Replace it if necessary.

Inner Tube Inspection
Spring Tension InspectionWiring Diagram (Other than US, CA and CAL with KIBS Models)
ZX1000KC
ZX1000KD
...
Front Forks/Rear Shock Absorber Operation Inspection
Pump the forks down and up [A] 4 or 5 times, and inspect
the smooth stroke.
If the forks do not smoothly or noise is found, inspect the
fork oil level or fork clamps (see Front Fork Oil Change in
the Suspension chapter).
Pump the rear seat down and up [A] 4 or 5 times, and
inspec ...
Thermostat Inspection
Remove the thermostat (see Thermostat Removal).
Inspect the thermostat valve [A] at room temperature.
If the valve is open, replace the thermostat with a new
one.
To check valve opening temperature, suspend the thermostat
[A] in a container of water and raise the temperature
of ...