1942 - 1947 Chevrolet Shop Manual



0-6

Figure 1 shows the data in the above tables as it would appear on a thermometer-the lowest temperature at which the		engines, such as the Crankcase ventilating system, have greatly lengthened the life of good lubricating oils. However, to insure continuation of best performance, low maintenance cost and long engine life, it is necessary to change the Crankcase oil whenever it becomes contaminated with harmful foreign materials. Under normal driving conditions draining the Crankcase and replacing with fresh oil every 2000 to 3000 miles is recommended. Under the adverse driving conditions described in the following paragraphs, it may become necessary to drain the Crankcase oil more frequently. Driving over dusty roads or through dust storms introduces abrasive material into the engine. Carburetor Air Cleaners decrease the amount of dust that may enter the Crankcase. The frequency of draining depends upon severity of dust conditions and no definite draining periods can be recommended. Short runs in cold weather, such as city driving, do not permit thorough warming up of the engine and water may accumulate in the Crankcase from condensation of moisture produced by the burning of the gasoline. Water, in the Crankcase, may freeze and interfere with proper oil circulation. It also promotes rusting and may cause clogging of oil screens and passages. Under normal driving conditions this water is removed in the form of vapor by the Crankcase ventilator. But if water accumulates, due to short runs in cold weather, it should be removed by draining the Crankcase as frequently as may be required. It is always advisable to drain the Crankcase only after the engine has become thoroughly warmed up or reached normal operating temperature. The benefit of draining is, to a large extent, lost if the Crankcase is drained when the engine is cold, as some of the suspended foreign material will cling to the sides of the oil pan and will not drain out readily with the cold, slower moving oil. CRANKCASE DILUTION A phase of engine oil deterioration, probably the most serious of all, is that of Crankcase dilution. By Crankcase dilution, we mean a thinning of the oil due to certain portions of the gasoline leaking past the pistons and rings and mixing with the oil. Leakage of gasoline, or gasoline vapors, into the oil reservoir mostly occurs during the "warming-up" period when the gasoline is not thoroughly vaporized and burned.
	indicated grades of oil will permit easy starting. When in doubt use the lighter grade of oil. NOTE-The use of 20-W is recommended rather than S. A. E. No. 20 if you anticipate temper-atures to drop to freezing. Summer The use of 20-W, or S. A. E. No. 20 during the summer months will permit better all-around performance of the enine than will the
	heavier body oils with no appreciable increase in oil consumption
Fig. 1—Lowest Starting Temperature for Oils Indicated
If S. A. E. No. 20 or No. 20-W oil is not available, S. A. E. No. 30 oil may be used if it is expected that temperatures will be consistently above 90 degrees F.
MAINTAINING OIL LEVEL The Oil Gauge Rod (Fig. 2) is marked "Full" and "Add Oil." These notations have broad arrows pointing to the level lines. The oil level should be maintained between the two lines; neither going above the "Full" line nor under the "Add Oil" line.
Fig. 2—Oil Gauge Rod	Check the oil level frequently and add oil when necessary. Always be sure the Crankcase is
full before starting on a long drive.
WHEN TO CHANGE CRANKCASE OIL Some oils have been greatly improved, driving conditions have changed, and improvements in