Here's some info from the 2008 factory service manual:
Thermostat diagnostics is included in Totally Integrated Power Module's (TIPM) programming 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 - 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.
GAS - PRIMARY THERMOSTAT
1. Partially drain cooling system (Refer to 7 - COOLING - STANDARD PROCEDURE).
2. Remove air filter housing.
3. Disconnect coolant hose (1) from inlet housing (2).
4. Remove inlet housing bolts (3).
5. Remove thermostat assembly, and clean sealing surfaces.
GAS - SECONDARY THERMOSTAT
1. Partially drain cooling system. (Refer to 7 - COOLING - STANDARD PROCEDURE).
2. Remove air filter housing .
3. Disconnect coolant hoses (1) from rear of coolant adapter (2).
4. Remove radiator hose (3).
5. Remove radiator hose (4) from front of coolant adapter (2).
6. Remove coolant adapter mounting bolts.
7. Carefully slide coolant adapter off water pump inlet tube and remove coolant adapter (2) and secondary thermostat.
08 Sport 4x4 FDI Silver, CRD Stu's Coil Springs
, Mud Flaps, Weathertech vent shades, TAG Rear Bumper
Carr Lightwing, Pilot Navigator Driving Lights, K&N Air Filter and a jp.com decal
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