What causes the slow rise in water temperature?
3 Answers
Water temperature rises slowly due to a damaged thermostat causing the coolant to continuously circulate in the large loop. The speed at which the water temperature rises is determined by the water temperature sensor's perception of the water temperature level. The functions of the water temperature sensor are: 1. Convert the coolant temperature into an electrical signal and input it into the ECU system; 2. Adjust the fuel injection quantity; 3. Adjust the ignition timing advance angle, increasing the ignition advance angle at low temperatures and preventing detonation and ignition delay at high temperatures; 4. Influence the idle control valve, where the ECU controls the idle control valve's operation and increases the idle speed based on the water temperature sensor signal at low temperatures; 5. Affect the EGR valve.
I remember a few years ago my car's water temperature always rose very slowly, especially in winter. It took a long time of driving before any warm air came out. Later, I figured it might be related to the thermostat, which controls the coolant circulation. If it's stuck in the open position, the engine keeps getting cooled and can't warm up properly. Insufficient coolant is also a common reason—leaks or too little coolant slow down heat transfer. Another issue could be a malfunctioning water pump, preventing proper circulation. These situations can cause faster engine wear, not to mention increased fuel consumption, and make driving in cold weather even more uncomfortable. So, it's recommended to regularly check the coolant level and look for any signs of leaks. When seasons change, take the car to a mechanic to inspect the thermostat and water pump. Don't wait until a major problem occurs to regret it.
Last time I was driving, the engine temperature took forever to rise, and the heater was blowing cold air. After checking, I found it was a thermostat failure—it's supposed to stay closed in cold weather to help the engine warm up faster, but since it was broken, it stayed open, circulating coolant continuously. Old coolant could also be the culprit; as water evaporates over time, the concentration increases, reducing heat transfer efficiency. Worn water pump impeller blades or loose bearings can decrease pumping power, preventing proper coolant circulation. All these issues affect driving comfort, forcing you to bundle up in freezing weather. I make it a habit to change the coolant regularly—every two years—and routinely check that the fluid level stays between the marked lines. If your engine consistently warms up too slowly, don’t delay—get it inspected by a professional shop to avoid excessive engine wear.
