Pressure test the low-voltage cooling system on a 2024 Model S Plaid to identify leaks in the powertrain/battery coolant loops without disturbing HV components. This is a non-invasive diagnostic that pressurizes the coolant circuit through the expansion tank to check for drops over time.

Warnings

Tools required

Parts

• Replacement coolant expansion tank cap (if cap fails seal test) × 1 — Tesla-spec Model S coolant cap — verify by VIN

Fluids

• Tesla Battery/Motor Coolant (G-48 equivalent) — top-up only if level low — 0.5 qt

Preparation

1. TESLA SAFETY PREAMBLE: Park on level ground, place in P, engage the parking brake.
2. Exit ALL doors with the key fob carried at least 3 meters away from the vehicle. Wait at least 2 minutes for HV systems to fully de-energize, even on this non-HV job.
3. Open the frunk. Disconnect the low-voltage battery: on 2024 Model S Plaid this is the 16V lithium unit (verify location by VIN — frunk under the nose cowl on most builds, or under the rear seat on some Plaid configurations). Remove the negative terminal first using the manufacturer-specified procedure.
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 cool for a minimum of 2 hours after any driving so that the cooling system is at ambient temperature and not pressurized.
7. Identify the coolant expansion/degas bottle at the front of the vehicle (frunk area, behind the cowl). Note the cap pressure rating stamped on the cap.
8. Have absorbent pads ready under the bottle area to catch any minor coolant weep when the cap is removed.

Procedure

1. 1

   Inspect coolant level and condition
   With the system cold, visually verify the coolant level in the expansion tank is between MIN and MAX. Note color and clarity — Tesla-spec G-48 coolant should be pink/red and translucent. Cloudy, brown, or oily-looking coolant indicates a separate problem (possible heat exchanger fault) and should be investigated before pressure testing.
   ⚠If coolant is significantly low, find the leak before pressure testing — adding pressure to a system with a known external leak can spray hot coolant later if the test is repeated warm.
2. 2

   Remove the expansion tank cap
   Confirm the system is cold to the touch. Slowly rotate the expansion tank cap counter-clockwise to its first detent to release any residual pressure, then fully remove. Inspect the cap's rubber seal and spring — a hardened or cracked seal will fail the test even if the system itself is sound.
   ⚠️If you hear hissing or feel heat through the cap, STOP and let the system cool further.
3. 3

   Test the cap independently
   Install the expansion tank cap onto the pressure tester's cap adapter. Pump up to the cap's rated pressure. The cap should hold pressure for at least 30 seconds without dropping more than ~1 psi. If the cap fails, replace it with a Tesla-spec replacement and re-test before continuing.
4. 4

   Install pressure tester on expansion tank
   Select the correct adapter from the pressure tester kit that mates to the Model S expansion tank neck. Thread or lock the adapter onto the tank by hand only — do not use tools. Confirm a clean, square seal. Connect the pump and gauge assembly to the adapter.
   ⚠Cross-threading the adapter on the plastic tank neck will destroy the tank. Hand-thread carefully and stop immediately if you feel resistance.
5. 5

   Pressurize the system
   Slowly pump the tester up to the cap's rated pressure (do NOT exceed it). Watch the gauge while pumping — an immediate inability to build pressure indicates a large leak; stop pumping and locate it before continuing.
   ⚠Never exceed the cap's stamped rating. The degas bottle, hose clamps, and quick-connect fittings on Tesla coolant lines are designed for that ceiling only.
6. 6

   Hold and observe
   Allow the system to sit pressurized for 15 minutes. A healthy system should drop no more than ~2 psi in that time. Record the starting pressure and the pressure at 5, 10, and 15 minutes. A steady, slow drop typically indicates a small external leak; a rapid drop indicates a larger leak or internal failure.
7. 7

   Locate external leaks
   While the system is pressurized, inspect all visible cooling system points: expansion tank seams, upper and lower radiator hoses, radiator end tanks, front condenser/radiator stack, coolant pump housings, and any visible quick-connect fittings near the front of the vehicle. Use a flashlight and mirror. Wet spots, dried pink/red residue, or active drips indicate the leak point.
   ⚠️Do NOT trace coolant lines that route into the HV battery pack, the drive unit housings, or the Octovalve/superbottle assembly. If the leak appears to originate from any of those areas, STOP — this becomes an HV-adjacent repair requiring Tesla-certified service.
8. 8

   Locate hidden leaks (optional)
   If pressure is dropping but no external leak is visible, depressurize, add UV dye per the dye manufacturer's dosing, re-pressurize, then drive the vehicle on a short cycle (if safe) and re-inspect with a UV light. Pay attention to seepage at hose-to-fitting junctions.
9. 9

   Depressurize and remove the tester
   Use the tester's bleed valve to slowly release pressure to zero before disconnecting. Remove the adapter from the expansion tank by hand. Wipe the neck and surrounding area dry.
   ⚠Never disconnect a pressurized adapter — it will eject coolant and can damage the tank neck.

Reassembly

1. Verify coolant level is still between MIN and MAX. Top up only with Tesla-spec battery/motor coolant (G-48 equivalent) if needed. DO NOT substitute conventional coolant.
2. Reinstall the expansion tank cap (original or replacement) and tighten to the cap's hand-tight detent — do not overtighten.
3. Wipe down the engine bay / frunk tray to remove any spilled coolant; coolant residue makes future leak diagnosis difficult.
4. Reconnect the low-voltage (12V/16V) battery: positive terminal first, then negative. Torque to OEM specification — refer to Tesla Service Manual.
5. Close the frunk and any cowl panels disturbed during access.

Verification

• Power the vehicle on. Check the touchscreen for any coolant-related alerts (e.g. 'Coolant level low', 'Vehicle systems power reduced'). No new alerts should appear.
• With the vehicle awake, listen for the coolant pumps cycling — they should run smoothly with no air-gurgle sounds. Persistent gurgling indicates air in the system, which is normal after a top-up and should self-bleed within a few drive cycles.
• Drive the vehicle for 10–15 minutes to bring the cooling system to operating temperature, then park and let it cool for 2+ hours. Re-check coolant level — it should remain at the same mark.
• Inspect the previously suspect area one more time with the system warm (but not opened) for any new weeping.
• Note: Tesla recommends a coolant system inspection at 4 years / 50,000 miles. Log this pressure test against that interval. If the test failed and a leak was found in a non-HV component (radiator, hose, expansion tank), repair can proceed; if the leak is at the HV battery, drive units, Octovalve, superbottle, or heat pump, refer the vehicle to a Tesla-certified technician.

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