I just had my radiator replaced after a leak continued to get worse until the coolant was basically going straight through it. The day after I picked it up there is coolant all over the floor in the passenger side and I have a low coolant message. I topped it up and it doesn't seem to have dropped again since over the last 2 days.

Is it possible that my mechanic over filled it and it has burst out at the heater core? What else might have caused this if its not leaking anymore?

 

I think it is just a bad time and heater core is leaking. You would not have noticed it before since the radiator was leaking.

 

When you replace the heater core, put the carpet back and remove the pad below it to squeeze out / rinse out the coolant that leaked onto it.