Originally Posted by MightyBobo

This isn't the end of the world...you could effectively drive a car with pure water in it, and windshield washer fluid isn't exactly soapy. In fact, antifreeze is likely added TO the fluid, to lower its freezing point to make it a de-icing fluid. Now, I'm not saying he should keep it in there, but don't lose your s-it here - the motor is going to be fine. Just get it flushed out and you'll be good to go.