Grand Cherokee 4WD Laredo V8-4.7L (2002)
Thermostat: Description and Operation
ENGINE COOLANT THERMOSTAT
DESCRIPTION-4.7L ENGINE
CAUTION: Do not operate an engine without a thermostat, except for servicing or testing.
A pellet-type thermostat controls the operating temperature of the engine by controlling the amount of coolant flow to the radiator. On all engines the
thermostat is closed below 195°F (90°C). Above this temperature, coolant is allowed to flow to the radiator. This provides quick engine warm up and
overall temperature control. On the 4.7L engine the thermostat is designed to block the flow of the coolant bypass journal by 50% instead of
completely blocking the flow. This design controls coolant temperature more accurately.
The same thermostat is used for winter and summer seasons. An engine should not be operated without a thermostat, except for servicing or testing.
Operating without a thermostat causes other problems. These are: longer engine warm up time, unreliable warm up performance, increased exhaust
emissions and crankcase condensation. This condensation can result in sludge formation.
OPERATION
The wax pellet is located in a sealed container at the spring end of the thermostat. When heated, the pellet expands, overcoming closing spring tension
and water pump pressure to force the valve to open.
