Why does the water temperature rise slowly?
3 Answers
Slow rising of water temperature indicates a malfunctioning thermostat. The thermostat is installed on the water inlet pipe of the heat exchanger, serving to maintain a constant water temperature. It continuously monitors the coolant temperature in the engine, keeping the water temperature around 80 to 90 degrees Celsius to ensure the engine operates within the optimal temperature range. The solution for slow water temperature rise is to first check if there are issues with the cooling system, such as blocked louvers, deformed fan blades, or short circuits in the water temperature sensor and its circuit. The thermostat can be removed and inspected by placing it in water at different temperatures to observe its opening behavior. If it fails to open and close properly, the thermostat should be replaced.
I often encounter this issue when repairing cars. If the engine temperature rises slowly, it's most likely due to a faulty thermostat. That small valve is supposed to stay closed when the engine is cold, allowing the coolant to circulate only within the engine to help it warm up faster. However, if it gets stuck in the open position, the coolant keeps flowing to the radiator, causing heat loss. Insufficient or poor-quality coolant can also slow down the warming process due to low heat transfer efficiency. This is more noticeable in winter when the outside temperature is low, and the engine starts cold. Incomplete combustion in the engine itself could also be a cause. Driving habits, like short trips where the engine doesn't have time to warm up before shutting off, can contribute. I recommend checking the thermostat and coolant level first, and performing regular maintenance to avoid engine wear. Don't ignore this issue—over time, it can affect the car's performance and even increase fuel consumption. For safety, it's better to let the engine warm up for a few minutes before turning on the heater.
Having driven for over a decade, slow engine temperature rise is most common in winter. After parking overnight in freezing conditions, the entire engine starts ice-cold, naturally warming up slowly. Sometimes it's a thermostat issue, but more often it's caused by short trips—like driving just minutes to work before the engine fully warms up. Aged or overly diluted coolant with insufficient heat capacity can also be the culprit. From personal experience, changing to fresh coolant noticeably improved warm-up time. A simple check: pop the hood to inspect coolant clarity and level. Additionally, running cabin heat draws significant warmth—try turning it off temporarily. When coolant temperature is low, heating performance suffers, leaving the cabin uncomfortably chilly.
