It depends on "where" the crack is.
If you fill the bowl slowly, and the level goes down, that's not good.
If you have a second toilet, sometimes a flush that will force water out of a bowl when it's next door.
Just replaced upstairs toilet. It loses water in the bowl gradually gets to a certain level each time, doesnt completely drain. From reading previous posts sounds like a crack in the bowl.
It's the 1st time I've installed a toilet & was real concerned about getting the wax ring set right.
Another thing that happens. Once I've flushed it & the bowl fills I take a plunger & put it into the water & it basically has no suction & just pushes the water level down.
Normally if there's a crack does this leak into the actual pipe or is this damaging the floor? It's an upstairs toilet, so far ceiling is not wet on 1st floor & floor in bathroom is dry.