Is there a sensor tht controls cooling sys. I changed radiator and thermostat.

No cooling system sensor will control the engine not getting to operating temperature. The lower radiator hose would carry coolant after radiator cooling. If there is too much cooling going on - such as a fan operating when it shouldn't be -- perhaps the coolant could cool down too much. Check for an air pocket in the cooling system as well. Places to start. Hands on testings is really what is needed.