Your car's cooling system needs coolant to keep it from overheating. Although water can be added to the radiator for this purpose, it's preferable to add a mixture of coolant and water because plain water can boil before the proper coolant will boil, causing your engine to overheat [source: pontiac]. However if you're stuck and don't have any coolant, you might want to know how to how to put water in your car radiator. Here's how to do it:

  1. Pay attention to the icon on your car's dashboard that indicates if the engine is overheating or if you're car's low on coolant. If the light comes on and stays on, it means you're low on engine coolant [source: pontiac]. A car radiator cannot work if there isn't enough coolant inside the system. The coolant level should be the first check after an engine has overheated [source: 2carpros].
  2. Ensure that there's no steam coming from the engine. Turn off the car, open the hood and locate the radiator.
  3. Don't touch anything until the radiator and engine have cooled down, as you might get scalded from the hot liquids [source: pontiac].
  4. Locate the coolant recovery tank. If the coolant is boiling, don't do anything until it cools down. It's preferable to let the engine cool off overnight [source: 2carpros].
  5. Remove the radiator pressure cap once the engine and radiator have cooled down.
  6. Check coolant level. The coolant should be between the MAX and MIN marks on the coolant reservoir when the engine is cool [source: mazda]. If the coolant is low, top it off by adding clean, drinkable water to the coolant reservoir [source: pontiac].
  7. Change your coolant every 40,000 to 100,000 miles (64,400 to 160,000 kilometers). Fill your radiator with a mixture of 60 percent coolant and 40 percent water. This mix will provide the best corrosion protection, and protect against freezing [source: 2carpros].
  8. Fill the reservoir to about an inch (2.5 centimeters) of the top, so there aren't any air pockets [source: Bumbeck].