Pressure test the low-voltage cooling system on a 2024 Model 3 Performance to identify leaks in the powertrain/battery coolant loops without disturbing HV components. This is a diagnostic procedure performed at the coolant reservoir cap only.

Warnings

Tools required

Parts

• Coolant reservoir cap (replace if seal is damaged) × 1 — OEM Tesla coolant reservoir cap — refer to VIN

Fluids

• Tesla-spec coolant (G-48 compatible) — for top-off only if needed — 0.5 qt

Preparation

1. Park on level ground, place in P, engage parking brake.
2. Exit ALL doors with the key fob away from the vehicle. Wait at least 2 minutes for HV systems to fully de-energize, even on this non-HV job.
3. Disconnect the 12V low-voltage battery. On 2024 Model 3 Performance the low-voltage battery is typically a lithium unit — refer to architecture notes for exact location (behind right rear seat back panel on most years; some 2024+ have lithium 12V under floor).
4. DO NOT touch, cut, or pierce ANY orange cable — these are high-voltage and lethal.
5. If at any point you encounter an orange cable, an HV component, or are unsure if a system is de-energized: STOP and consult a Tesla-certified technician.
6. Allow the vehicle to sit for at least 2 hours after driving so coolant temperature and pressure normalize.
7. Open the front trunk (frunk) and remove the frunk liner/storage bin to access the coolant reservoir area.
8. Remove the front cowl/service cover per the manufacturer-specified procedure to expose the coolant expansion reservoir cap.
9. Visually inspect the reservoir, visible hoses, and clamps for stains, residue, or weeping before pressurizing.

Procedure

1. 1

   Locate coolant expansion reservoir
   Identify the coolant expansion/degas reservoir in the front compartment. On Model 3 it is a translucent plastic bottle with a pressure cap, located near the front of the vehicle behind the frunk tub. Verify coolant level is at or near the COLD/MIN-MAX band before testing.
2. 2

   Inspect coolant condition
   Note coolant color and clarity. Tesla-spec G-48 compatible coolant should be clear blue/teal without rust, oil sheen, or particulate. Cloudy or contaminated coolant indicates a deeper issue and should be reported. Record findings — Tesla recommends coolant inspection at 4 years / 50,000 mi.
3. 3

   Remove reservoir cap slowly
   With the system fully cooled, slowly rotate the cap to its first detent to release any residual pressure, then fully remove. Inspect the cap's rubber seal for cracks, swelling, or deformation — a failed cap seal is a common cause of slow coolant loss and false leak indications.
   ⚠Even on a cool Tesla, the loop can hold residual pressure from thermal cycling. Release pressure in stages.
4. 4

   Install pressure tester adapter
   Select the universal cap adapter that matches the reservoir neck threads. Thread the adapter onto the reservoir hand-tight only — do not over-torque plastic threads. Confirm a flush seal against the reservoir neck.
   ⚠The reservoir is plastic. Cross-threading or over-tightening will crack the neck and create a much larger leak than the one you are diagnosing.
5. 5

   Connect pressure tester pump
   Attach the hand pump to the adapter quick-connect. Confirm the gauge reads zero. Verify all hose connections on the tester are secure before pressurizing.
6. 6

   Pressurize the system
   Slowly pump the system up to the pressure stamped on the OEM reservoir cap (do not exceed it). For Model 3, this is typically a low-pressure system — refer to the cap marking for the exact value. Stop pumping immediately once target pressure is reached.
   ⚠️Exceeding rated cap pressure can rupture internal seals in the HV battery pack thermal loop. If unsure of rated pressure, STOP.
7. 7

   Observe gauge for 15 minutes
   Watch the gauge for pressure drop. A stable reading over 15 minutes indicates no significant leak. A slow drop indicates a leak; a rapid drop indicates a major leak or open circuit. Note the time-to-drop for diagnostic reference.
8. 8

   Visually trace for leaks (accessible areas only)
   With the system pressurized, inspect all accessible coolant hoses, clamps, the reservoir body, the front radiator, and visible hose junctions in the frunk area for weeping or dripping. Use a flashlight and mirror as needed. A UV dye + black light can help locate slow leaks.
   ⚠️DO NOT trace coolant hoses into the HV battery pack, octovalve, superbottle area, or anywhere near orange HV cabling. Leaks in those areas are dealer-only repairs.
9. 9

   Document findings
   Record where the leak originates (if any), pressure drop rate, and whether the cap holds pressure independently. If the leak is internal (no visible external leak but pressure drops), this strongly suggests an HV pack or octovalve internal issue — refer to Tesla service.
10. 10

    Test the cap separately
    Using the cap test adapter on the pressure kit, pressurize the OEM cap to its rated value and confirm it holds. A failed cap is inexpensive and often the actual culprit. Replace if the cap fails to hold or the seal is degraded.
11. 11

    Release pressure and remove tester
    Use the tester's bleed valve to slowly release system pressure to zero before disconnecting any fittings. Remove the pump, then unthread the cap adapter from the reservoir.
    ⚠Never disconnect the adapter under pressure — coolant will spray and the adapter can be ejected.

Reassembly

1. Top off coolant with Tesla-spec G-48 compatible coolant only if level dropped during testing — do not overfill above the MAX line.
2. Reinstall the OEM reservoir cap (or new cap if the original failed) and rotate to the fully locked position.
3. Reinstall the front cowl/service cover and frunk liner, ensuring all clips and fasteners seat fully. Torque any bracket fasteners to OEM specification — refer to Tesla Service Manual.
4. Reconnect the 12V low-voltage battery negative terminal last. Torque to OEM specification — refer to Tesla Service Manual.
5. Close the frunk and verify it latches normally.

Verification

• Power up the vehicle and check the touchscreen for any coolant temperature, battery thermal, or 'Service Required' alerts.
• Allow the vehicle to sit powered on for several minutes; the thermal management system will cycle pumps and the octovalve. Listen for unusual gurgling (indicates trapped air) and watch for new alerts.
• Drive the vehicle briefly (or run a Supercharge / DC fast preconditioning cycle if safe) to bring the loop up to operating pressure, then re-inspect the reservoir level after cooldown.
• Re-check coolant level after 24 hours of normal use — a drop indicates the leak was not fully identified.
• Note in service records: Tesla recommends battery coolant inspection at 4 years / 50,000 miles. If this test was performed as part of that interval, schedule the next inspection accordingly.

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