AN 01-25CN-2

PARAGRAPH 6

e. COOLING SYSTEM.    (1) DESCRIPTION. - The engine is liquid cooled. A centrifugal coolant pump is mounted on the bottom of the accessory housing. The two pump outlets are connected by pipes to manifolds cast along the cylinder jackets. From these manifolds the coolant is metered by orifices to each cylinder. Individual steel sleeves direct the flow up each cylinder barrel to the hottest portions of the cylinder head. Outlets are provided on each end of the cylinder blocks. For a diagram of the coolant system, see Fig. 88. The filler cap is in the top of the expansion tank and is accessible through a door in the top engine cowl. The expansion tank contains a relief valve which opens when pressure in the system exceeds atmospheric pressure by 3 pounds, allowing a mixture of coolant and air to pass through the overflow line. A &=It check valve connecting the vent passage directly to the tank opens when atmospheric pressure exceeds tank pressure by 1/2 pound. The top forward part of each cylinder jacket is vented directly to the expansion tank.    (2) TO FILL THE COOLANT SYSTEM.-A certain amount of air will be left in the forward cylinder jackets when filling the coolant system in the three point position. Consequently the expansion tank must be filled to the top. The system will hold approximately 15.5 U. S. gallons (12.9 Imperial gallons) when filled in accordance with the following recommended procedure, which requires ten minutes. With the system completely drained, pour in the coolant, taking care that none flows into and through the overflow until the liquid rises in the filler neck. Five minutes are required to add approximately 12 U. S. gallons of liquid (10.0 Imperial gallons). Add the remaining three U. S. gallons (2.5 Imperial gallons) over a period of five minutes. Start the engine and operate until the coolant reaches a temperature of 85' C. (185' F.). Stop the engine, wait five minutes, and investigate the coolant -level. If necessary, make additions to bring it up to the proper level.    (3) REPAIR OF RADIATOR CORES.-Clean the radiator core with steam for one-half hour prior to making any repairs. The steam should pass downward into the internal passages with the radiator so placed that the condensate will drain freely from the bottom. When emergency repairs necessitate, individual tubes up to 3% of the total number may be plugged temporarily.

High-melting-point solder must be used for the repair of cores. This solder requires the use of a radiator torch. The temperature at which this solder is applied should not exceed 450°C. (8500 F.). To replace tubes and to make any other radiator repairs with solder, zinc chloride flux only should be used for cleaning, and the solder should be flowed by the use of a torch.    (4) REPAIR OF COOLANT TANK.-Clean and repair coolant tanks as outlined in this Section on the repair of the oil tank. Test the coolant tank after repairs under water to 20 p.s.i.  f LUBRICATING SYSTEM.    (1) DESCRIPTION.      (a) Oil flows from the bottom of the oil tank through a line in which is incorporated the "Y" drain cock, to the oil inlet connection on the engine, where it is circulated by one pressure and two scavenging pumps of the simple gear type. The pressure and main scavenging pumps are arranged in the unit at the right of the accessory housing. The oil supply is delivered from the oil tank to the pump. Then it passes to the exterior of the "Cuno" strainer, through a check valve, which is arranged to prevent oil entering the stopped engine from the oil tank unless a head of 3 psi. is exceeded. The "Cuno" strainer is equipped with a safety-by-pass valve set to open at a pressure drop exceeding 100 psi. Oil pressure at the outlet of the "Cuno" strainer is transmitted to the piston of a spring-opposed relief valve, which by-passes excess oil directly from the outlet to the inlet of the pressure pump. This arrangement maintains a constant oil pressure at the strainer outlet, with increasing strainer restriction, within the limit of the pump capacity. The relief valve is accessible for cleaning or adjusting to change the oil pressure, without removal of the oil pump. (See Fig. 89.)      (b) The oil tank is located aft of the firewall and forward of the artner plate installation at Station 2 and is accessible by removing the fuselage cover between the firewall and windshield. The oil tank contains a hopper which keeps the oil in circulation and returns the same oil to the engine without mixing the oil with all the oil in the tank. This is an aid in warming up the engine and also helps in oil dilution. The tank capacity is 8.75 U. S. gallons (7.3 Imp gallons).

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