If your car suddenly starts to steam then you need to pull over right away and turn off your engine. This could be a coolant leak causing the steam. If you drive with no coolant in your engine then it can cause the engine to overheat which will cause damage to your engine and other components. When in an emergency you can add water to your radiator until you can fill it with coolant. You should not drive your car with only water in your cooling system as it will not cool your engine properly.
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