The radiator (or expansion tank) has a pressure control cap with a normally closed valve. The cap is designed to permit a pressure in the cooling system equal to the rating stamped on the top of the cap. A cap with a "9" on the top allows the cooling system to develop 62 kPa (9 lb/in.2 ) before the valve opens. This system pressure raises the boiling point of the coolant and reduces coolant loss. The maximum allowable coolant temperature, regardless of the pressure cap used, is 99C (210F).
To prevent collapse of hoses and other parts which are not internally supported, a second valve in the cap opens under vacuum when the system cools. See Figure 20522 . It also permits coolant to flow from coolant recovery bottle (when used) to the radiator tank.
Pressure Control Cap (Vacuum Valve Open)
Refer to the OEM guideline for pressure control cap service procedure.
Remove the pressure control cap as follows:
To avoid scalding from the expulsion of hot coolant, never remove the cooling system pressure cap while the engine is at operating temperature. Wear adequate protective clothing (face shield, rubber gloves, apron, and boots). Remove the cap slowly to relieve pressure.
Detroit Diesel does not offer pressure control (radiator) caps as original equipment on Series 50 engines.
Clean and inspect cap periodically. Check operation of both valves using test kit J 24460-01 or equivalent. Replace if necessary. Inspect and clean fill neck. Replace if damaged.
It is recommended that all Series 50 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 4.3 kPa (0.625 lb/in.2 ) (differential pressure), replace the pressure control cap.
Install the pressure control cap as follows: