Can Tap Water Be Used as a Substitute for Car Coolant?

[OmarLee]

Coolant cannot be replaced with water. If water has been added, it is recommended to drive the car to the nearest repair shop to drain the coolant mixed with water. The reason is that coolant has functions such as anti-freezing and anti-corrosion, while the water added contains many impurities that can cause blockages in the water passages of the radiator. Car coolant should be replaced every year. Coolant protects the engine's cooling system from corrosion, effectively prevents the formation of dirt and overheating of the car radiator, provides long-term comprehensive protection, and reduces the impact of the cooling system on the car engine's performance. Coolants should not be mixed either. Mixing different brands of coolant can easily cause chemical reactions such as sedimentation and bubbles, thereby reducing the performance of the coolant. It may also damage rubber seals, or even cause leaks at the water pump seal and welding points. Even if the coolants are of the same color, it is advised not to attempt mixing them when uncertain.

[DelErin]

I once had the experience of adding tap water when the coolant was insufficient. It happened during a summer trip out of town when the engine suddenly overheated. In a panic, I added some tap water as an emergency measure. The result was that the water temperature still soared. Later, at the repair shop, rust and scale deposits were found inside the coolant pipes. The mechanic explained that specialized coolant not only cools but also contains anti-corrosion and anti-boiling additives, with a boiling point exceeding 120°C. Tap water contains minerals like calcium and magnesium, which can cause internal rust and clog the pipes. Long-term use may damage the water pump and radiator. Even worse, in winter, it may freeze and expand, damaging the engine. Since then, I've developed the habit of checking the coolant level every six months, keeping it between the min and max lines. A 50% coolant and distilled water mixture is ideal. In emergencies, tap water can be used temporarily, but it must be replaced with professional coolant as soon as possible to protect the vehicle. Safe driving relies on proper cooling system maintenance—don’t risk major damage for minor savings.

[SanAriel]

As a frequent driver, I highly value the role of coolant. It not only prevents freezing but also offers anti-corrosion and anti-boiling functions, ensuring the engine doesn't overheat or freeze. While tap water may seem convenient and cheap, I've learned from a friend's experience that using it as a substitute can accelerate scaling in the cooling system, accumulate rust in the pipes, and increase maintenance costs. For instance, after a short trip, the engine warning light came on, only to discover it was caused by overheating due to tap water. More critically, when driving at high speeds or during winter, boiling and freezing points are vital. Coolant is designed to handle extreme temperatures, whereas tap water boils at 100 degrees. I recommend regularly checking the coolant reservoir and topping it up with distilled water or a dedicated replenishment fluid instead of tap water if it's low. Although tap water can be used briefly in emergencies, don't skimp on this expense—professional coolant extends vehicle lifespan and prevents sudden breakdowns that could compromise safety.

[VonAthena]

I know many people want to save money by using tap water, but this is wrong. Coolant needs to prevent boiling and freezing. Tap water has a low boiling point which may cause engine overheating, and it contains impurities that can lead to corrosion. Maintaining the cooling system is quite simple—just mix coolant with water as instructed in the manual. Using pure tap water is not acceptable. I've seen cars damaged due to long-term use of tap water, ultimately costing more in repairs. Remember to check that the fluid level doesn't drop below the MIN line and replenish with the proper fluid promptly. Safety comes first.