cold lubricant which are often overlooked. If one continues to consider the engine, it ia obvious that, to begin with, a thick oil will militate against' easy starting, by" increasing the friction between the working parts. In addition, seme oils develop a property which can best be described as gummineso after they have been used for some time, wlich causes them literally to stick, the parts- together. For these reasons it is often advisable to assist the starting motor by hand on a cold morning. HARM DONE BY “REVVING’* More important, however, js the question of what to do when the engine has commenced to run. Many people are guilty of jerking open the throttle as soon as the engine will take it, so causing the speed to mount rapidly. "While this process may not do much- harm in the case of an engine lubricated on the purely splash system, the modern power unit equipped witn an oil pump delivering lubricant through a number of more or less minute passages, can be seriously damaged by the "revving” process. Firstly, it is clear that the cold oil must be given a little time to warm up and circulate, so that if the engine is speeded up too soon there is a risk of the working parts actually rubbing against one another, metal to metal, without any protective film between them. Secondly, such an enormous strain is placed on the l pump, in endeavouring to push masses of cold, clinging oil through passages and holes, that an actual hurst may occur in the piping or the oil gauge, despite the provision of relief valves.-The correct course is to allow the engine to run slowly for some time on a small throttle opening. , . The same principles apply in some measure to the gearing in the gearbox and the hack axle. Many people take every care to warm up the engine slowly, and then proceed to drive the car An the road without a thought regarding the lubrication of the remainder of the chassis. A very thick , oil is often used in the gearbox and the back aide, and on a cold morning the gearwheels, will simply churn ohannels for themselves in the thick lubricant, and may run for quite a time witli piactically no oil on the teeth, which can but result in undue wear. Like the engine, these parts require time to warm up. EFFECTS ON THE CHASSIS ; A little care in this direction will also produce a beneficial effect! on the life of numerous other chassis parts, particularly those lubricated by grease, such' as the spring, shackles, wheel hubs, steering connections, and so on. On a cold-morning the grease in these parts will be absolutely stiff, and, until. it has melted l to some extent, the bearing surfaces will be runping in a practically dry condition. Consequently, the careful driving advocated will give the grease time to soften, and reach the surfaces before any undue loads are put upon them. This point may ,be aptly illustrated by mentioning a trouble found with the grease boxes which lubricate the axles of • goods waggons on the British railways. In several oases 'an extraordinary, degree of wear was noticed on : the axles; of waggons used Ipr short-distance goods traffic, during the winter. It was eventually found that, owing to the shortness of the-journey* and the low temperature, the grease had hot had time to melt before the truck was once agaip stationary. Consequently, the - surfaces were - running absolutely dry for the whole of their working life. , OIL OR GREASE? Of courke, the conditions are ■ somewhat different on a motor-car, hut still one is led to wonder whether the modern tendency . for the widespread use of grease is not going a little too far. Grease-gun lubrication of chassis parts is extremely convenient, and a great advance over the messy methods which at one time had to be adopted. Nevertheless, a number of motar-ejar makers still pin their faith to oil f6r. the lubrication of parts such as spring shackles, etc., .believing that, especially in cold- weather, the surfaces ate better lubricated. This accounts for the fact that on several cars the designers have retained oil cups for such parts in place of the grease connections so commonly used; and with cups of reasonable design and an efficient oil-can, the process of replenishment is certainly not unduly troublesome. However, it must be remembered that, apart from its handiness, the grease-gun system enables a pressure to he exerted which ensures that the old grease is forced away. To make sure of this in cold weather, it is as well to carry out the greasing process; immediately after the car has been funning for pome time, as the old lubricant will then be in a comparatively warm and liquid condition. Carry a. piece of tough canvas in your tool-box In an emergency it makes an excellent patch when doubler) twice and caught and held by the rim. • • • • » In additon to this waste, the presence of smoke indicates that carbon is being deposited in the combustion chamber of the engine, which in time '-ouseß knocking and impairs its power. This makes it necessary to send the machine to the rerun-- shop to have the -nrhon --'-Ti'ovcd and to have the valves rograund. j