Pressure Cap - Chrysler 300M Service Manual

LH
RADIATOR DRAINCOCK (Continued)
Fig. 19 DRAINCOCK
1 - DRAINCOCK ASSEMBLY
(2) Position the draincock assembly horizontally to
the tank opening with the manufactures identifica-
tion mark facing down.
(3) Push the draincock assembly into the tank
opening while rotating clockwise until it snaps into
place.
(4) Close the draincock stem by turning clockwise
until it stops at the horizontal position.
(5) Fill the cooling system (Refer to 7 - COOLING
- STANDARD PROCEDURE).

PRESSURE CAP

DESCRIPTION
The cooling system cap is located on the coolant
pressure bottle. The cap construction includes; stain-
less steel swivel top, rubber seals and retainer, main
spring, and a spring loaded valve (Fig. 20).
OPERATION
The pressure cap allows the cooling system to oper-
ate at higher than atmospheric pressure which raises
the coolant boiling point, thus allowing increased
radiator cooling capacity. The pressure cap releases
pressure at some point within a range of 110 kPa ±
14 kPa (16 psi ± 2 psi) (Fig. 20).
A spring-loaded vent valve in the center of the cap
allows the system to pressurize and depressurize
without creating a vacuum. If the valve is stuck
open, coolant will escape to the overflow hose. There
is also a gasket in the cap to seal to the top of the
filler neck.
CAUTION: Use only the pressure cap specified for
this vehicle. Use of other pressure caps can lead to
coolant loss and overheating.
Fig. 20 PRESSURE CAP
1 - MAIN SPRING
2 - GASKET RETAINER
3 - STAINLESS STEEL SWIVEL TOP
4 - RUBBER SEALS
5 - SPRING LOADED VALVE
6 - COOLANT PRESSURE BOTTLE
7 - FILLER NECK
8 - OVERFLOW NIPPLE
INSPECTION
WARNING: IF VEHICLE HAS BEEN RUN RECENTLY,
WAIT 15 MINUTES BEFORE REMOVING CAP. THEN
PLACE A SHOP TOWEL OVER THE CAP AND WITH-
OUT PUSHING DOWN ROTATE IT COUNTERCLOCK-
WISE TO THE FIRST STOP. ALLOW FLUIDS TO
ESCAPE THROUGH THE OVERFLOW TUBE AND
WHEN THE SYSTEM STOPS PUSHING OUT COOL-
ANT AND STEAM
REMOVE THE CAP COMPLETELY. SQUEEZING THE
RADIATOR INLET HOSE WITH A SHOP TOWEL (TO
CHECK PRESSURE) BEFORE AND AFTER TURNING
TO THE FIRST STOP IS RECOMMENDED.
WARNING: THE WARNING WORDS DO NOT OPEN
HOT ON THE COOLANT BOTTLE PRESSURE CAP
IS A SAFETY PRECAUTION. WHEN HOT, PRES-
SURE BUILDS UP IN COOLING SYSTEM. TO PRE-
VENT SCALDING OR INJURY, THE COOLANT
BOTTLE PRESSURE
REMOVED WHILE THE SYSTEM IS HOT AND/OR
UNDER PRESSURE.
The pressure cap upper gasket (seal) pressure
relief can be checked by removing cap. Attach a suit-
able Cooling System Tester such as Tool 7700 to the
cap and pump air into the cap. Pressure cap upper
gasket should relieve at 124 kPa (18 psi) and hold
pressure at 110 kPa (16 psi) minimum.
Remove the pressure tester and hold the cap in
hand, right side up (Fig. 21). The vent valve at the
bottom of the cap should not open. If the rubber gas-
ENGINE 7 - 29
AND PRESSURE DROPS,
CAP SHOULD NOT BE