Section 4.4 Coolant Pressure Control Cap

Section 4.4
Coolant Pressure Control Cap

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 99°C (210°F).‪

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 "Pressure Control Cap (Vacuum Valve Open)" . It also permits coolant to flow from coolant recovery bottle (when used) to the radiator tank.‪

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Figure 1. Pressure Control Cap (Vacuum Valve Open)

Section 4.4.1
Repair or Replacement of Pressure Control Cap

Refer to the OEM guideline for pressure control cap service procedure.‪

Section 4.4.2
Cleaning and Removal of Pressure Control Cap

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.‪

  1. Wipe the outside area on the pressure control cap clean before removal.
  2. Push down on pressure control cap while turning counter-clockwise.
Inspection of Pressure Control Cap

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.‪

Section 4.4.3
Installation of Pressure Control Cap

Install the pressure control cap as follows:‪

  1. Wipe area clean before installing the pressure control cap.
  2. Push down on pressure control cap while turning clockwise.

Series 50 Service Manual - 6SE50
Generated on 10-13-2008

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