While they might have worn a Detroit badge, none of the Neon's predecessors were truly American. Most were Mitsubishis at heart: some, like the Dodge and Plymouth Colt and the Eagle Summit, were pure captive imports; the K-Car-based Sundance and Duster used Mitsubishi engines, and the Eagle Talon and Plymouth Laser were produced in conjunction with Mitsubishi. The Dodge Omni and Plymouth Horizon seemed American, but were in fact engineered by the French and used mutant Volkswagen engines in some markets. Love sporty compacts or hate them, but the Neon was at least as American as apple pie.
Park the car on level ground, set its parking brake and allow it to cool completely. Lift the front of the car with a floor jack and set it on jack stands. Open the coolant fill cap. Slide a coolant drain pan under the radiator and locate the coolant drain petcock valve; turn the valve counterclockwise and pull it toward the back of the car to open it.
Wait for the coolant to drain below the level of the thermostat housing, when you can no longer see coolant through the fill cap. Trace the tube from the coolant overflow tank to the fitting on the coolant fill cap neck and disconnect it. Use a pair of pliers to release the hose clamp that holds the upper radiator hose to the thermostat housing and slide the clamp down the hose.
Carefully wiggle the hose off of the thermostat housing. Use a ratchet and socket to remove the two bolts holding the thermostat housing to the engine, and pull the housing off to expose the thermostat. Pull the thermostat out of the engine, noting its orientation. Wipe the mating surface on the engine down with a clean rag.
Roll the sealing O-ring off of the old thermostat, and install it on the new thermostat with the small tab aligned with the vent vole in the thermostat. Alternately, you might consider installing a new O-ring on the new thermostat -- the old one gets hard over time and might not evenly conform to the new thermostat valve or fit inside the thermostat housing.
Install the new thermostat and O-ring assembly into the recess in the thermostat housing, ensuring that it matches the orientation of the thermostat as you pulled it out of the block. Install the thermostat housing onto the engine, and tighten the bolts to 9 foot-pounds with a torque wrench. Slide the upper radiator hose onto the thermostat housing and slide the clamp back up.
Reconnect the overflow tank hose. Refill the cooling system with the recommended mix of coolant and distilled water. Reinstall the coolant cap and tighten it down. Start the engine and allow it to idle up to temperature, until the thermostat opens and the cooling fans come on. Frequently check around the thermostat housing for leaks. Add coolant as necessary.
