Engine Cooling problem
1998 Cadillac SLS V8 All Wheel Drive Automatic 90,000 miles
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Good morning!

My car was driving well yesterday (hot day) and once I put it in reverse to back into a parking space I heard a sound (plaaaa) like something blew off. Then I noticed that my antifreeze was leaking on the ground, so I filled it with water to see if I could see where the leakage may be coming from; but there was steam coming upward and water still dripped slowly. (I saw steam while the hood was down; so I decided to park it until I am able to find out what the problem is and what to do next. Can you please help me with this question?

Thank you graciously for your time and consideration.