Dodge Durango

 Service Manual

Cooling System » Description and operation
Radiator pressure cap

DESCRIPTION

All radiators are equipped with a pressure cap.

This cap releases pressure at some point within a range of 124-to-145 kPa (18-to-21 psi). The pressure relief point (in pounds) is engraved on top of the cap The cooling system will operate at pressures slightly above atmospheric pressure. This results in a higher coolant boiling point allowing increased radiator cooling capacity. The cap contains a springloaded pressure relief valve. This valve opens when system pressure reaches the release range of 124-to- 145 kPa (18-to-21 psi).

A rubber gasket seals the radiator filler neck. This is done to maintain vacuum during coolant cool-down and to prevent leakage when system is under pressure.

Fig. 5 Thermostat Cross Section View 4.7L

1 - FROM HEATER

2 - FROM RADIATOR

3 - TO WATER PUMP

4 - ENGINE BYPASS

5 - THERMOSTAT

OPERATION

A vent valve in the center of the cap will remain shut as long as the cooling system is pressurized. As the coolant cools, it contracts and creates a vacuum in cooling system. This causes the vacuum valve to open and coolant in reserve/overflow tank to be drawn through connecting hose into radiator. If the vacuum valve is stuck shut, or overflow hose is kinked, radiator hoses will collapse on cool-down.

Fig. 6 Radiator Pressure Cap-Typical

1 - FILLER NECK SEAL

2 - VACUUM VENT VALVE

3 - PRESSURE RATING

4 - PRESSURE VALVE

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