Couple observations..
-The gauges on ZR-1/C4 are notoriously inaccurate
-Coolant temps should be in 190-205 F range
-LT-5 cooling has always been an issue... partly due to the radiator design & placement. Being a bottom feeder (for air flow over the radiator) all sorts of debris (big like leaves) and small (like dirt/grit/sand etc) which can (1) block air flow over the radiator and (2) actually clog the radiator itself (grit build up in the cooling veins of the radiator). Big stuff you can see collected on the front of the radiator, but the small stuff is not readily seen until the radiator shroud is removed.
-OEM program has fans coming on in a progressive fashion and there are aftermarket chips (Haibeck comes to mind
) that reprograms the fans to have both come on and come on at a lower temp than the factory setup.
How many miles on your ZR? Has the radiator core ever been inspected?