Dodge Durango

 Service Manual

Cooling System » Description and operation
Thermostat-4.7L engine

DESCRIPTION

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 195F (90C). 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 (Fig. 5).

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 warmup time, unreliable warmup performance, increased exhaust emissions and crankcase condensation. This condensation can result in sludge formation.

Fig. 4 Thermostat-Typical

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.

Cooling system

Coolant reserve/overflow system

Thermostat-5.2L/5.9L engines

Thermostat-4.7L engine

Radiator pressure cap

Radiator

Water pump

Water pump bypass-4.7L

Water pump bypass hose-5.2L/5.9L engines

Automatic transmission oil coolers

Automatic belt tensioner

Block heater

Hose clamps

Viscous fan drive