What Causes the Upper Radiator Hose to Be Hot While the Lower Hose Remains Cool?

1 Answers
SophiaMarie
07/29/25 10:48pm
There are two main reasons for the upper hose being hot and the lower hose remaining cool: Thermostat: A malfunctioning thermostat that fails to open causes the cooling system to operate in a small circulation mode. Coolant Pump: If the coolant pump is not functioning, it prevents the coolant from circulating, leading to the described situation. Inspection Methods: Temperature Difference: If there is no high coolant temperature warning and the temperature difference is noticed while the vehicle is idling without moving, it is recommended to drive until the electric fan operates and then recheck for any temperature difference. Thermostat: Based on the described scenario, the thermostat is not opening, keeping the cooling system in small circulation mode. The electronic thermostat is controlled by the engine's computer based on engine temperature and load.
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