Which is hotter, the upper or lower radiator hose under normal conditions?
2 Answers
When the thermostat is closed, the upper and lower hoses are at the same temperature. When the thermostat opens, the upper hose temperature is higher than the lower hose. Here are relevant explanations: 1. Thermostat working principle: The thermostat automatically adjusts the water flow entering the radiator based on coolant temperature, altering the water circulation range to regulate cooling capacity and ensure the engine operates within proper temperature ranges. The thermostat must maintain good technical condition, otherwise it will seriously affect normal engine operation. 2. Thermostat failure: A failed thermostat prevents water from being sent to the radiator even when reaching baseline temperature, or sends insufficient water, causing engine overheating and continuous operation of the electric fan.
Having driven for decades, I'm very familiar with the temperature changes in the radiator's upper and lower hoses. During normal operation, the upper hose is hot because it's directly connected to the engine outlet - the coolant coming from the engine is at high temperature, around 70-80°C, feeling scalding to touch. The lower hose is cool as the coolant returns to the engine bottom after being cooled by the radiator, at about 30-40°C, feeling warm. This temperature difference indicates proper cooling system function with smooth coolant flow. If the upper hose isn't hot or the lower hose becomes overheated, it might indicate fan failure, water pump malfunction, or a stuck thermostat, potentially causing abnormal temperature rise that could damage the engine. I always carefully touch the hoses with the back of my hand (never the palm to avoid burns) while driving, and immediately check if any abnormality is detected. For long-term maintenance, regularly cleaning debris from the radiator can prevent clogging and extend vehicle lifespan.
