What you need to do is follow the hose from the radiator and find where it goes into the engine. That is usually where it is located. It depends on your vehicle. A little more information about your vehicle: make, model, year, etc. would be helpful.
Spring side down, to the engine
The spring goes towards the engine.
Usually the side with the spring goes to the engine side.
The spring side goes into the engine.
A thermostat always goes in spring side toward the engine.
The spring side of any thermostat always goes towards the engine.
The side with the spring faces into the engine.
The side of the thermostat that has a spring showing faces into the engine.
the spring side goes into the engine
tee-pee side up, other side into the engine.
The spring goes to the engine side.
Spring side goes towards engine.