1942 - 1947 Chevrolet Shop Manual



	0-7

		Short runs in cold weather, such as city driving, do not permit the thorough warming up of the engine nor the efficient operation of automatic control devices. It is recommended that the oil be changed more often when the car is subject to this type of operation. The car should be kept in good mechanical condition. Poor mechanical condition of the engine, such as scored cylinders, poor ring fit, "sloppy" or loose pistons, faulty valves, poor ignition and incomplete combustion will increase Crankcase dilution. A good grade of gasoline should be used. Poor gasolines which contain portions hard to ignite and slow to burn will increase Crankcase dilution.

	Fig. 3—Crankcase Ventilation Automatic Control Devices to Minimize Crankcase Dilution The Chevrolet engine is equipped with automatic devices which aid greatly in minimizing the danger of Crankcase dilution. Rapid warming up of the engine is aided by the thermostatic water temperature control, which automatically prevents circulation of the water in the cooling system until it reaches a pre-determined temperature. Thermostatic heat control on the exhaust manifold which, during the warming-up period, automatically directs the hot exhaust gases against the center of the intake manifold, greatly aids the proper vaporization of the gasoline. The down-draft carburetor is an aid to easy starting, thereby minimizing the use of the choke. Sparing use of the choke reduces danger of raw, or unvaporized. gasoline entering the combustion chamber and leaking into the oil pan or Crankcase. An efficient Crankcase ventilating system drives off gasoline and other vapors and aids in the evaporation of the raw gasoline and water which may find its way into the oil pan or Crankcase. Fig. 3. Control by Car Owner under Normal Conditions Ordinarily the above automatic control devices will minimize, or eliminate, the danger of Crankcase dilution. However, there are abnormal conditions of service when the car owner must aid in the control of Crankcase dilution.	Water in Crankcase Serious lubrication troubles may result in cold weather by an accumulation of water in the oil pan. This condition is, as a rule, little understood by the car owner. To demonstrate the chief cause of water in the oil pan, hold a piece of cold metal near the end of the exhaust pipe of the engine and note the rapid condensation and collection of drops of water on it. The exhaust gases are charged with water vapor and the moment these gases strike a cold surface, will condense, forming drops of water. A slight amount of these gases passes the pistons and rings, even under the most favorable conditions, and causes the formation of water in the oil pan, in a greater or less degree, until the engine becomes warm, When the engine becomes thoroughly warm, the Crankcase and oil pan will no longer act as a condenser and all of these gases will pass out through the Crankcase ventilator system. Short runs in cold weather, such as city driving, will aggravate this water-forming condition.
		Corrosion Practically all present day gasolines contain a small amount of sulphur which, in the state in which it is found, is harmless; but this sulphur on burning, forms certain gases, a small portion of which is likely to leak past the pistons and rings and reacting with water, when present in the oil pan, form very corrosive acids. The more sulphur in the gasoline, the greater the danger from this type of corrosion. This is a condition which cannot wholly be avoided, but it may be reduced to a minimum by proper care of the engine. As long as the gases and the internal walls of the Crankcase are hot enough to keep water vapor from condensing, no harm will result; but when