SAFARI

ENGINE 123 Fig. 1 ENGINE COOLING SYSTEM THERMOSTAT Fig. 1. Thermostat installed in cooling system between upper cooling water line and radiator upper tank ensures minimum operating temperature of engine which is extremely important for efficient engine operation and longer engine life. So long as engine is cool (immediately after starting) thermostat does not allow water to go to radiator thus disconnecting it from cooling system. Water flows towards water pump through by-pass out-let of thermostat and is circulated back to engine, short circuiting radiator. Thus, working temperature of engine is achieved rapidly. As soon as working temperature of engine is attained, thermostat valve starts gradually lifting, allowing cooling water from-engine to circulate through radiator. At the same time by-pass out-let to water pump gradually closes’ thereby allowing only metered quantity of cooling water to flow through it. Thermostat is self-controlled to adjust water flow quantities through radiator and bypass outlet in accordance with engine working temperature. Failed thermostat keeps valve in open position and is as good as an engine operating without thermostat. This will result in over-cooling of engine, particularly if vehicle is used for short distance runs, or operates in city. Although adverse effects of over-cooling on engine operating without or with failed thermostat may not be visible immediately, engine life and its operating efficiency are decisively affected. Therefore, do not operate engine without or with a failed thermostat. CHECKING OF THERMOSTAT 1 Fix thermostat on test stand. 2 Fit a dial gauge connecting its spindle to thermostat valve diaphragm through pointer. 3 Adjust pre-load on dial to about 0.5 mm and set dial gauge needle at zero. 4 Place test stand with thermostat in a vessel filled with water over a burner. 5 Place suitable thermometer (preferably calibrated telethermometer) into water. 6 Note down temperature when dial gauge needle starts moving indicating opening of valve (opening temperature). 7 Simultaneously note down temperature when valve is opened to 7.5 to 8.5 mm (fully open). (Max. lift of value 8 + 0.5 mm for DICOR Engine.) 8 For DICOR engine thermostat opening temperature 83 + 2 0 C fully open at 94 0 C (If thermostat starts opening between 85 0 C and 89 0 C and is fully open between 90 0 C and 100 0 C, it should be considered to be in a satisfactory condition.) 9 With thermostat still mounted on test stand connect water hose at outlet of thermostat (towards arrow head). 10 Connect inlet of thermostat to a hand operated water pump (water at room temperature). 11 Check flow of water at outlet under 1 bar pressure. It should be within specified limits. NOTE a. This flow is caused by a hole in valve head or corrugation on valve seat intentionally provided to ensure that cooling system can be completely filled with water when engine is cold. If this flow rate is too high, check visually for dirt particles which have settled down on the valve seat. b. If hole in valve head is clogged, it should be reopened by a sharp pointer.