The radiator has a pressure control cap with a normally closed valve. The cap permits a pressure in the cooling system equal to the rating stamped on the top of the cap. A cap with a 9 stamped on top permits a cooling a system pressure of 62 kPa (9 lb/in.2 ) before the valve opens. See Figure 20521 . The maximum allowable coolant temperature, regardless of the pressure cap used, is 99 C (210 F).
Pressure Control Cap (Pressure Valve Open)
To prevent the collapse of hoses and other parts without internal support, a vacuum valve in the cap opens when the system cools. See Figure 20522 . It also permits coolant to flow from the coolant recovery bottle to the radiator tank.
Pressure Control Cap (Vacuum Valve Open)
Refer to OEM guidelines for pressure control cap service procedure.
Remove the pressure control cap as follows:
To avoid injury from the expulsion of hot coolant, never remove the cooling system pressure cap while the engine is at operating temperature. Remove the cap slowly to relieve pressure. Wear adequate protective clothing (face shield or safety goggles, rubber gloves, apron, and boots).
Clean and inspect the cap periodically. Check operation of both valves using test kit J 24460-01, or equivalent. Replace them, if necessary.
Detroit Diesel recommends that all on-highway vehicle engines use a minimum 62 kPa (9 lb/in.2 ) pressure control cap. If the pressure valve does not open between 55 kPa (8 lb/in.2 ) and 69 kPa (10 lb/in.2 ) or the vacuum valve does not open at 43 kPa (6.25 lb/in.2 ) (negative pressure), replace the pressure control cap.
Refer to OEM instructions for installation procedures.