can you put water in a car radiator

[GabrielaFitz]

You can use water in a car radiator only in an absolute emergency, such as being stranded with an overheating engine. However, it is a temporary fix to get you to a repair shop. For normal operation, a proper mixture of coolant and water is essential. Using plain water long-term can cause severe damage, including corrosion, freezing in winter, and boiling over in summer.

A 50/50 mix of antifreeze coolant and distilled water is the industry standard, recommended by every major automaker. Coolant, or antifreeze, contains corrosion inhibitors that protect the aluminum, iron, and copper components inside your engine's cooling system from rust and scale buildup. It also raises the boiling point and lowers the freezing point of the liquid far beyond what plain water can achieve.

The following table compares the properties of water versus a proper coolant mixture:

Property	Plain Water	50/50 Coolant/Water Mix
Freezing Point	32°F (0°C)	-34°F (-37°C)
Boiling Point	212°F (100°C)	265°F (129°C)
Corrosion Protection	None	Excellent
Lubrication for Water Pump	Poor	Good
Recommended Use	Emergency Only	Normal Operation

If you must add water in a pinch, use distilled water, which is mineral-free. Tap water contains minerals that can accelerate corrosion and deposit scale, clogging the narrow passages in your radiator and heater core. As soon as possible, have the system drained, flushed, and refilled with the correct coolant specified in your owner's manual. Driving with only water, especially in cold climates, risks cracking your engine block, a repair that can cost thousands of dollars.

[DeLawson]

Only if you're stuck on the side of the road and the engine is overheating. It's a "get-home" trick, not a solution. Water doesn't protect your engine from corrosion or extreme temperatures like proper coolant does. Get to a mechanic ASAP to have the system flushed and filled with the right 50/50 coolant mix. Using water long-term is asking for a huge repair bill.

[StJuliana]

Think of coolant as a multi-tool and water as just a simple wrench. Yes, water can transfer heat, but that's all it does. Coolant does that plus it fights rust, lubricates the water pump, and won't freeze solid in winter. I made the mistake of using water years ago and it ended up costing me a radiator. Always use the pre-mixed coolant from the auto parts store; it's foolproof.

[McLane]

As a temporary measure, yes, but understand the risks. Your cooling system is a complex network of metals—aluminum, steel, copper. Water actively promotes corrosion in this environment. The additives in coolant form a protective coating on all internal surfaces. Without it, you're slowly destroying the system from the inside out. If you add water, plan to do a complete coolant flush very soon to prevent expensive damage to the radiator and heater core.