Thermostat: Service and Repair
ENGINE COOLANT THERMOSTATREMOVAL-3.9L/5.9L ENGINE
WARNING: DO NOT LOOSEN RADIATOR DRAINCOCK WITH SYSTEM HOT AND PRESSURIZED. SERIOUS BURNS FROM COOLANT CAN OCCUR.
Do not waste reusable coolant. If solution is clean, drain coolant into a clean container for reuse.
If thermostat is being replaced, be sure that replacement is specified thermostat for vehicle model and engine type.
Factory installed thermostat housings on 3.9L and 5.9L engines are installed on a gasket with an antistick coating. This will aid in gasket removal and clean-up.
1. Disconnect negative battery cable at battery.
2. Drain cooling system until coolant level is below thermostat.
3. Air Conditioned vehicles: Remove support bracket (generator mounting bracket-to-intake manifold) located near rear of generator.
NOTE: On air conditioning equipped vehicles, the generator must be partially removed.
4. Remove accessory drive belt.
5. Remove two generator mounting bolts. Do not remove any wiring at generator. If equipped with 4WD, unplug 4WD indicator lamp wiring harness (located near rear of generator).
6. Remove generator. Position generator to gain access for thermostat gasket removal.
WARNING: CONSTANT TENSION HOSE CLAMPS ARE USED ON MOST COOLING SYSTEM HOSES. WHEN REMOVING OR INSTALLING, USE ONLY TOOLS DESIGNED FOR SERVICING THIS TYPE OF CLAMP, SUCH AS SPECIAL CLAMP TOOL (NUMBER 6094). SNAP-ON CLAMP TOOL (NUMBER HPC-20) MAY BE USED FOR LARGER CLAMPS. ALWAYS WEAR SAFETY GLASSES WHEN SERVICING CONSTANT TENSION CLAMPS.
CAUTION: A number or letter is stamped into the tongue of constant tension clamps. If replacement is necessary, use only an original equipment clamp with matching number or letter.
7. Remove radiator upper hose clamp and upper hose at thermostat housing.
8. Position wiring harness (behind thermostat housing) to gain access to thermostat housing.
9. Remove thermostat housing mounting bolts, thermostat housing, gasket and thermostat. Discard old gasket.
INSTALLATION-3.9L/5.9L ENGINES
1. Clean mating areas of intake manifold and thermostat housing.
2. Install thermostat (spring side down) into recessed machined groove on intake manifold.
3. Position thermostat housing to intake manifold. Note the word FRONT stamped on housing. For adequate clearance, this must be placed towards front of vehicle. The housing is slightly angled forward after installation to intake manifold.
4. Install two housing-to-intake manifold bolts. Tighten bolts to 23 Nm (200 inch lbs.) torque.
5. Install radiator upper hose to thermostat housing.
CAUTION: When installing the serpentine accessory drive belt, the belt must be routed correctly. If not, engine may overheat due to water pump rotating in wrong direction. Refer to figure for correct 3.9L and 5.9L engine belt routing. The correct belt with correct length must be used.
6. Air Conditioned vehicles; Install generator. Tighten bolts to 41 Nm (30 ft. lbs.).
7. Install support bracket (generator mounting bracket-to-intake manifold). Tighten bolts to 54 Nm (40 ft. lbs.) torque.
8. Install accessory drive belt.
9. Fill cooling system.
10. Connect battery negative cable.
11. Start and warm the engine. Check for leaks.