Document Ra577y9GJk2Qx6kjr00ooLRrn

NAPA AUTOMOTIVE CAREER TRAINING Automotive Thermostat - Continued Car manufacturers now specify thermostats which are not sensitive to pressure and which are not affected by changes of cooling system pressure. Car manu facturers also specify thermostats with "reversepoppet" valves. Coolant under water pump pressure is used to help hold a closed reverse-poppet valve tightly closed in order to prevent leakage. A reverse-poppet valve opens against water pump pressure, against the direction of coolant flow. Before 1958 it was common practice to use thermo stats opening at 160F, in hot weather, changing to another thermostat which would open at 180F. during cold weather. This practice has been unneces sary since cooling systems have been designed to operate under pressure. Starting about 1958, all passenger car engines were made with thermostats opening at 180F. About 1962 American Motors and Ford started to use thermostats opening at 190-195F. All engines in popular cars made since 1969 have been equipped with thermostats specified to open at about either 190F. or 195F. These thermostats will be fully opened at 212F, and they will control the temperature of coolant leaving the thermostat and going into the top tank of the radiator at about 200-205F. Radiator hose, like the other parts of the cooling system, is put under tremendous amounts of stress. The average modern engine cooling system must be able to withstand at least 16 lbs. of pressure, com bined with underhood temperatures that can range up to 278F. To provide adequate cooling under these conditions, the cooling system may have to circulate as much as 7,500 gallons of coolant per hour! Radiator hose must do its part of the engine cooling job effectively. Otherwise, loss of coolant due to hose failure may cause the engine to overheat and internal engine damage may result. The Rule For Thermostat Application Always recommend as a replacement, a thermostat which opens at the same temperature as the ther mostat originally installed in the engine and as speci fied in the car manufacturer's shop service manual. HOW RADIATOR HOSE IS BUILT TO LAST Cooling systems in all modem passenger cars require radiator pressure caps in order to prevent coolant from boding due to today's high engine operating temperatures. Radiator pressure caps and their effect on boiling will be discussed in the radiator cap section. Ethyleneglycol based "Coolant" or "AntiFreeze" is recommended for use to help prevent boiling. A radiator hose is composed of three basic com ponents: the tube, a hollow cylindrical section of rubber; reinforcement, usually yarn, fabric, wire, or a RADIATOR HOSES combination; and a cover. The function of the tube is The upper and lower radiator hoses serve as flexible to withstand the corrosive, abrasive, and other connections between the radiator and the rest of the properties of the coolant being transmitted. The engine cooling system. Vibration and movement reinforcement is the "muscle" of the hose. It is the between the radiator and engine could cause breakage part that gives the necessary strength to resist the of rigid pipes, and for this reason a flexible con internal pressure. The cover protects the reinforce nection is needed. ment and tube from the environment. These 14