Why the he'll does dodge put 2 of these things in the car.

 

I guess in case one fails (open), the other will still close and the engine will heat up. Never knew that until I read the service manual. They open at different temps.

From the manual:



The primary thermostat is located on the front of the
water plenum in the thermostat housing/coolant inlet.
The thermostat has an air bleed vent located on its
flange. The air bleed vent (1) and the locator dimple
on thermostat seal provide for proper positioning of
thermostat in inlet housing.
The secondary thermostat is located in the cylinder
head under the water plenum.
OPERATION
The engine cooling thermostat is a wax pellet driven, reverse poppet choke type. The thermostat is designed to
provide the fastest warm up possible by preventing leakage through it and to guarantee a minimum engine operating
temperature of 88 to 93°C (192 to 199°F).
The primary thermostat starts to open at 77° C (171° F) and is fully open at 89° C (193° F). The secondary thermostat
starts to open at 95° C (203°F) and is fully open at 108° C (226° F).
The thermostat is operated by a wax filled chamber (pellet) which is sealed. When coolant reaches a predetermined
temperature, the wax expands enough to overcome the closing spring and water pump pressure, which forces the
thermostat to open. Coolant leakage into the wax pellet will cause a thermostat to fail in the open position. Do not
attempt to free-up a stuck open thermostat.
If the thermostat is stuck open or allows coolant leakage through it, the engine will not operate at the proper temperature
for obtaining engine fuel efficiency, performance and emissions levels. If this condition occurs, a diagnostic
trouble code will be set and a MIL light will be turned on. Refer to the Powertrain Diagnostic Procedures manual for
further information and diagnostics provided.
DIAGNOSIS AND TESTING - ENGINE COOLANT THERMOSTAT
The thermostat is operated by a wax filled chamber (pellet) which is sealed. When heated coolant reaches a predetermined
temperature the wax pellet expands enough to overcome the closing spring and water pump pressure,
which forces the valve to open. Coolant leakage into the pellet will cause a thermostat to fail open. Do not attempt
to free up a thermostat with a screwdriver.
Thermostat diagnostics is included in powertrain control module’s (PCM) programing for on-board diagnosis. The
malfunction indicator light (MIL) will illuminate and a diagnostic trouble code (DTC) will be set when an “open too
soon” condition occurs. Do not change a thermostat for lack of heater performance or temperature gauge position,
unless a DTC is present. For other probable causes, (Refer to 7 - COOLING/ENGINE - DIAGNOSIS AND TESTING).
Thermostat failing shut is the normal long term mode of failure, and normally, only on high mileage vehicles.
The temperature gauge will indicate this (Refer to 7 - COOLING/ENGINE - DIAGNOSIS AND TESTING).