What Causes Coolant to Boil While the Temperature Gauge Shows Normal?

[LaRyder]

Here are the reasons why coolant may boil while the temperature gauge shows normal: 1. The generator is not generating electricity, leading to poor heat dissipation. 2. Insufficient coolant level, which can easily cause the coolant to boil. 3. Geographical factors, such as being on a plateau, where overheating is more likely. Below are precautions for using coolant: 1. Try to use the same brand of coolant. Different brands use different metal corrosion inhibitors, so mixing them is not advisable. 2. Most coolants have a shelf life of two years. Ensure the product is within its validity period when adding. When replacing, drain the old coolant completely, clean the cooling system thoroughly, and then add new coolant. 3. Avoid diluting with water. Traditional inorganic coolants should not be mixed with water, as this can cause sedimentation and severely impair the coolant's function. Organic coolants can be diluted with water, but excessive dilution should be avoided. 4. For vehicles using coolant, never top up directly with tap water; use distilled or deionized water instead.

[JudeLee]

That day I was driving out for a countryside trip. Right after I parked, I heard gurgling sounds from under the hood - the coolant was bubbling and boiling, yet the dashboard temperature gauge still showed the middle position. After consulting a mechanic friend, I learned this situation was most likely caused by a faulty radiator cap seal. A normal cooling system requires sufficient pressure to raise the coolant's boiling point - a worn-out leaking cap can cause the boiling point to drop below 100°C. Another possibility is degraded coolant that's lost effectiveness from prolonged use - insufficient concentration can also cause premature boiling. After replacing both the radiator cap and coolant, the problem was solved. I'd suggest not opening the hood immediately after stopping - wait for the temperature to drop before checking if the coolant has deteriorated.

[EmilianoAnn]

I remember last year my car had the same issue - coolant gushing out when climbing hills while the temperature gauge remained completely still. Later diagnostics revealed a faulty coolant temperature sensor stuck at a fixed position, perpetually displaying normal readings. Another possibility is a thermostat stuck in the closed position, causing localized overheating. Although the main circuit temperature appears normal, coolant around the cylinders can boil directly. If the water pump impeller is damaged or the radiator is clogged, coolant flow becomes restricted and vaporizes instantly at stagnant spots. Now I inspect the cooling system monthly, especially those rubber hoses - they must be replaced promptly when aged.

[OmarMarie]

The coolant is boiling but the temperature gauge shows normal, indicating a discrepancy between the instrument's detection point and the actual high-temperature area. There are two common causes: the coolant temperature sensor is poorly positioned and cannot monitor the engine's hot spot temperature, or a partial blockage in the cooling system leads to uneven temperature distribution. Last time, my car's radiator was clogged with scale in the upper half. Although the temperature at the lower hose where the sensor is located was normal, the coolant in the upper part of the engine was boiling. It is recommended to regularly flush the radiator with a specialized cleaner, and pay special attention to whether the water pump is making abnormal noises.

[DiBrody]

I've encountered this issue twice. The first time was due to too much water mixed in the coolant lowering the boiling point - I later learned to follow the manual's mixing ratio. The second instance was more troublesome: a slight crack in the cylinder head gasket allowed high-temperature gases from the combustion chamber to enter the cooling system, directly heating the coolant. These hidden faults are the hardest to diagnose - you need to test whether the cooling system pressure drops abnormally. Here's a lesser-known fact: when the cooling fan relay fails, insufficient heat dissipation during low-speed driving can also cause overheating. It's best to keep an OBD scanner handy to monitor coolant temperature data in real time.