I can think of Three things,
1. Thremostat stuck open.
2. Poor quality radiator hose or the spring inside is bent or missing.
3. Low water level in radiator.
Good Luck
Follow the upper rad hose from the rad to the engine.
Follow the upper rad hose from the rad to engine and it is in a housing on the engine.
at the emd of upper rad hose between outlet and block
At the engine end of the upper rad hose.
Follow the upper rad hose from the rad back to the engine. The part the Hose connects to on the engine is the thermostat housing. Remove it and the thermostat will be in there.
Follow the upper rad hose from the rad to the engine and at the engine there is a thermostat housing. When replacing the thermostat, make sure the spring goes toward the engine. The thermostat is located under the rad. cap from the top rad hose..
Follow the upper raditor hose from the raditor to the top of the engine.Where the upper rad hose ends on the engine is where the thermostat is.
where the upper rad hose meets the engine
Usually on the engine side of the upper rad hose in a housing
follow the upper rad hose from the radiator to the engine, it should be in the part that the upper hose connects to and bolted to the engine (if memory serves), this based on a g2500 with a 5.7
Under the upper rad hose. there should be a housing that's holding it
It is under the housing that the upper rad hose hooks to.