Mazda Repair: Miata Cooling System, crank pulley, coolant level

Question
My 1990 Miata was running very poorly.  The harmonic balancer was replaced along with both belts.  Driving the car home from the repair shop, the car overheated, a brand new problem.  I took the car back (it overheated again on the 2 mile trip) and was shown a leak at the top of the radiator.  The resavoir level never went down, the leak is noticeable, but not pushing out much coolant.  If the coolant level does not visibly drop, can that slow leak cause the car to overheat traveling on a flat level road for five miles on a 60 degree day?
Can the overheating be caused in some way from the crank pulley replacement?  Again, I don't understand how a small leak that does not dramatically drop the coolant level cause an immediate overheating problem.  Does the coolant stop circulating becuase of the presure loss with the leakage at the top of the radiator?  Do you have any ideas what should be tested next if you think the radiator is not the primary problem?

Answer
no that leak would not cause the engine to overheat like that it's something else, possibly a bad water pump or maybe the belts were put on incorrectly causing the water pump to not function right and your engine ends up overheating. if the pump wasn't working right the coolant wouldn't circulate in the first place so there wouldn't be any pressure loss due to the crack of the radiator. ive had my water pump belt snap on my 626 and my car was overheating and coolant was coming out of the radiator overfill because the coolant wasn't circulating and was just sitting in the radiator boiling hotter then what it normally should.