The only fix is to replace the CTS which isn't all that hard to do and they are not all that expensive if I recall correctly. The CTS for a 2.2/2.5 is in the thermostat housing. Best to replace when engine is cool. You will lose some coolant when removing the old CTS and installing the CTS. You can check the connections - they may be corroded or dirty but my bet is on the CTS itself.