Why is the upper radiator hose hot while the lower one is not?
2 Answers
Car upper radiator hose being hot while the lower one is not is because the coolant is in a small circulation state. Here is an introduction to car engine hose knowledge: 1. Hose classification: Hoses are divided into upper hoses, lower hoses, and auxiliary tank connecting hoses. When a car is running, it generates heat, so water is used for cooling. 2. Function: There are many interconnected small passages in the engine block. The radiator's role is to store reserve water. When the water in the engine block reaches a certain temperature, the thermostat automatically opens. The water pump will then circulate the reserve water into the engine block. At this time, the upper hose is needed to transport the reserve water to the engine block, and the engine block then sends it back to the radiator through the lower hose. The hoses are like the roads that transport a car from one place to another.
I find it quite common that having a hot upper hose and a cool lower hose in a car is actually a good thing. After driving for a while, you'll understand it's a sign of the cooling system functioning properly. Hot coolant flows out of the engine, enters the top of the radiator through the upper hose, where the fan or natural airflow helps it cool down quickly, then exits through the lower hose and returns to the engine. This naturally creates a temperature difference: the upper part is the inlet for hot coolant, so it's hot; the lower part is the outlet for cooled coolant, so it's not hot. If both hoses are hot or both are cool, then there's a problem, such as a clogged radiator or a faulty water pump, causing the engine temperature to spike instantly, potentially damaging major components. I always make it a habit to feel the hoses and compare their temperatures before driving, then check the coolant level to ensure it's within the normal range. Regular maintenance, like flushing the radiator every six months, can prevent many issues—otherwise, a summer highway breakdown would be disastrous. These small details may seem simple, but they can help detect potential problems early.
