Why does the car's water temperature rise so slowly?

[MacCaroline]

The slow rise in car water temperature is caused by a damaged thermostat or the cooling fan running constantly. The thermostat operates based on the engine's water temperature. If the thermostat malfunctions and the valve fails to close, the coolant will continuously circulate in the large loop, potentially causing the engine's water temperature to remain too low. The water temperature refers to the temperature of the antifreeze, which is a coolant with anti-freezing properties. It prevents the coolant from freezing and expanding in cold winter conditions, which could crack the radiator or damage the engine cylinder block or head. The method for replacing antifreeze is as follows: 1. Open the vehicle's engine hood, and you can see the coolant reservoir in the upper right corner; 2. Open the antifreeze drain plug under the radiator to drain the old antifreeze; 3. Add new antifreeze, tighten the cap, and the antifreeze replacement is complete.

[McAnderson]

After repairing cars for ten years, I've found that if the engine temperature rises slowly, there's an 80% chance the thermostat is stuck. This component acts like a valve, controlling whether the coolant takes the small or large circulation route. When stuck in the large circulation position, the coolant flows directly into the radiator for cooling after a cold start, preventing the engine temperature from rising properly. In some older cars, it can take up to five minutes for the temperature gauge to reach one-third, which is barely tolerable in summer but a real ordeal in winter when you need the heater. It's also worth checking if the coolant level is sufficient, as dirty coolant clogging the pipes can hinder warming up. The most troublesome issue is a slight leak in the cylinder head gasket allowing exhaust gases to enter the coolant system. If you notice emulsified engine oil along with this, it's a sign that a major overhaul is needed.

[StJoseph]

Last time I took my dad's old pickup truck on a long trip, I encountered this issue. After a cold start, even after driving for half an hour, the temperature gauge was still at the lowest mark, and the warm air blowing out was cold. The mechanic said there were two main reasons: first, the thermostat was stuck open, causing the coolant to continuously circulate through the radiator; second, the temperature sensor was inaccurate, sending false data to the computer. He also taught me a simple trick: feel the upper hose from the engine to the radiator—if it gets hot shortly after starting, it means the thermostat isn't closing. Later, I replaced it with an electronic thermostat, and now even at minus ten degrees Celsius, hot air comes out in just three minutes.

[GeorgeLee]

Most people are unaware that an over-engineered cooling system can also cause this issue. Some eco-friendly vehicles are equipped with high-power electric water pumps, where the computer forces the coolant into the main circulation immediately after a cold engine start to accelerate warm-up, but this often backfires. Using the wrong oil viscosity is also a common problem. For instance, vehicles in northern regions using 0W-20 oil warm up significantly faster than those using 5W-40. Modified cars require extra attention; owners who upgrade to larger radiators often complain about slow temperature rise, when in fact, an oversized radiator can actually hinder the warm-up speed.