White smoke (steam)?
Take off your oil fill cap and look at the underside. Whitish gooey gunk?
Pull the dipstick? Foam? More whitish gooey gunk?
Oil level up or down unexpectedly?
Water level up or down unexpectedly?
All these symptoms usually mean head gasket, cracked head, cracked block (the latter two are much less common).
If you car exhibits any of these symptoms, be sure to get it looked at right away. Water is not a good lubricant and oil is not a good coolant.
You can always live in your car, but you can't race your house...