MOTORING.

Press, Volume LXI, Issue 18526, 30 October 1925, Page 6

MOTORING.

ENGINE OIL, COLD LUBRICANT EFFECTS. GREASING THE CHASSIS. Everyone knows that the thickness, or whaA is technically called the viscosity, of a lubricating oil depends in some degree upon the temperature. Thus, when the engine is absolutely cold, the lubricant in the crack case may be almost of the consistency of treaclfe, 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 it 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 tho winter and the other in the summer. These facts are mere commonplace to the experienced motorist, but there are a few other effects caused by cold lubricant which are often overlooked. "Consider the Engine, If we continue to consider the engine, it is obvious that, to begin with, a thick oil will militate against easy starting, by increasing the friction between the working parts. In addition, some oils develop a property which can best be described as gumminess after they have been used for some time, which causes them literally to stick fJie parts together, For these reasons it is often advisable to assist the starting motor by hand on a cold morning More important, however, is the question of what to do when the engine has commenced to run. Manj people are guilds of jerking open the throttle as soon as the engine will take it, bo causing the speed to mount rapidly. While this process may not dp much harm in the case of an engine lubricated on the purely splash system, the modern power unit equipped with an oil pump delivering lubricant through a number of more or lesa minute passages, can be seriously damaged! by the "revving" process. Colli Oil Most be Wajpmed. First, it is clear thai, the cold oil must be given, a little time to warm up and circulate, so tha£ if the engine is speeded up too swjq there is a risk of the working actually rubbing against one aether, metal to metal, without any protective film between them. Second, such an enormous strain fs placed on the pump, in endeavouring to push masses of cold. Clinging oil through passages and holes, that an actual burst may occur in the piping or the oil gauge, despite the provision of relief valves. The cor rect 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 t£p gearing in the gearbox and the back axle. Many people take every car© to warm up the engine slowly, and then proceed to drive the car sin 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 &xle and on a cold morning the gearwheels will simply churn channels for themselves in the thick lubricant, and piay run for quite a time with practically no oil on the teeth, which can but result in undue wear. Like the engine, these parts require time to warm up. A little care in this direction will also produce a beneficial effect oc tho life of numerous other chassis parts, particularly those lubricated by grease, such aa the spring shackles, wheel hubs, steering connexions, and'so on. On a cold morning the grease in these parts will be absolutely stiff, and, until it has melted to some extent, the bearing sutfacee will _be running in a practically dry condition. Consequently the careful driving advocated will give the grease time to soften and reach' the surface before any undue loads are put upon them. Tfonbte to Grease Boxes. 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 6everaJ cases an extraordinary degree of wear was notic**!) on s the axles of waggons used for short-distance goods traffic, during the winter.' It was eventually found that, owing to tlw shortness of the journcy and tihe lpw temperature, tho grease had! not had time to melt before the truck was onoe again stationary. Consequently, the surfaces were running absolutely dry for the whole of then working life. Of course, the conditions are somewhat different on a motor-car, but 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 motor-car makers still pin their faith to oil for the lubrication of parts such as spring shackles, etc., believing that, especially in cold weather, the surfaces are bettor lubricated. OU Cups Eetained. : This accounts for the fact that on several cars the designers have retained oil cups for such parts in place of the grease connexions so commonly used, and with pups of reasonable design and an efficient oilcan, the process of replenishment is certainly not unduly troublesome. However, it must be remembered that, apart from its liandiness, the grease-gun system enables a pressure to be 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 running for some time, as the old lubricant will then be in a comparatively warm and liquid condition.