[Jake Raby]

Inspect the old pump for missing impeller blade pieces.. If it has any you MUST flush the entire cooling system until they are found, else a cracked head is in your future.

The engine could have overheated, it had to be hot for steam to be emitted from the overflow..

The coolant temp sensor is located centrally on the engine, if the pump takes a crap and the coolant isn't being circulated due to that, the sensor will never sample the hot coolant. Meanwhile the coolant in the heads is boiling hot!

Just because the gauge didn't show you a temp elevation doesn't mean the temperatures in the heads and cylinder didn't elevate. I'd go ahead and do a leakdown and compression test to ensure the cylinders didn't lose their integrity, just to be safe.