Cooling System Pressure Test

This procedure tests the cooling system for leaks and verifies the pressure cap functionality using a cooling system pressure tester.

Warnings

Tools required

Parts

• Radiator cap (if defective) × 1 — OEM or equivalent 16 PSI cap

Fluids

• HOAT coolant 50/50 — 1 qt

Preparation

1. Ensure the engine is completely cold to the touch before beginning work
2. Park the vehicle on level ground and engage the parking brake
3. Open the hood and secure it in the open position
4. Place drip pans under the radiator area to catch any coolant spillage
5. Visually inspect the cooling system for obvious leaks, damaged hoses, or wet spots before testing

Procedure

1. 1

   Access the radiator cap
   Locate the radiator cap on top of the radiator at the front of the vehicle. On the 5.9L Cummins, the radiator is positioned behind the charge air cooler (intercooler). Verify the engine is cold by touching the upper radiator hose.
2. 2

   Remove the radiator cap
   Slowly turn the radiator cap counterclockwise to the first stop and allow any residual pressure to release. Once pressure is fully released, press down and continue turning counterclockwise to remove the cap completely. Inspect the cap for damaged seals, cracks, or corrosion.
3. 3

   Check coolant level and condition
   Verify the coolant level in the coolant recovery/degas bottle is between the MIN and MAX marks (when cold). Add HOAT 50/50 coolant to the recovery bottle if necessary to bring level within range. Check coolant condition for contamination, oil presence, or incorrect color. The coolant should be the red/orange HOAT (Mopar/G-05 type) formulation.
4. 4

   Install pressure tester adapter
   Select the correct adapter from the pressure tester kit that fits the radiator neck on the 2007 Ram 3500. Install the adapter firmly onto the radiator filler neck, ensuring it seats completely and forms a proper seal. The adapter should thread or lock securely depending on type.
5. 5

   Attach the pressure tester
   Connect the cooling system pressure tester to the installed adapter. Ensure the connection is tight and secure. Verify the tester gauge reads zero before beginning the test.
6. 6

   Pressurize the cooling system
   Slowly pump the pressure tester to build pressure in the cooling system. Bring the system to the pressure rating stamped on the radiator cap (verify actual cap rating; commonly around 15-16 PSI on these trucks). Monitor the gauge closely and do not exceed the cap's rated pressure to avoid damaging components.
7. 7

   Observe initial pressure reading
   Once at 16 PSI, stop pumping and observe the gauge for 2 minutes without adding pressure. The system should hold pressure with minimal drop (no more than 2 PSI loss in 2 minutes). A rapid pressure drop indicates a leak.
8. 8

   Inspect for external leaks
   With the system pressurized, visually inspect all cooling system components including: radiator tanks and core, upper and lower radiator hoses, heater hoses at firewall connections, water pump weep hole (located at bottom of pump), thermostat housing, overflow tank and hoses, and all hose clamps. Check the ground under the vehicle for dripping coolant. Use a flashlight to inspect hard-to-see areas.
9. 9

   Check engine block and cylinder head
   Inspect the engine block sides, rear of engine, and cylinder head for coolant seepage. On the Cummins diesel, pay special attention to the water pump area, freeze plug locations along the block, and the head gasket sealing surface. Look for wet spots or coolant residue.
10. 10

    Test radiator cap function
    Release pressure from the system by opening the tester relief valve. Remove the pressure tester and adapter. Install the radiator cap onto the pressure tester adapter (if your tester has cap testing capability) or a dedicated cap tester. Pump pressure and verify the cap releases at 14-18 PSI (16 PSI nominal). The cap should hold pressure below this range and release cleanly at its rated pressure.
11. 11

    Document findings
    Record all test results including maximum pressure achieved, pressure loss over time, location of any leaks found, and radiator cap release pressure. Take photos of any leaking components for repair reference.
12. 12

    Remove test equipment and reinstall cap
    Ensure all pressure is released from the system. Remove the pressure tester and adapter from the radiator. Wipe the radiator neck clean with a rag. If the radiator cap passed testing, reinstall it by pressing down and turning clockwise until it locks. If the cap failed, install a new 16 PSI cap.

Reassembly

1. Verify the radiator cap is properly seated and locked in place
2. Check that no tools or rags were left in the engine compartment
3. Wipe up any spilled coolant from the radiator and surrounding components

Verification

• The cooling system should have held 16 PSI with less than 2 PSI loss over 2 minutes if no leaks are present
• The radiator cap should release pressure between 14-18 PSI when tested
• No visible coolant leaks should be present at any cooling system component
• The coolant level should remain at the top of the radiator after testing
• If leaks were found, they should be documented with specific location and severity for repair planning

Related trouble codes on this vehicle

Codes that commonly send this job to the bay — tap one for symptoms, causes, and diagnostic steps.

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