High Coolant Temperature Switch
This is a protective element that changes state when the coolant temperature exceeds a set threshold. Common standard threshold values are 100, 135, 150 and 200 degrees Celsius, and these switches are typically made as the normally closed type. Overheating, together with loss of oil pressure, forms the basic protection pair for engines.
The threshold is chosen according to the design of the engine's cooling system; a threshold around 100 °C is suitable on a water-cooled diesel, while higher values are used for oil or exhaust line measurements. The switch being normally closed means that if a wire breaks the circuit stays open and is seen as a fault; this is a choice that fails to the safe side.
The causes of overheating are usually simple: low water level, a blocked radiator core, a faulty thermostat, a loose belt or contaminated coolant. In dusty environments such as drilling and agriculture, blockage in front of the radiator is the most frequently encountered cause.
What must be known from the speed control point of view is this: lowering engine speed may ease the overheating but does not solve the fault, and moreover lowering the speed also lowers the fan speed and can make the situation worse. In addition, a temperature input is not declared on the GS740 and GS740-3P; the protection must be built into the engine's own chain.
The context in which this term is used: Electronic speed and throttle control on a diesel engine