Radiator Pressure Cap; Description; Operation - Chrysler 2005 Crossfire SRT6 Service Manual

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RADIATOR PRESSURE CAP

DESCRIPTION

The pressure cap is located on the coolant reservoir.
The pressure cap is made of high strength plastic, and
screws onto the coolant reservoir tank. The cap con-
tains a springloaded pressure relief valve, and a
spring loaded vacuum relief valve.

OPERATION

The pressure cap performs two tasks in a closed cooling system. The pressure cap must allow the cooling system
to build pressure during engine operation, and allow the cooling system to loose pressure when not operating.
With the engine operating, the pressure cap must allow the cooling system to operate at higher than atmospheric
pressure. This increased pressure raises the boiling point of the coolant, thereby allowing the cooling system to
operate more efficiently. However, under excessive pressure, 110 kPa ± 14 kPa (16 psi ± 2 psi) the cooling system
will overcome the spring pressure in the pressure cap and allow engine coolant to flow into the reservoir. This pres-
sure relief will continue until the pressure is reduced and the spring in the pressure cap can return to its normally
closed position.
With the engine not operating, the pressure cap must allow the cooling system to loose pressure and recover
engine coolant. This recovery is accomplished through the use of a lighter spring in the pressure cap. As the hot
engine coolant cools, it creates a vacuum in the cooling system. As this vacuum is created, it pulls the vacuum
valve open and allows engine coolant to be pulled back into the engine from the coolant reservoir tank. This con-
tinues until the system pressure is equalized, and the vacuum valve is then returned to its normally closed position.
CAUTION: Use only the pressure cap specified for this vehicle. Use of other pressure caps can lead to cool-
ant loss and overheating.
WARNING
WARNING: THE WARNING WORDS "DO NOT OPEN WHEN HOT" ON THE COOLANT RECOVERY RESER-
VOIR PRESSURE CAP IS A SAFETY PRECAUTION. WHEN HOT, PRESSURE BUILDS UP IN COOLING SYS-
TEM. TO PREVENT SCALDING OR INJURY, THE COOLANT RECOVERY RESERVOIR PRESSURE CAP
SHOULD NOT BE REMOVED WHILE THE SYSTEM IS HOT AND/OR UNDER PRESSURE.
There is no need to remove the pressure cap at any time except for the following purposes:
• Checking and adjusting the coolant freezing point.
• Refilling system with new coolant.
• Conducting service procedures.
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