66 289 motor.... does the "spring" or the "button" face the engine when you install the thermostat?

 

Install with most of the thermostat below the housing......

Spring down...

 

So with a thermostat housing that is mounted on the front of the manifold, the spring would be on the motor side, and the Button on the radiator side...?

 

Sorry,,,, I was in "Chevy Land" for a moment,,, the big part of the thermostat (spring side) goes toward the back of the car.

"Small side" toward the front.

 

the spring side regulates how far this thing is open or closed.
if the water in engine is too cold, then the thing should stay closed, so the engine can heat up the water
if the water in engine is too hot, then the thing will slowly open, so you can mix the hot engien water with a bit of colder water from radiator. The hotter the engine, the wider it'll open to allow more water flow to rad.
So that's why the spring side has to be on engine side as JMD describes it