Design and Application of Thermostats to the Cooling System of the Internal-Combustion Engine

Abstract

The history of the thermostat is shown and the way in which effective engine-coolant temperature control has been obtained through the years. The main reasons for the use of thermostats are as follows: (1) Lower engine wear. (2) Improved thermal efficiency. (3) Requirements of the modern car heater. The basic design requirements for the ideal engine thermostat are then enumerated. The paper discusses how near the modern thermostat comes to these requirements. The poppet type and butterfly type valve are used for thermostats, the advantages and disadvantages of each type being discussed. The main problem is dirt, which becomes trapped in the valve seating, and increases the warm-up time of the cooling system. The design features of the bellows type and wax type thermostat, and the fillings used in the bellows type are discussed. The damping of vibration periods by hydraulic and friction methods are shown. The wax type thermostat has gained popularity because of its insensitivity to pressure when the coolant system is pressurized. The heat transfer of the wax pellet is slower than the vapour in the bellows type, and the reasons for this are given. Thermostat installations are discussed and illustrated.