Radiator Cap: Testing and Inspection
COOLING SYSTEM PRESSURE CAP TESTINGFig. 33 Testing Cooling System Pressure Cap:
Dip the pressure cap in water. Clean any deposits off the vent valve or its seat and apply cap to end of the Pressure Cap Test Adaptor that is included with the Cooling System Tester 7700 (Fig. 33). Working the plunger, bring the pressure to 104 kPa (15 psi) on the gauge. If the pressure cap fails to hold pressure of at least 97 kPa (14 psi), replace the pressure cap.
CAUTION: The Cooling System Tester Tool is very sensitive to small air leaks that will not cause cooling system problems. A pressure cap that does not have a history of coolant loss should not be replaced just because it leaks slowly when tested with this tool. Add water to the tool. Turn tool upside down and recheck pressure cap to confirm that cap is bad.
If the pressure cap tests properly while positioned on Cooling System Tester (Fig. 33), but will not hold pressure or vacuum when positioned on the filler neck. Inspect the filler neck and cap top gasket for irregularities that may prevent the cap from sealing properly.
RADIATOR CAP TO FILLER NECK SEAL
Fig. 34 Radiator Pressure Cap Filler Neck:
The pressure cap upper gasket (seal) pressure relief can be checked by removing the overflow hose at the radiator filler neck nipple (Fig. 34). Attach the Radiator Pressure Tool to the filler neck nipple and pump air into the radiator. Pressure cap upper gasket should relieve at 69 - 124 kPa (10 - 18 psi) and hold pressure at 55 kPa (8 psi) minimum.
WARNING: The warning words do not open hot on the radiator pressure cap is a safety precaution. When hot, pressure builds up in cooling system. To prevent scalding or injury, the radiator cap should not be removed while the system is hot or under pressure.
There is no need to remove the radiator cap at any time except for the following purposes:
1. Check and adjust coolant freeze point.
2. Refill system with new coolant.
3. Conducting service procedures.
4. Checking for vacuum leaks.
WARNING: If vehicle has been run recently, wait 15 minutes before removing cap. Then place a shop towel over the cap and without pushing down rotate counterclockwise to the first stop. Allow fluids to escape through the overflow tube and when the system stops pushing coolant and steam into the CRS tank and pressure drops push down and 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.
INSPECTION
Fig. 35 Cooling System Pressure Cap:
Hold the cap in your hand, top side up (Fig. 35). The vent valve at the bottom of the cap should open. If the rubber gasket has swollen, preventing the valve from opening, replace the cap.
Hold the cleaned cap in your hand, upside down. If any light can be seen between vent valve and the rubber gasket, replace the cap. Do not use a replacement cap that has a spring to hold the vent shut.
A replacement cap must be of the type designed for coolant reserve systems. This design ensures coolant return to the radiator.