The spring should be towards the motor. A very few are not round and have to be in the correct position which is obvious. As long as the plate in the middle of the thermostat is round, it can be in any position.
Easiest way to find it is to set #1 piston at TDC, remove the distributor cap and see where the rotor is pointing. It should be pointing to position #1 in relation to the distributor cap.
The rotor inside the distributor should be pointing at the #1 spark plug.
Position your feet pointing downstream so that they hit anything before your head does.
At tdc compression it should be pointing at #1 on the distributor cap.
the rotor should be pointing towards the number one plug position on the distributor cap, and the engine should be on compression stroke. If its not the motor will be 180 degrees out
just follow the upper radiator hose to the engine, remove hose from engine,thermostat should now be visable, note position of thermostat up position and gasket nubs if (3800engine) TIP- use a digital camera to take pictures for reference
they should be pointing down in the water
A thermostat that is stuck in the closed position is a very common cause of overheating. A new thermostat should be installed every time the coolant is changed.
The spring goes into the engine block.
Easiest way to find it is to set #1 piston at TDC and remove the distributor cap to see where the rotor is pointing. It should be pointing to #1 cylinder position in relation to the distributor cap.
pointing away from you..
If the thermostat is broken in the closed position the engine would overheat rapidly. If it was broken in the open position the engine cooling system would not reach normal operating temperature and the heater would produce only warm air. Take the thermostat out and put it in a pan of water on the stove. When the water gets to around 200 deg F, the thermostat should open. If it doesn't it needs replaced. Observe carefully that you have not installed the thermostat upsidedown.