Oil in splash systems is supplied by a low pressure pump, usually of the rotary type, in the base of the engine. Oil from the pump passes to the bearings, drops into the puddle, overflows through the overflow opening, and returns to the pump through a filter, the same oil being used over and over again until exhausted. This strainer should be removed occasionally and the dirt removed, for should it be allowed to collect it is likely to obstruct the oil supply. The oil should be replaced before it becomes too black or foul, the crank case and bearings thoroughly cleaned with kerosene, and new oil replaced. The supply may be interrupted by the failure of the pump, caused by sheared keys or leakage of air in the suction line due to cracks. It would be well to run the engine for a few minutes with the kerosene in the crank case, in order that all of the oil may be removed. See that the drain cock is closed at the bottom of the cylinder or all of the oil will be lost. Lock the valve handle carefully so that it cannot jar open. If light colored smoke appears in intermittent puffs with a multiple cylinder engine, it indicates that one cylinder is receiving too much oil. (117) Force Feed Lubricating System. The force feed system is by far the most reliable of all oiling systems, as it feeds uniformly and continuously at almost any temperature, and against the pressure of practically any obstruction in the pipe. The oil is supplied by a small pump driven from the engine, the pump being incased in the oil tank housing. Frequently a hand pump is used in combination with the power pump when starting the engine, or at times when the power pump is out of service. A single pump is used with any number of leads, each lead, or feed, having an independent regulating valve and sight feed, or a pump unit may be provided for each lead, depending on the size of the engine. (118) Bosch Force Feed Oiler. The force feed of the Bosch Oiler is so positive in character, that the flow of oil is not affected by heavy back-pressure due to elbows and the diameter of the conducting pipes. Springs, valves and other devices, which would check the flow of oil, are fundamentally eliminated. The amount of oil fed may be accurately and permanently regulated. Glands and other packings and bushings are eliminated. Connecting rods and all links are eliminated by the direct application of the movements of the oscillating cam disks to the pump plungers and piston valves.