coolant boils out the overflow. on 1996 Infiniti I30

When it is warm aoutside or I drive the car more than 150 miles the coolant level in the radiator gets low. I noticed it boils out the overflow. I had the thermostat replaced already. What else could the problem be?

Asked by for the 1996 Infiniti I30
What you see 'boiling' is probably combustion gasses leaking into the cooling system. That would explain the coolant loss, too. get the head gaskets checked for leaks by an Infiniti specialist.
If you want to find a specialist, here's a directory link for you: