Cooling System Pressure Test

Perform a pressure test on the cooling system to diagnose leaks, verify cap integrity, and confirm system holds proper pressure.

Warnings

Tools required

Parts

• Coolant (if system requires topping off) × 1 — Use OEM specification

Fluids

• Zerex G-05 HOAT 50/50

Preparation

1. Ensure engine is completely cold to the touch (below 100°F). Verify this by feeling the upper radiator hose.
2. Park vehicle on level ground and engage parking brake.
3. Open hood and visually inspect cooling system components for obvious damage, corrosion, or previous leak evidence before testing.
4. Place shop towels or drain pan under radiator cap area to catch any minor coolant spillage during cap removal.

Procedure

1. 1

   Remove radiator cap and inspect
   Slowly turn the radiator cap counterclockwise to the first detent (pressure release position) and allow any residual pressure to escape completely. Once pressure is relieved, press down and continue turning counterclockwise to fully remove the cap. Inspect the cap gasket for cracks, hardening, or deformation. Check the pressure relief spring for corrosion or weakness. Verify the cap pressure rating embossed on the cap top and confirm it matches the OEM specification for this vehicle before testing to that value.
2. 2

   Check coolant level and condition
   Verify coolant is at the proper cold-fill level in the pressurized coolant expansion/reservoir tank (system should be full when cold). If low, add coolant meeting the OEM specification to bring to proper level before testing. Inspect coolant color and clarity; it should match the expected OEM coolant color and be relatively clear. Cloudy, rusty, or contaminated coolant indicates separate maintenance issues that should be addressed. Use hydrometer or refractometer to verify proper freeze protection if available.
3. 3

   Install pressure tester adapter
   Select the correct adapter from the pressure tester kit that matches the 2005 Viper pressure cap/filler neck (located on the coolant expansion tank) diameter and profile. Install the adapter by aligning it with the filler neck and turning clockwise or securing per the adapter design until it seats firmly and creates a seal. Install the adapter by aligning it with the radiator neck and turning clockwise or securing per the adapter design until it seats firmly and creates a seal. Ensure the adapter is fully engaged and not cross-threaded.
4. 4

   Attach pressure tester
   Connect the pressure tester pump to the installed adapter, ensuring all connections are tight and leak-free. Verify the pressure gauge reads zero before beginning to pump. If gauge shows residual pressure, bleed the tester according to manufacturer instructions.
5. 5

   Pressurize the cooling system
   Slowly pump the pressure tester to build pressure in the cooling system. Monitor the gauge continuously and stop pumping when pressure reaches the rating stamped on the OEM pressure cap. Do not exceed the cap rating by more than 2 PSI. The system should pressurize smoothly without excessive resistance or sudden pressure drops during pumping.
6. 6

   Observe initial pressure hold
   Once at 16 PSI, stop pumping and observe the pressure gauge for 30 seconds without touching the system. A healthy system will hold steady pressure or drop only 1-2 PSI maximum during this initial observation period. A rapid pressure drop (more than 3 PSI in 30 seconds) indicates a significant leak that requires immediate investigation.
7. 7

   Inspect engine bay components under pressure
   With system holding 16 PSI, systematically inspect all visible cooling system components in the engine bay. Check both radiator end tanks and core for seepage or drips. Inspect all hose connections at radiator inlet/outlet, heater core connections (passenger side firewall), thermostat housing, water pump, and overflow tank connections. Look for wetness, drips, or coolant spray. Pay special attention to the water pump weep hole (small hole on underside of pump housing) which will leak if pump seal is failing. Check expansion tank cap and tank body for cracks.
8. 8

   Inspect underside components
   Move to a position where you can view the underside of the engine and radiator area. Use flashlight to inspect lower radiator hose, water pump lower area, engine block core plugs (freeze plugs), and any coolant crossover pipes or fittings. Look for drips forming on the lowest points of components. Check the oil pan area for evidence of coolant (indicates head gasket or intake manifold gasket failure on some engines).
9. 9

   Check heater core and interior
   With system still pressurized, check inside the vehicle for evidence of heater core leakage. Inspect the passenger side floor carpet for wetness or coolant smell. Feel the carpet under the dashboard on passenger side. Check for coolant odor from dashboard vents. A failing heater core will often only leak under pressure and may not show symptoms during normal operation.
10. 10

    Perform 10-minute pressure hold test
    Return to the pressure gauge and note the current pressure reading. Allow the system to sit undisturbed for 10 minutes while monitoring the gauge periodically. A properly sealed system should lose no more than 2 PSI over this 10-minute period. If pressure drops more than 2 PSI, a leak exists but may be small or internal. Pressure loss without visible external leakage can indicate internal leaks such as head gasket failure (coolant entering combustion chamber) or a crack in the block or cylinder head.
11. 11

    Release pressure and remove tester
    After completing all inspections and the hold test, slowly release pressure from the system using the pressure tester's release valve. Allow pressure to return to zero on the gauge. Disconnect the pressure tester from the adapter, then remove the adapter from the radiator neck by turning counterclockwise or releasing per adapter design. Wipe any residual coolant from the radiator filler neck area.
12. 12

    Reinstall radiator cap
    Inspect the radiator cap one final time to ensure the gasket is clean and properly seated in the cap. Align the cap with the radiator neck and press down while turning clockwise until it reaches the first detent. Continue pressing and turning until it locks into the fully seated position. The cap should lock firmly with no play or looseness.

Reassembly

1. If any coolant was lost during testing, top off the system with Zerex G-05 HOAT 50/50 coolant to the proper level.
2. If leaks were found and repairs are required, plan appropriate repair procedures based on the leak location(s) identified during testing.

Verification

• System should have held 16 PSI for 10 minutes with no more than 2 PSI loss.
• No visible coolant leaks, drips, or seepage from any cooling system component.
• Radiator cap is properly seated and locked in place.
• Coolant level is at proper full mark when cold.
• Document all findings including pressure hold results and any leak locations for maintenance records.

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