steam from tailpipe

Is it overheating ?
Are you losing any coolant
check headgasket
is it running rough

not running rough, coolant is low, but cylinders are dry, just steam out of tailpipe

The cylinders will always be dry after running the engine. Pressure test the cooling system to see if it hold pressure. It could be an intake gasket on a V6 but could also be a blown head gasket, especially if it has any overheating history.

the owner said it never overheated before, just the steam.

Low coolant and steam out the back ,never overheated on them ???

Manifold is common but if its been overheating you have to consider headgasket
have to do your checks before you go and replace the manifolds and then to find out ,have to be removed again to do the headgasket

There may be no way to know for sure without pulling the manifold and examining the intake gasket. the bad spot would be visible on the gasket.