The bypass hose allows coolant to reticulate within the locomotive, without fleeting through the radiator, as it does when the engine is warmed up and the thermostat opens. The bypass hose connects the thermostat accommodation and the water pump. The water enters the bypass tube through the bypass valve, when such a regulator is fitted. The bypass valve is sometimes operated thermostatically; it closes off the bypass hose when certain hotness is reached. This increases the flow of the coolant within the engine. Many cars don't need a bypass valve, as there is plenty of coolant leaving through the radiator hoses due to the thermostat.